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X-ORIGINAL-URL:https://aero.iisc.ac.in
X-WR-CALDESC:Events for Department of Aerospace Engineering
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TZID:Asia/Kolkata
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TZOFFSETFROM:+0530
TZOFFSETTO:+0530
TZNAME:IST
DTSTART:20250101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260814T110000
DTEND;TZID=Asia/Kolkata:20260814T133000
DTSTAMP:20260907T224720
CREATED:20260811T114531Z
LAST-MODIFIED:20260824T064859Z
UID:10000146-1786705200-1786714200@aero.iisc.ac.in
SUMMARY:MTech(res)  Parallel Particle Tracking for Turbulent Round Jets
DESCRIPTION:Particle tracking in turbulent jets is essential for an accurate Lagrangian understanding of jet flows. While parallel algorithms and numerical schemes to compute flow fields can be scaled to a large number of computing processes\, the same is not necessarily true for particle tracking. This thesis presents an analysis of the parallel efficiency of particle tracking in the specific context of round turbulent jets.\nA particle tracking module was developed and integrated with Xcompact3d – a well-established flow solver with strong and weak scaling up to 100\,000 processes. The module uses trilinear velocity interpolation scheme and a first-order Euler integration scheme with sub-stepping for particle advancement. Velocity data is exchanged via a halo API provided by 2DECOMP&FFT – the domain decomposition library that Xcompact3d builds upon. Particle data is exchanged via MPI collectives. Additional exchange algorithms that aim to avoid the scalability limitations of MPI collectives are available to the user. However\, the choice of algorithms for data exchange is often constrained by flow and simulation parameters. \nThe module is validated using an analytical velocity field and subsequently employed for DNS and LES of turbulent jets with particles. Particle concentration profiles are used to assess accuracy. The results demonstrate the capability of the integrated code to accurately track particles over multiple simulation runs. The particle numbers used for these simulations are comparable or higher than the number of grid points as opposed to most studies in the literature where particle numbers are much lower than the number of grid points. \nA detailed wall-time and particle-load analysis is done to assess the parallel efficiency and identify performance limitations. Particle tracking and exchange are the largest contributors to simulation time after flow field computation. The wall-time for particle tracking increases with the number of particles in the domain. A large difference is observed between the average wall-time and maximum wall-time across computing processes which is attributed to particle load imbalance. In contrast\, the particle exchange wall-time across computing processes is similar because of the MPI collectives being used for particle data exchange. However\, the number of particles\, and consequently\, the size of data being exchanged\, is a small fraction of the number of particles being tracked. A particle load-analysis reveals considerable variation in the number of particles being tracked by individual processes\, with the maximum difference in particle count amongst processes being as high as three orders of magnitude. \nThe results obtained highlight the challenges in implementing particle tracking at scale. While strategies to mitigate the impact of non-scalable collectives for particle exchange exist\, algorithms to mitigate the severe particle-load imbalance in the context of turbulent jets have not been adequately studied and are urgently required\, which is identified as the key area for future work. \n  \nSpeaker : Nikhil Jayswal \nResearch Supervisor: Prof. Joseph Mathew
URL:https://aero.iisc.ac.in/event/mtechres-parallel-particle-tracking-for-turbulent-round-jets/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/Nikhil-Jayswal.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260810T110000
DTEND;TZID=Asia/Kolkata:20260810T130000
DTSTAMP:20260907T224720
CREATED:20260808T055603Z
LAST-MODIFIED:20260811T060138Z
UID:10000145-1786359600-1786366800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg):Tonal acoustic radiation from turbulent subsonic jets
DESCRIPTION:Acoustic tones in the near field of a Mach 0.9\, Reynolds number 10^6 round jet are investigated using large-eddy simulations (LES) performed with the explicit filtering LES (EFLES) approach. The jet is issued into the ambient through a cylindrical nozzle. Pressure spectra at observer locations in the upstream direction reveal the presence of tones which are 15–20 dB more intense than the background turbulent mixing noise. Spectral Proper Orthogonal Decomposition (SPOD) of the pressure field in the near-nozzle region reveals two distinct categories of tones. The first category comprises tones whose frequency corresponds to high order radial and azimuthal ductmodes of the nozzle. Their spatial amplitude distribution revealed by SPOD at these frequencies show significant support within the nozzle as expected for the natural hard-wall duct modes. These duct modes are scattered at the nozzle lip and radiate in the upstream direction and explain the tonal radiation observed in the LES at their corresponding frequencies. This mechanism has been extensively studied using Wiener-Hopf models applied to a cylindrical vortex sheet (Munt\, 1977; Rienstra\, 2003; Samanta and Freund\, 2008). The second category of tones observed have frequencies that are not hard wall duct mode frequencises. Their spatial amplitude distribution revelaed by SPOD for these frequencies is characterized by significant support within the jet potential core. Empirical dispersion relations constructed from the LES suggest that these tones arise from resonance in the potential core due to coupling between the upstream-propagating guided jet mode (GJM) and the upstream- and downstream-propagating duct-like modes (Schmidt et al.\, 2017; Towne et al.\, 2017) near the upper cut-off frequency of the guided jet mode (Bogey\, 2021). However\, the mechanism by which tones radiate from the potential core has not yet been established. This motivates the theoretical investigation in this thesis that focuses on the dynamics of the guided jet mode and its interaction with the nozzle lip leading to tonal upstream acoustic radiation. The interaction between the GJM and the nozzle lip is analyzed using a Wiener–Hopf formulation with the jet modelled as a semi-infinite cylindrical vortex sheet and the nozzle with a vanishingly-thin sharp edge. When the GJMs are cut-on\, these solutions show that an incident GJM is reflected as a downstream-traveling soft-duct mode\, a scattered Kelvin–Helmholtz (K–H) mode and a transmitted upstream-traveling hard-wall duct mode. The reflective efficiency of GJM increases with frequency and is greatest near their upper cut-off frequency. This explains why tones associated with potential core resonance occur near the upper cut-off frequency of the GJM. In addition\, the GJM is scattered as acoustic waves to the far field\, primarily in the upstream direction. The scattered wavefronts are most intense along the outer nozzle wall. The scattered waves propagate to the far field where they generate distinctive directivity patterns that show excellent agreement with the LES-computed far-field directivity reported by Bogey (2021). These results provide a mechanistic explanation for how tones generated by potential core resonance radiate to the far field through scattering of the guided jet mode at the nozzle lip. Acoustic tones in the near field of a Mach 0.9\, Reynolds number 10^6 round jet are investigated using large-eddy simulations (LES) performed with the explicit filtering LES (EFLES) approach. The jet is issued into the ambient through a cylindrical nozzle. Pressure spectra at observer locations in the upstream direction reveal the presence of tones which are 15–20 dB more intense than the background turbulent mixing noise. Spectral Proper Orthogonal Decomposition (SPOD) of the pressure field in the near-nozzle region reveals two distinct categories of tones. The first category comprises tones whose frequency corresponds to high order radial and azimuthal ductmodes of the nozzle. Their spatial amplitude distribution revealed by SPOD at these frequencies show significant support within the nozzle as expected for the natural hard-wall duct modes. These duct modes are scattered at the nozzle lip and radiate in the upstream direction and explain the tonal radiation observed in the LES at their corresponding frequencies. This mechanism has been extensively studied using Wiener-Hopf models applied to a cylindrical vortex sheet (Munt\, 1977; Rienstra\, 2003; Samanta and Freund\, 2008). The second category of tones observed have frequencies that are not hard wall duct mode frequencises. Their spatial amplitude distribution revealed by SPOD for these frequencies is characterized by significant support within the jet potential core. Empirical dispersion relations constructed from the LES suggest that these tones arise from resonance in the potential core due to coupling between the upstream-propagating guided jet mode (GJM) and the upstream- and downstream-propagating duct-like modes (Schmidt et al.\, 2017; Towne et al.\, 2017) near the upper cut-off frequency of the guided jet mode (Bogey\, 2021). However\, the mechanism by which tones radiate from the potential core has not yet been established. This motivates the theoretical investigation in this thesis that focuses on the dynamics of the guided jet mode and its interaction with the nozzle lip leading to tonal upstream acoustic radiation. The interaction between the GJM and the nozzle lip is analyzed using a Wiener–Hopf formulation with the jet modelled as a semi-infinite cylindrical vortex sheet and the nozzle with a vanishingly-thin sharp edge. When the GJMs are cut-on\, these solutions show that an incident GJM is reflected as a downstream-traveling soft-duct mode\, a scattered Kelvin–Helmholtz (K–H) mode and a transmitted upstream-traveling hard-wall duct mode. The reflective efficiency of GJM increases with frequency and is greatest near their upper cut-off frequency. This explains why tones associated with potential core resonance occur near the upper cut-off frequency of the GJM. In addition\, the GJM is scattered as acoustic waves to the far field\, primarily in the upstream direction. The scattered wavefronts are most intense along the outer nozzle wall. The scattered waves propagate to the far field where they generate distinctive directivity patterns that show excellent agreement with the LES-computed far-field directivity reported by Bogey (2021). These results provide a mechanistic explanation for how tones generated by potential core resonance radiate to the far field through scattering of the guided jet mode at the nozzle lip. Comparison of the Wiener–Hopf predictions with the LES-computed pressure spectra in the present investigation reveals excellent agreement at lower frequencies but deviations at higher frequencies. At lower frequencies\, the SPOD modes are qualitatively similar to the corresponding Wiener–Hopf solutions. In contrast\, at higher frequencies\, the scattered waves originating from the nozzle lip undergo secondary scattering at the slanted section of the outer nozzle wall\, causing them to lift away from the wall. The findings suggest two possible strategies for mitigating the tones generated by the potential core resonance: (i) modifying the nozzle-lip geometry and (ii) modifying the outer nozzle-wall geometry. \n  \nSpeaker: NAGA SARAS CHANDAN VEMPATI \nResearch Supervisor: Santosh Hemchandra
URL:https://aero.iisc.ac.in/event/ph-d-enggtonal-acoustic-radiation-from-turbulent-subsonic-jets/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/NAGA.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260807T110000
DTEND;TZID=Asia/Kolkata:20260807T130000
DTSTAMP:20260907T224720
CREATED:20260804T053733Z
LAST-MODIFIED:20260811T060311Z
UID:10000144-1786100400-1786107600@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Aerodynamics and Stability of a Generic Tailless UAV in Ground Effect
DESCRIPTION:Tailless UAVs are stealthy\, high-subsonic configurations used for deep penetration into contested airspace. These configurations have wing with moderate leading edge sweep angle with no definite fuselage and lack both horizontal tail and vertical tail which makes the aerodynamics of these configurations very unique. The increase in autonomous UAVs in recent times have led to renewed interest in this class of configurations. Autonomous take-off and landing of tailless UAVs are complex technologies that require a detailed understanding of the underlying aerodynamic flow physics. The current literature on the ground effects focusses mainly on conventional configuration or high swept delta wings.  This work focusses on understanding the aerodynamic behavior of a typical tailless UAV near the ground and its influence on the stability characteristics. RANS CFD analysis is carried out at different ground heights\, angle of attack and side slip angle. Studies are also carried to understand the effect of roll orientation effect on the ground effects. The  effect of ground on the elevon behavior near the ground are also brought out. Unsteady CFD Analysis are conducted for different sink rates and pitch angles and compared with Static Ground Effects.\n The lift coefficient under Steady Ground Effects was observed to decrease near the ground at lower angle of attack and increase at high angle of attack. The region between the ground and aircraft acts like a venturi at low angle of attack. At high angle of attack\, ramming effect is observed due to increase in the pressure on the bottom surface. The drag coefficient does not change at lower angle of attack whereas significant reduction is observed at higher angle of attack due to the reduction in the induced drag.  The UAV shows a reduction in directional stability near the ground. The rolling moment due to side slip angle shows a stable behavior near the ground.  The roll orientation of the UAVs impacts the rolling moment behavior near the ground providing increased rolling moment near the ground which has a tendency to counter the direction of the roll.  Unsteady CFD Analysis is conducted for different sink rates and pitch angles and compared with Static Ground Effects which shows significant change especially at lower pitch angles. \n The aerodynamic changes introduced by the  presence of ground impacts the Stability of the UAV significantly.  The Stability  changes are particularly important for the tailless UAV as it is neutrally stable in the longitudinal and directional plane. A increase in Static Margin of 0.5% is observed at the lowest ground  height  (h/b = 0.15). There is also marginal increase in weather cock stability (Cnβ)  and roll stability (Clβ) at high angle of attack near the ground. The dynamics of the tailless UAV near the ground has interesting behavior near the ground. The short period mode has stabilizing behavior near the ground whereas the Dutch roll tends to be slightly unstable near the ground. The roll orientation of the UAV seems to impact the Dutch roll mode changing from slightly unstable to a slightly stable behavior.  The aerodynamics and stability aspects are highly coupled for tailless UAV. The understanding of tailless UAV near the ground will be key for development of control schemes for robust take-off and landing of these Configurations. \n  \nSpeaker :  B Saravanan \nResearch Supervisor :  N Balakrishnan \n 
URL:https://aero.iisc.ac.in/event/aerodynamics-and-stability-of-a-generic-tailless-uav-in-ground-effect/
LOCATION:AE Conference Room \, AE 003
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/Saravanan.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260806T113000
DTEND;TZID=Asia/Kolkata:20260806T130000
DTSTAMP:20260907T224720
CREATED:20260717T092701Z
LAST-MODIFIED:20260802T105215Z
UID:10000137-1786015800-1786021200@aero.iisc.ac.in
SUMMARY:Ph .D.(Engg.): Explicit Filtering LES of turbulent swirling flows and multi-regime hydrogen flames
DESCRIPTION:The need to decarbonize power generation and aviation has established hydrogen as a promising fuel for next generation gas turbine combustion systems. However\, its high chemical reactivity significantly increases the propensity for autoignition and flashback under lean premixed conditions commonly used in hydrocarbon combustion systems. New combustor concepts based on direct fuel injection address these problems but typically produce lifted flames. These types of flames exhibit multi-regime combustion\, in which premixed and non-premixed combustion regions co-exist within highly turbulent swirling flow fields. Accurate numerical prediction of such reacting flows remains a major challenge as traditional models developed for hydrocarbon flames often fail to reliably predict the stabilization and combustion characteristics of multi-regime hydrogen flames. This thesis proposes a regime-sensitive combustion model using the thickened flame approach to extend the explicit filtering large eddy simulation (EFLES) method for computations of high Reynolds number (Re) reacting flows. A combustion regime index (CI) is defined based on the alignment between the gradients of mixture fraction and oxygen mass fraction to distinguish between premixed and non-premixed regions. The flame thickening treatment is applied selectively in premixed regions only. The model is implemented within an in-house high-order finite-difference flow solver that employs structured multi-block overlapping meshes to represent complicated geometries encountered in practical combustion systems. The predictive capability of the overall numerical methodology is systematically assessed through a series of increasingly complex flow configurations relevant to swirl-stabilized hydrogen combustors. The first case corresponds to an isothermal (Re ~ 27000) flow in the PRECCINSTA single nozzle swirl combustor. EFLES solutions show excellent agreement with the experimental data for flow field statistics and shape of the vortex breakdown bubble. Spectral proper orthogonal decomposition applied on time resolved velocity fields confirms that the EFLES method accurately reproduces the broadband turbulence structures and the coherent\, narrow band\, self-excited precessing vortex core oscillation. The combustion model performance is then evaluated using a canonical lifted slot jet flame configuration\, comprising a nitrogen diluted hydrogen slot jet of Re=8000 at 400 K issuing into a co-flow of heated air at 850 K. Entrainment of air into the jet core results in a stratified rich premixed flame alongside the primary non-premixed flame branch. The LES predicted flame lift-off height and flow field statistics are in good agreement with companion direct numerical simulation (DNS) results. Differences between LES and DNS solutions are small in premixed flame regions but increase with mesh spacing in non-premixed flame regions. The CI field is shown to clearly distinguish the two flame branches. This result is further validated a-posteriori using chemically explosive mode analysis (CEMA). Combined with EFLES\, the combustion model accurately predicts mixture fraction conditioned thermochemical statistics\, combustion mode distributions and the downstream evolution of premixed and diffusion flame branches in the lifted slot jet hydrogen flame. Finally\, a turbulent lifted hydrogen flame in the dual-swirl HYLON burner is investigated as a practical test case. The time-averaged mean flame shape and liftoff height is well captured in the LES solution. Good agreement is obtained between LES predictions and experimental measurements for statistics of velocity\, temperature\, and major-species mole fractions. CEMA reveals that a partially premixed flame branch is formed along the inner shear layer due to entrainment of hydrogen into the high-velocity annular air stream. The central diffusion flame branch is located within the vortex breakdown bubble between the fuel jet and the recirculating lean combustion products. The distribution of key thermochemical variables in mixture fraction space is also analyzed to characterize the two flame branches. Overall\, the results demonstrate that the proposed multi-regime thickened flame model\, coupled with explicit filtering LES provides a robust framework for high-fidelity LES of turbulent hydrogen flames. The methodology reproduces turbulent flow features\, flame stabilization and mixed combustion regimes across canonical and practical configurations. These results make the case for evaluating the performance of EFLES at higher operating pressures towards realizing a reliable computational engineering method for the design and analysis of future hydrogen gas turbine combustors. \nSpeaker :  ANINDYA DATTA \nResearch supervisor : Santosh Hemchandra
URL:https://aero.iisc.ac.in/event/ph-dengg-colloquium/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/ANINDYA.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260805T110000
DTEND;TZID=Asia/Kolkata:20260805T130000
DTSTAMP:20260907T224720
CREATED:20260728T061746Z
LAST-MODIFIED:20260802T102832Z
UID:10000141-1785927600-1785934800@aero.iisc.ac.in
SUMMARY:MTech(Res) : Design of an Ex-Situ Gas Sampling Layout with Various Probes and Their Performance Assessment for Accurate Emission Measurements
DESCRIPTION:Chemical kinetic mechanism development and validation require quantitative species data from canonical flames. Burner-stabilized pre -mixed flames provide a stationary post-flame region directly comparable to one-dimensional kinetic simulations. Ex-situ gas sampling delivers absolute CO and NO mole fractions from this region. The extraction step introduces two coupled biases. Reactions can continue inside the probe\, and the probe can perturb the flame upstream of the inlet. This thesis develops a coordinated ex-situ sampling framework for atmospheric McKenna burner-stabilized CH₄/air flames. The framework combines a sampling and dilution layout\, five sampling probes\, and a staged correction methodology. The measurements span fuel-lean to fuel-rich flames at three heights above the burner. The sampling and dilution layout is one of the principal contributions of the present work. The complete layout was designed and assembled in this work to adapt a portable gas analyzer (PG-350) for laboratory flame diagnostics. The PG-350 is built for stationary-source emissions monitoring rather than laboratory flame research. The design repurposes this industrial emissions instrument for high-precision species measurement in flames. The adapted instrument serves fundamental academic flame research. The layout delivers a conditioned\, metered\, and range-compatible sample to the analyzer. A vacuum pump extracts the sample using a sampling probe and drives it through the line. Two water-cooled drain separators\, designed and fabricated in this work\, remove the post-flame moisture. An Alicat mass flow meter measures the conditioned sample flow rate. A controlled N₂ dilution arrangement extends the CO measurement range beyond the analyzer’s full scale for the rich flames. Five sampling probes represent four reaction-quenching strategies. The aerodynamic-quench (AQ) probe was designed using a one-dimensional gas-dynamics model developed in this work. A brute-force screening selected its geometry against the pump and analyser constraints. The water-cooled (WC)\, pressure-quench (PQ)\, and uncooled probes were sized using non-reacting two-dimensional axisymmetric CFD. The uncooled-metal (UC-M) probe serves as a hot-wall reference. The uncooled-quartz (UC-Q) probe isolates the wall-material effect under the same geometry. Each probe was assessed experimentally and through two-dimensional probe-resolved reacting CFD in ANSYS Fluent. A residence-time method quantified the probe-induced upstream shift of the sampling location for the designed probes. A staged correction methodology recovers the sampled-gas composition from the conditioned analyzer reading. It corrects the mass flow meter reading for its gas-property mismatch. It then removes the imposed dilution and restores the moisture removed during conditioning. An independent route back-calculates the dilution ratio from paired CO₂ measurements. The methodology propagates the input uncertainties through the correction chain using the GUM framework. Reported values quote the expanded uncertainty on the corrected species. The corrected CO and NO were evaluated against a one-dimensional chemical kinetic simulation of the unperturbed flame. The comparison accounts for the probe-induced upstream shift of the sampling location. Each designed probe draws its sample from a location displaced toward the burner relative to its tip. The three designed probes were compared against the reference at their displaced sampling locations. The pressure-quench probe is the most consistent for both species. The water-cooled probe is a close alternative. The vacuum pump performance degraded due to moisture condensation in the pump head. Therefore\, it held the AQ suction above its design value throughout the campaign. The AQ probe is therefore off-design and cannot be ranked on equal terms. The uncooled-metal probe shows a large NO deficit in the rich flames from hot-wall surface reactions. The uncooled-quartz probe isolates the metal wall as the origin of this deficit. These rankings measure consistency with the kinetic reference rather than absolute accuracy. This work delivers outcomes of broader use to the combustion community. The framework offers documented guidelines to the community for ex-situ sampling experiments. It provides a comprehensive assessment of how each quenching strategy performs and which probe suits a given measurement. The corrected CO and NO data are suitable for chemical kinetic mechanism development and validation. Many detailed chemistry mechanisms exist\, yet reacting CFD of practical combustion devices requires reduced mechanisms that reproduce the target species profiles. The present setup allows reduced mechanisms to be validated quickly across flames spanning fuel-lean to fuel-rich conditions. A validated reduced mechanism can then support detailed CFD analysis of practical combustion systems. \n  \nSpeaker :  SARVAGYA SHARMA \nResearch Supervisor :  Irfan Ahmed Mulla
URL:https://aero.iisc.ac.in/event/mtechres-design-of-an-ex-situ-gas-sampling-layout-with-various-probes-and-their-performance-assessment-for-accurate-emission-measurements/
LOCATION:STC Conference Hall\, Ground Floor\, Department of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/SARVAGYA.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260727T113000
DTEND;TZID=Asia/Kolkata:20260727T130000
DTSTAMP:20260907T224720
CREATED:20260723T053755Z
LAST-MODIFIED:20260802T095511Z
UID:10000138-1785151800-1785157200@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Wave Propagation in Small Scale Structure Modelled With Nonlocal Continuum Theory
DESCRIPTION:This thesis develops analytical and computational frameworks for studying static and dynamic behaviour in nonlocal elastic structures\, focusing on wave propagation\, stress localization\, and guided-wave phenomena at micro- and nano-scales\, where size-dependent effects fall outside classical continuum mechanics. Eringen’s differential nonlocal elasticity theory and higher-order continuum formulations are used to capture these small-scale interactions.\nThe work first examines plane-stress problems with geometric singularities (cracks\, circular and elliptical holes) using a finite element formulation based on a second-order stress-gradient nonlocal model. While the static displacement equation stays independent of the nonlocal length-scale parameter\, nonlocal effects become significant near large displacement gradients and stress concentrations. Unlike classical elasticity\, which predicts singular stresses at crack tips\, the nonlocal formulation produces bounded stress fields. Dynamically\, nonlocal interactions primarily affect inertia terms\, altering transient response rather than stiffness.\nTo handle high-frequency wave propagation efficiently\, a spectral super-element method combines wavenumber-frequency domain spectral elements with conventional finite elements\, enabling accurate modelling of cracks and holes while retaining exact wave representation in uniform regions. This eliminates classical stress singularities and supports applications such as MEMS analysis. A related hybrid spectral-finite element framework further restricts finite element use to defect regions\, cutting computational cost while accurately predicting stress concentration and intensity factors\, validated against commercial FE software for plates with holes and cracks.\nThe second major focus is guided-wave behaviour in elastic waveguides and plates under nonlocal constitutive laws. Analytical Lamb-wave dispersion relations are derived via Helmholtz decomposition with traction-free boundary conditions. Using Eringen’s second-order nonlocal model and strain-gradient theory\, the study reveals non-classical effects\, including wavenumber saturation\, modified cut-off frequencies\, and escape frequencies\, in symmetric and antisymmetric Lamb modes. Comparisons show that simpler one-dimensional models (Mindlin-Herrmann rod\, Timoshenko beam) can reproduce key guided-wave characteristics of the full two-dimensional nonlocal model.\nFinally\, a coupling framework uses local models away from defects and nonlocal elasticity near cracks. Since such coupling typically causes spurious reflections at domain interfaces\, a novel transition-zone strategy is proposed to suppress these artifacts. Implemented in a frequency-domain spectral element framework\, it is applied to waveguides with horizontal and vertical through-width cracks\, achieving accurate\, efficient\, and physically consistent wave analysis.\nOverall\, this thesis establishes a unified framework for nonlocal wave propagation and stress analysis in structures with discontinuities\, offering practical tools for wave-based sensing\, structural health monitoring\, ultrasonic nondestructive evaluation\, and micro- and nano-scale structural design. \n  \nSpeaker :  Ajeet Kumar Yadav \nResearch Supervisor : Prof S. Gopalakrishnan
URL:https://aero.iisc.ac.in/event/ph-d-engg-wave-propagation-in-small-scale-structure-modelled-with-nonlocal-continuum-theory/
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/Ajeet.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260724T113000
DTEND;TZID=Asia/Kolkata:20260724T130000
DTSTAMP:20260907T224720
CREATED:20260723T070319Z
LAST-MODIFIED:20260802T100840Z
UID:10000139-1784892600-1784898000@aero.iisc.ac.in
SUMMARY:Modelling the response of Turbulent CH4-Air premixed flame using Resolvent Analysis
DESCRIPTION:An understanding of the flame transfer function (FTF) is essential for predicting the onset of combustion instabilities in gas turbine combustors\, where flow oscillations excited by acoustic forcing drive burning area and heat-release oscillations that can couple unfavourably with combustor acoustic modes. The heatrelease response is expensive to characterize directly through time resolved simulation\, motivating reduced order approaches that operate on a single time-averaged mean flow. In the present work\, we develop and critically assess a resolvent analysis (RA) based reduced order model for the FTF of a turbulent premixed methane air round jet flame (φ=0.8\, T_u=800 K\, Re≈1500)\, with the time-averaged base flow obtained from explicit-filtering large eddy simulation (EFLES) of the unforced flame. Two aspects of the RA formulation are examined systematically: the passive versus active treatment of the flame i.e.\, whether coherent reaction rate fluctuations are dropped or retained in the linearised species/energy equations and the choice of heatrelease rate closure across four models of increasing physical detail (a global Arrhenius model\, ARR-A; a Bayesian calibrated modified Arrhenius model with a cold-boundary correction\, ARR-B; and global and local Eddy Break-Up models\, EBUG and EBUL). RA-predicted FTF gain and phase are validated against harmonically forced LES over St=[0.2\,1.2]\, and the spatial structure of the leading RA response modes is compared against SPOD modes extracted from the same forced LES. FTF phase is recovered robustly by all four models up to St≈0.8\, since the leading velocity response mode and hence the convective phase speed governing flame surface wrinkling is set almost entirely by the mean vorticity and density field and shows weak dependence on the heatrelease closure. FTF gain is far more model dependent: the passive ARR-B model gives the best overall quantitative match to LES\, with excellent agreement at St=0.2 where non-linear flame tip pocket shedding is negligible\, while both EBU models underpredict gain across the full St range because their reaction rate is a function of progress variable and density alone\, giving identically zero sensitivity to temperature and fuel mass fraction fluctuations. The resolvent gain spectrum collapses toward strongly low rank behaviour with increasing St a single mode pair recovers 99% of the response for St≥0.6\, while three mode pairs are needed at St=0.2 and the Arrhenius-type models produce systematically higher gains than the EBU models owing to their spatially extended sensitivity field. Switching from the passive to the active formulation leaves the velocity response essentially unchanged but qualitatively alters the thermochemical response: temperature and species fluctuations\, which propagate downstream as undamped travelling waves in the passive case\, decay beyond the flame brush in the active case\, in closer qualitative agreement with the LES SPOD modes. This improved qualitative fidelity does not\, however\, translate into better FTF gain prediction the active formulation degrades gain agreement for every model examined\, a result traced to the single free parameter in each heatrelease closure being calibrated only against the mean heatrelease field\, with no constraint on the local dynamic sensitivities that the active formulation feeds back into the linear operator. The overall picture that emerges is that RA provides a reliable and computationally efficient framework for predicting FTF in axisymmetric premixed-flame configurations. The results further establish a clear pathway toward improved quantitative gain prediction through reaction-rate closures that represent the local dynamic sensitivities of the flame more faithfully\, enabling increasingly predictive low-order models from time-averaged base flows. Further work is needed to improve the active flame approach by developing reaction rate closures that capture both the mean heatrelease field and the local dynamic sensitivities governing flame response feedback. \n  \nSpeaker : SATYAM CHAUHAN \nResearch Supervisor :  Santosh Hemchandra
URL:https://aero.iisc.ac.in/event/modelling-the-response-of-turbulent-ch4-air-premixed-flame-using-resolvent-analysis/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/08/SATYAM.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260624T150000
DTEND;TZID=Asia/Kolkata:20260624T170000
DTSTAMP:20260907T224720
CREATED:20260623T083955Z
LAST-MODIFIED:20260712T055011Z
UID:10000133-1782313200-1782320400@aero.iisc.ac.in
SUMMARY:MTech(Res): Characterization of Turbulent Spots near the onset of Transition in a Flat-plate Boundary Layer
DESCRIPTION:Boundary layer (BL) transition to turbulence occurs through the inception\, growth\, and merging of turbulent spots. Understanding these spots is vital for predicting aerodynamic performance in disturbance-dominated environments like gas turbines.\n\nHowever\, conventional spot identification has been limited by subjective\, manual thresholding. The first phase of this work introduces a novel\, threshold-free demarcation scheme combining a Pre-Multiplied Wavelet Energy (PMWE) detector—scaled with BL thickness and log-transformed to establish an objective criterion for detection— along with a Gaussian Mixture Model (GMM) as a classifier. The framework generates wall-normal and spanwise variations of intermittency to a good accuracy and is validated across Direct Numerical Simulation (DNS) and wind-tunnel datasets for multiple transition scenarios.\n\n​Using this detection framework\, we track the precursors of spots (velocity spikes) upstream. Analysis of the instantaneous energetics of the pre-transitional region reveals that while stable streaks exhibit positive production within their cores and weak dissipation along their interfaces\, localized streak breakdown is consistently preceded by a distinct patch of negative turbulence production (a counter-gradient energy transfer back to the mean flow) co-located with intense dissipation. Crucially\, velocity spikes lacking this negative production signature fail to convert into downstream turbulent spots. Thus the presence of negative production appears to be a necessary precursor to spot inception.\n\n​Furthermore\, we evaluate the statistics near the transition front using a new intermittency-based conditioning method. While conventional conditional averaging at fixed streamwise locations obscures the physics by blending spots at different developmental stages\, conditioning along surfaces of constant local intermittency aligns spots at equivalent evolutionary stages much better. This approach reveals that as the transition onset is approached from downstream\, local turbulence production and dissipation increase manyfold. The sharp rise in these quantities signifies an abrupt\, highly localized energy transfer during the inception of spots\, occurring even while the corresponding skin friction coefficient remains close to laminar values.\n\nSpeaker : Yash Naiwar\n\nResearch Supervisor : Sourabh Suhas Diwan
URL:https://aero.iisc.ac.in/event/mtechres-characterization-of-turbulent-spots-near-the-onset-of-transition-in-a-flat-plate-boundary-layer/
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/07/Yash.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260610T103000
DTEND;TZID=Asia/Kolkata:20260610T120000
DTSTAMP:20260907T224720
CREATED:20260609T045550Z
LAST-MODIFIED:20260615T100351Z
UID:10000130-1781087400-1781092800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Distributed Artificial Intelligence Technology for Robotic Swarms: An Interpretable Online Learning Perspective
DESCRIPTION:Robotic swarms offer immense potential for critical operations such as search and rescue\, surveillance\, and environmental monitoring\, owing to their distributed nature and redundancy. However\, the operational reliability of swarms heavily depends on a continuous\, closed-loop process: extracting high-fidelity or accurate collective situational awareness from distributed observation\, and subsequently utilizing that awareness for cooperative decision control in non-stationary environments. To achieve reliable operation across unstructured and dynamic domains\, the robotic swarm must maintain resilience when subjected to adverse situations. For instance\, in real-world target searching and surrounding\, environmental hazards can cause physical sensors to degrade or fail\, leading to significant prediction biases\, communication link drops\, or a complete loss of ground truth. Further\, robots operating in such dynamically evolving situations are frequently tasked with conflicting spatial objectives\, such as aggressively pursuing an agile target while safely navigating dense clutter\, requiring intelligent control to manage limited actuation and actuator velocity saturation limits. To address these demands\, this thesis develops an online learning based Distributed Artificial Intelligence Technology (DAITy) for robotic swarms\, which establishes a collective Situational Awareness – Decision Control (SA-DC) loop capable of executing resilient swarm cooperation and coordination across unstructured and non-stationary environments. \nThis thesis first focuses on extracting high-fidelity collective situational awareness from distributed observation under severe sensory biases and intermittent communication failures\, enabling the robots to accurately determine own-location and predict target behavior. The Distributed Learning-based Decentralized Cooperative Localization (DL-DCL) and Distributed Online learning-based Multi-Estimate (DOME) fusion frameworks are proposed. These supervised loss-driven online learning frameworks dynamically learn an information fusion strategy to combine pose estimates (or target position predictions) from onboard sensors (or prediction algorithms) and neighboring robots. To handle dynamically evolving situations and recover target trajectories despite severe environmental interference\, both frameworks incorporate periodic reset mechanisms to shed historical inertia alongside bounded loss functions to prevent explosive estimation errors from faulty sensors. Theoretically\, both frameworks establish the convergence of the fusion weights to the optimal local or social estimate/prediction; while DL-DCL’s theoretical analysis involves deterministic communication network\, DOME’s analysis involves random network. Quantitative evaluations demonstrate that DL-DCL improves own-pose estimation performance by approximately 40% under severe sensor faults\, while DOME achieves up to a 74% reduction in target position prediction loss compared to baselines that include both covariance-based and online learning methods. \nWhile supervised online learning is effective when landmarks or leaders are available\, swarms often operate in unstructured\, GPS-denied environments entirely lacking such ground-truth supervisors. To tackle this challenge\, the second contribution of this thesis introduces a reward-driven online learning framework based on concepts of independent learning or self-learning. The Autonomous Online Learning (AOL) framework enables resilient cooperative target monitoring by a reward-driven weighted information fusion process extracting accurate target location from limited\, intermittent exteroception among the robots in the swarm. Three variants are developed\, introducing a novel perturbation-greedy reward design that facilitates exploration-exploitation in the fusion weight space. The AOL framework empowers the swarm to isolate faulty robots and prioritize reliable information dynamically in adverse situations. Through rigorous convergence analysis\, the framework theoretically guarantees that the fusion weights converge to prioritize the most accurate information source. The top-performing variant\, AOL-1P\, demonstrates a 182.2% to 652% improvement in target detection scores and a 94.7% to 150.4% improvement in tracking closeness across varying swarm sizes over established baselines\, ensuring robust monitoring even when 50% of the total swarm population is undergoing permanent sensor failures. \nWith a high-fidelity situational awareness established\, the swarm must execute distributed decision control in non-stationary environments. Standard online optimization methods are often ineffective or inefficient on physical robotic swarms due to the dual challenge of simultaneous multi-objective balancing and actuator descent-step saturation\, particularly when target maneuvers force the swarm into dense clutter requiring seamless transitions between target tracking\, pursuit\, and collision avoidance. As the third contribution\, this thesis proposes the Softmax-Adaptive Objective Balancing in Multi-Objective Online Gradient Descent (SAO-MOOGD) framework. SAO-MOOGD utilizes a bounded loss signal to update objective weights using a softmax function\, enabling dynamic weighted averaging of the objective gradients. This enables simultaneous\, real-time balancing of competing goals\, such as decoupled collision avoidance versus target tracking. Theoretical analysis reveals dynamic regret bounds that explicitly quantify the error induced by physical velocity saturation\, showing that sub-linear regret growth can be guaranteed when proportional velocity controllers are appropriately tuned. Further\, theoretical analysis proves the exponential decay of the aggregation gap regret under non-degenerate loss margins. Complementing these theoretical guarantees\, the approach leverages the 1/2-Lipschitz continuity of the softmax operator to ensure smooth physical trajectory blending\, effectively eliminating heuristic limit-cycling. Across extensive ROS-Gazebo evaluations using TurtleBot3s\, SAO-MOOGD achieves improved multi-objective performance. Compared to high-tracking heuristic baselines\, it exhibits up to 5.5% lower target tracking accuracy while reducing collisions by up to 67% and lowering control effort by 30%. Further\, it demonstrates improved resilience\, incurring a reduction of less than 1% in tracking accuracy even under 40% communication packet drops and severe Gaussian sensory noise. \nDuring real-world deployments\, maintaining precise geometric configurations under physical disturbances is crucial for the Situational Awareness – Decision Control Loop. As the final contribution\, this thesis introduces the Topological Online Learning for Displacement-based (TOLD) formation control framework. Unlike conventional robust controllers that regulate node-level inputs without modifying the interaction topology\, TOLD performs real-time edge-level adaptation to preserve the swarm’s structural integrity in dynamically evolving situations. Two strategies are proposed: Online Gradient Flow (OGF) with unconstrained weights\, and Online Exponential Gradient Flow (OExpGF) with non-negative convex weights. Theoretical analysis proves that under directed communication topologies\, the convex OExpGF strategy drives single-integrator agents to asymptotic consensus\, whereas the unconstrained OGF approach guarantees a bounded structural distortion. Evaluated in both simulation and physical hardware experiments using Crazyflie 2.0 quadrotors\, TOLD significantly reduces formation distortion. OGF achieves a 62% reduction and OExpGF over a 31.4% reduction in median formation distortion compared to static interaction topologies in hardware experiments. \nOverall\, this thesis develops Distributed Artificial Intelligence Technology (DAITy) for robotic swarms from an interpretable online learning perspective\, seamlessly connecting collective information to decentralized situational awareness and decision control. Extensive evaluations across theoretical domains\, high-fidelity simulations\, and real-world hardware testbeds confirm the effectiveness and practical applicability of the proposed frameworks in unstructured and dynamically evolving situations. \nSpeaker: Shubhankar Gupta \nResearch Supervisor: Prof. Suresh Sundaram \n  \nTeams Meeting Link: Join: https://teams.microsoft.com/meet/48118742709693?p=5x8mXnmrvKS0j3tx9g\nMeeting ID: 481 187 427 096 93\nPasscode: 9JQ6Tg2d
URL:https://aero.iisc.ac.in/event/ph-d-engg-distributed-artificial-intelligence-technology-for-robotic-swarms-an-interpretable-online-learning-perspective/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/06/Shubhankar.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260416T110000
DTEND;TZID=Asia/Kolkata:20260416T130000
DTSTAMP:20260907T224720
CREATED:20260413T094427Z
LAST-MODIFIED:20260413T094427Z
UID:10000119-1776337200-1776344400@aero.iisc.ac.in
SUMMARY:M.Tech(Res) : Effect of hydrogen-enrichment on soot formation in laminar gaseous hydrocarbon flames
DESCRIPTION:Gaseous and particulate pollutants pose a significant threat to human health and the environment\, prompting regulatory action to address major sources of emissions. Soot is a key particulate pollutant. Recently\, emission standards for commercial aeroengines have been revised\, necessitating the mitigation of soot emissions. Investigating the soot formation process is a key step towards reducing emissions. Soot formation is a complex process that poses a challenge to the chemical kinetics community. Predicting soot is computationally expensive and challenging\, requiring reliable reduced mechanisms for practical fuels. The primary obstacle is the lack of systematic data to develop and validate chemical kinetics models for soot prediction. Hydrogen (H2) is being explored as a means to decarbonize the automotive\, aviation\, and power generation sectors. However\, implementing pure H2 in practical devices is difficult due to higher operating temperatures and flame speeds. Alternatively\, H2 can be blended into traditional hydrocarbon fuels. The addition of H2 influences the combustion chemistry of hydrocarbon fuels\, which consequently leads to changes in the composition of combustion products. The aviation industry uses practical fuels to form turbulent flames. However\, the complexity of practical fuels and flow fields makes it difficult to predict the concentrations of combustion emissions. A systematic study of soot formation in laminar gaseous-fuel flames can aid in developing reduced soot reaction mechanisms and understanding the soot formation process. This work reports a database of soot concentrations for C1–C4 hydrocarbons (methane\, ethane\, propane\, and butane) under laminar premixed and non-premixed conditions. Additionally\, the influence of H2 blending on soot formation is examined for these fuels. The parameters\, such as soot volume fraction (fv)\, distributions of soot precursors (PAH) and OH\, and gas temperature\, are measured using laser-based diagnostic techniques. The study of soot formation was performed on two different burner configurations: premixed and non-premixed. The premixed burner stabilized flames with φ = 2.3 were stabilized on the McKenna burner equipped with a stagnation plate. To ensure flame stability\, a mixture of O2 and Ar was used as the oxidizer. The reactant flow rates for test cases are selected such that the carbon influx (Cin)\, C/O ratio\, and O2 fraction in oxidizer are kept constant. The non-premixed flames were stabilized on a coflow burner. The flow conditions were selected to maintain a constant Cin\, thereby isolating the influence of Cin on soot. For both flame configurations\, H2 is added up to 40 % (by volume) to a base hydrocarbon fuel. H2 addition has three primary effects: thermal\, dilution\, and chemical. The chemical effect of H2 on soot is isolated using a reference flame\, created by replacing H2 with helium. The comparison of fv with this reference flame allows for the quantification of the chemical effect of H2 on soot. The fv is measured for both premixed and non-premixed flames by using the laser-induced incandescence (LII) technique. The distribution of PAH is measured using the planar laser-induced fluorescence (PLIF) technique. Additionally\, for non-premixed flames\, the distributions of OH and the temperature field were measured using the PLIF technique. The elemental carbon-to-hydrogen ratio (C/H) governs the maturity of soot. The soot maturity changes with height above the burner (HAB)\, introducing a bias in LII measurements. The LII fluence curve trends with HAB in premixed flames are used to estimate the relative change in soot maturity. These trends along HAB are used to estimate relative changes in the optical properties of soot particles (E(m)). PAH are the precursors to soot formation. However\, interpreting PAH-LIF (IPAH) trends is challenging due to the dependence of LIF on temperature and quenching by combustion products. In this work\, an empirical approach is used to correct the IPAH in premixed flames for these dependencies. Additionally\, the extinction signature in radial IPAH profiles is used to obtain absorption-based PAH concentration. This approach mitigates the bias in interpreting the PAH trends in premixed flames. Soot volume fraction (fv) increases monotonically with carbon number (C1 to C4) for alkanes in both laminar premixed and non-premixed flames. The total soot loading parameter is used to examine the overall sooting tendency. The soot loading decreases relative to neat flames with H2-enrichment for all fuels. The extent of suppression of soot formation by H2 addition is greater in premixed flames than in non-premixed flames. Cin is examined relative to CxHy/He flames. It was observed that Cin is strongly dependent on the type of fuel. H2 enrichment inhibits pyrolysis in ethylene (alkene) fuel\, contributing to delayed soot onset relative to the helium reference flame. Conversely\, H2 promotes (relative to helium) pyrolysis in non-premixed C1–C4 alkane flames\, thereby enhancing soot. In premixed alkane flames\, H2 suppresses soot in the inception-dominated region but enhances soot in growth-dominated regions. This contrasts with ethylene flame\, where H2 reduces soot formation throughout HAB. These findings reveal the fuel-specific impact of H2 enrichment on soot formation\, providing a systematic dataset to support the validation of chemical kinetics models and the design of low-emission combustion systems. The performance of the state-of-the-art soot reaction mechanism to predict fv is assessed against measurements. Additionally\, chemical kinetics analysis is performed to examine the chemical effect of H2 on soot formation. \n  \nSpeaker : Choudhari Aditya Sunil  \nResearch Supervisor :  Irfan Ahmed Mulla
URL:https://aero.iisc.ac.in/event/m-techres-effect-of-hydrogen-enrichment-on-soot-formation-in-laminar-gaseous-hydrocarbon-flames/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/04/CHOUDHARI.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260217T110000
DTEND;TZID=Asia/Kolkata:20260217T130000
DTSTAMP:20260907T224720
CREATED:20260213T055505Z
LAST-MODIFIED:20260213T055505Z
UID:10000115-1771326000-1771333200@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) :Experimental Investigation of Autoignition Pathways and Shock-Train Dynamics During Mode Transition in a Dual-Mode Supersonic Cavity Combustor
DESCRIPTION:Hypersonic propulsion systems capable of sustained atmospheric flight are critical enablers for future reusable launch vehicles\, long-range high-speed transport\, and responsive global strike platforms. Among the various air-breathing concepts\, scramjet engines offer unmatched efficiency at hypersonic speeds by utilizing atmospheric oxygen and avoiding the mass penalties associated with onboard oxidizers. However\, the practical realization of scramjet propulsion is fundamentally constrained by two interrelated challenges: reliable ignition and flame stabilization under extremely short residence times\, and robust operation across a wide flight envelope that necessitates smooth transition between supersonic (scramjet) and subsonic (ramjet) combustion modes. Dual-mode scramjets (DMSJ) are designed to address this requirement\, but their operability is limited by complex\, strongly coupled interactions between shock structures\, boundary-layer separation\, fuel-air mixing\, chemical kinetics\, and unsteady pressure fields during mode transition. A central difficulty in hypersonic combustors is that global flow conditions typically yield Damköhler numbers well below unity\, rendering conventional flame-holding ineffective. Localized enhancement of thermochemical coupling through elevated temperature\, pressure\, and residence time is therefore essential to initiate and sustain combustion. Cavity-based flameholders have emerged as a promising solution due to their passive\, low-drag configuration and ability to generate recirculation zones that promote autoignition and flame anchoring. Nevertheless\, cavity-stabilized combustors introduce additional challenges: strong sensitivity to geometry\, concentration of thermal loads\, susceptibility to unsteady shear-layer oscillations\, and complex coupling with shock-train dynamics during scram-to-ram transition. Despite extensive cold-flow investigations of isolator shock trains\, their behaviour under reacting\, high-enthalpy conditions where heat release actively modifies the flow remains insufficiently characterized. This doctoral research discusses a systematic experimental investigation of autoignition pathways\, flame stabilization mechanisms\, and shock-train dynamics in a cavity-stabilized dual-mode supersonic combustor. Experiments are conducted in a direct-connect high-enthalpy facility at the Advanced Propulsion Research Laboratory (APRL)\, Indian Institute of Science. The combustor operates at flight relevant conditions of total temperature of 1500 ± 30 K and static pressure of 43 kPa\, which corresponds to Mach 5.5 flight conditions at 28 km altitude. The experimental test article features an optically accessible supersonic combustor with a single/twin cavity configuration and is designed for an inlet Mach 2.5. Time-resolved Schlieren imaging\, CH* and C2* chemiluminescence\, and high-frequency wall-pressure measurements are employed to resolve unsteady flow-flame interactions governing ignition and mode transition. Two cavity geometries with identical depth but different length-to-height ratios (L/H = 5 and 8.5) were examined to quantify the influence of geometry on ignition robustness and shock–flame coupling. For the L/H = 5 configuration\, ethylene ignition occurred downstream in the diverging duct at a global equivalence ratio of ϕg ≈ 0.3\, followed by upstream flame propagation and eventual stabilization along the shear layer. In contrast\, the L/H = 8.5 cavity enabled earlier and more robust ignition upstream\, triggered by shock-assisted autoignition behind an X-type shock formed through interaction between the cavity reattachment shock and a top-wall separation bubble. The larger cavity generated stronger pressure deficits\, deeper shear-layer penetration\, and self-sustained oscillations at approximately 527 Hz\, highlighting the critical role of cavity geometry in enhancing local Damköhler numbers. Optical diagnostics technique of two-wavelength chemiluminescence (CH* and C2*) revealed ignition kernels forming preferentially in high-temperature lean regions before stabilizing near stoichiometric zones. Shock-induced compression was shown to significantly reduce ignition delay\, enabling autoignition even for fuels with substantially longer chemical timescales. Fuel-blending experiments established a limiting ignition-delay threshold\, providing quantitative guidance for fuel selection in practical hypersonic combustors. The scram-to-ram mode transition occurred at ϕg ≈ 0.58 for both geometries and was marked by the formation of a pre-combustion shock train\, initiated due to combustion induced boundary layer separation. The L/H = 8.5 cavity sustained stable ram-mode operation\, whereas the L/H = 5 configuration frequently reverted to early scram-mode behavior\, indicating weaker shock-flame coupling and reduced buffering capacity against back-pressure fluctuations. Scaling analysis of shock-train dynamics yielded Strouhal numbers (St) an order of magnitude lower than the reported values in the literature based on isothermal shock-train oscillation studies. This demonstrated the dominant influence of heat release and shock-train coupling. Proper orthogonal decomposition (POD) analysis further revealed tight coupling between shock-train motion and upstream flame propagation\, identifying critical regions in the combustor with substantial heat release fluctuations. Finally\, symmetric dual-cavity configurations were explored to assess coupled shear-layer dynamics. While dual cavities enhance residence time\, their interaction introduces additional unsteady modes\, underscoring the need for geom etry-aware stabilization strategies. Overall\, this work directly addresses critical propulsion challenges for hypersonic vehicles by elucidating the mechanisms governing ignition reliability\, shock-assisted autoignition\, and mode-transition stability in cavity-based dual-mode scramjets. The findings provide mechanistic understanding and scalable design guidelines essential for the development of robust\, operable hypersonic air-breathing propulsion systems. \n  \nSpeaker :  Sumit Lonkar \nResearch Supervisor: Pratikash Prakash Panda
URL:https://aero.iisc.ac.in/event/ph-d-engg-experimental-investigation-of-autoignition-pathways-and-shock-train-dynamics-during-mode-transition-in-a-dual-mode-supersonic-cavity-combustor/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/02/SUMIT.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260209T111500
DTEND;TZID=Asia/Kolkata:20260209T130000
DTSTAMP:20260907T224720
CREATED:20260202T091939Z
LAST-MODIFIED:20260204T061202Z
UID:10000113-1770635700-1770642000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Multi-Agent Coordination using Convex Formations and Binary Tree Structures
DESCRIPTION:Multi-agent systems are increasingly deployed in missions involving large-scale tasks with complex objectives that are beyond the capability of a single agent. Such missions demand computationally efficient coordination strategies that ensure safety\, reliable operation\, and ease of implementation\, particularly in dynamic and uncertain environments. This thesis investigates coordination strategies in multi-agent systems\, specifically addressing the problems of distribution of agents on an enclosing boundary\, cooperative target capture and containment\, and traversal through constrained spaces.\n\nThe first part of the thesis presents a convex layer-based strategy that assigns collision-free paths to a swarm of point-sized agents to reach an enclosing circular boundary. Leveraging the construction of convex layers from the initial positions of agents\, a novel search space for an agent on a convex layer is defined as an angular region enclosed between the lines passing through the agent’s position and normal to its supporting edges. A goal assignment policy is proposed\, which designates a unique goal position on the boundary within the search space of an agent. Subsequently\, the proposed framework is extended to polygonal boundaries\, considering disc-shaped agents. Therein\, the proposed policy assigns a goal position to each agent in order of decreasing overlap between their search spaces and the polygonal boundary\, while excluding angular regions corresponding to already assigned goal positions. Further\, a layer-wise speed assignment rule is proposed\, which ensures collision-free trajectories for the agents. Simulation studies assess the proposed method under various real-world considerations\, including the finite size of the agents\, a six-degree-of-freedom quadrotor model\, uncertainties in initial position information\, and communication delays.\n\nIn the second part\, the problem of multiple pursuers engaging a single evader is considered in two complementary scenarios. Firstly\, the problem of capturing the evader in an unbounded region is addressed. As the key construct\, the evader’s proximity region is characterized by the region generated by the Voronoi diagram constructed using the positions of the pursuers and the evader. Pursuers’ velocity inputs are deduced as a function of the position and velocity of the vertices of the evader’s proximity region and the evader. A motion policy is proposed that directs the vertices of the evader’s proximity region toward its centroid\, under which the region is analytically shown to shrink exponentially over time\, irrespective of the evader’s motion policy. In addition\, using the Chebyshev radius of the proximity region\, an upper bound on the time of evader capture is derived. Simulation studies demonstrate the effectiveness of the proposed method under various evader maneuvers and in scenarios where evader position information is noisy. In a scenario complementary to evader capture\, a containment problem is considered\, wherein multiple pursuers are desired to encapsulate a moving evader. Considering the engagement between the evader and the centroid of the convex hull of pursuers\, a variable deviated pursuit guidance law is proposed\, which achieves a tail-chase rendezvous between the evader and the centroid. Subsequently\, a cooperative control strategy is presented\, which drives the convex hull of pursuers to confine the evader through a prescribed edge while preserving the formation rigidity. Simulation results demonstrate the efficacy of the proposed method under various evader maneuvers.\n\nThe final part of the thesis addresses the problem of sequential traversal of multiple UAVs through a narrow gap. A hierarchical binary tree is constructed with its nodes defined by the UAVs’ initial positions and the gap entry point\, presenting a routing framework that provides an ordered sequence of waypoints to each UAV. A cost function is formulated that accounts for the UAV path lengths and the angles between branches at the tree nodes\, and a binary tree is constructed by minimizing that cost using a genetic algorithm coupled with a greedy strategy. In conjunction\, a decentralized scheduling policy is proposed\, in which each UAV is assigned conflict-free time slots at nodes that are identified with potential collisions. Simulation scenarios illustrate the effectiveness of the proposed method\, and Monte Carlo studies assess its scalability.\n\nOverall\, the thesis presents deterministic and computationally efficient multi-agent coordination strategies by leveraging ideas from convex geometry and binary trees. Experimental flight trials on a nano-quadrotor platform are also conducted\, further demonstrating the practicality of the proposed coordination methods.\n\nSpeaker : Gautam Kumar \n\nResearch Supervisor : Ashwini Ratnoo
URL:https://aero.iisc.ac.in/event/ph-d-engg-multi-agent-coordination-using-convex-formations-and-binary-tree-structures/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/02/Gautam.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260119T150000
DTEND;TZID=Asia/Kolkata:20260119T170000
DTSTAMP:20260907T224720
CREATED:20260116T043058Z
LAST-MODIFIED:20260119T103611Z
UID:10000112-1768834800-1768842000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) :  Turbulence Energy Cascade in Physical  Space in a Turbulent Channel Flow
DESCRIPTION:A comprehensive investigation of the energy and enstrophy cascade in physical space in a turbulent channel flow is presented for four Reynolds numbers. Bandpass filtering techniques are employed to isolate scales and quantify inter-scale interactions through kinetic energy flux\, enstrophy generation\, and enstrophy flux. Two bandpass filter formulations used in the literature are quantitatively assessed by comparing the output.\nThe mean energy and enstrophy cascades are shown to be predominantly local for all the Reynolds numbers. Away from the wall\, the degree of locality decreases while a broader range of scales participate in the cascade. Interestingly the distance at which the inter-scale flux peaks shows a distance-from-wall scaling\, implying relevance of the attached-eddy formalism to energy cascade in scale space (in addition to its relation ​ to momentum transport in physical space). Vorticity stretching as the underlying mechanism of cascade is studied through vorticity alignment statistics. The vortices show preferential alignment with intermediate eigenvector for smaller scale ratios and closer to the wall\, while alignment with the most extensional eigenvector is observed at larger scale ratios and away from the wall. The preferential alignment shows a complex dependence on the wall-normal distance\, suggesting that the wall has important influence on both energy transfer rates and the geometry of structures. Notwithstanding this\, the contribution from most extensional eigenvector dominates enstrophy generation for all conditions. The scaling of energy flux with scale size\, scale ratio\, wall-normal distance\, and Reynolds number is obtained using dimensional arguments and is validated against numerical results.  As the cascade progresses\, the energy at small scales gets concentrated in a small region of space\, reflected as intermittency in enstrophy and energy fluxes. The skewness and kurtosis increase at smaller length scales but they show weak increase with the Reynolds number. The morphology of energy flux and enstrophy iso-surfaces are characterized through Minkowski functionals. Enstrophy structures at small scales are like flattened long tubes\, while large-scale structures are blob-like or short-tube-like. The large-scale structures generally exhibit lower values of filamentarity. Energy flux structures show a similar behaviour\, with near-wall structures being more flattened compared to those farther from the wall. These findings remain unaffected by an increase in threshold for getting the iso-surfaces.\nOverall\, the present study provides new insights into the locality\, scaling\, and morphology of the energy and enstrophy cascade in the channel flow\, offering a unified framework for interpreting multi-scale turbulence dynamics in wall-bounded flows.\n\nSpeaker :  Aditya Anand\n\nResearch Supervisor :  Sourabh Suhas Diwan
URL:https://aero.iisc.ac.in/event/ph-d-engg-turbulence-energy-cascade-in-physical-space-in-a-turbulent-channel-flow/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/01/Aditya123.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260116T160000
DTEND;TZID=Asia/Kolkata:20260116T170000
DTSTAMP:20260907T224720
CREATED:20260113T100659Z
LAST-MODIFIED:20260113T100659Z
UID:10000111-1768579200-1768582800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Development of an ultra-miniature wall-shear-stress sensor
DESCRIPTION:Shear stress at the wall is a quantity of fundamental importance in wall-bounded flows. It determines skin-friction drag and the dynamics of flow separation. From an engineering standpoint\, it is a key parameter which dictates the overall aerodynamic performance and structural loading of flight vehicles. Hence\, there is a natural motivation for the development of new techniques and sensors that can offer well-resolved measurements of wall shear stress. Conventionally\, the techniques of hot-film anemometry and oil-film interferometry are used for wall-shear-stress measurements. These techniques\, however\, are severely limited in the spatio-temporal resolution that they can offer. Advances in micro and nano-fabrication techniques over the past three decades have led to the advent of MEMS-based floating element sensors. While MEMS sensors offer better resolution than conventional methods\, the inertia of the floating element limits their temporal response. Miniaturizing the sensing element of the thermal anemometry probe is a viable solution to obtain high-resolution measurements. This approach has been successfully demonstrated with velocity measurements in turbulent flows with ultra-miniature hot-wire probes\, which are able to fully resolve the turbulence spectrum even at high Reynolds numbers.\n\nMotivated by the success of ultra-miniature hot-wire probes in velocity measurements\, the present effort is directed at the development\, fabrication\, and demonstration of an ultra-miniature sensor\, based on the principles of thermal anemometry\, for wall-shear-stress measurements. The sensor design essentially consists of platinum filaments deposited on a thermally oxidized silicon substrate with electrical contact pads. The fabrication is carried out by oxide growth on a clean silicon wafer\, followed by two-layer electron beam lithography\, metal deposition\, and lift-off processes. Titanium is used for adhesion in the first layer\, followed by platinum deposition for the sensing element in the second layer. Dry reactive ion etching is used\, when needed\, to suspend the sensing element. Basic voltage-current characterization of the sensor is carried out prior to packaging of the sensors for use.\n\nA demonstration of the sensor is made in a turbulent boundary layer flow. The packaged sensor is integrated onto a flat plate in a low-speed wind tunnel facility\, and wall-shear-stress measurements are made in the turbulent boundary layer flow over the flat plate in the momentum thickness Reynolds number range of 1500 to 2500. The sensor is calibrated in the boundary layer flow in an in-situ manner by estimating the mean wall-shear-stress through hot-wire measurements of the flow velocity profile at different freestream velocities. The sensor fully resolves the spectrum of turbulent fluctuations in wall shear stress. The probability density distributions of wall-shear-stress fluctuations are found to match well with data reported in the literature\, thereby validating the sensor’s performance. Overall\, this work demonstrates the viability of making high-fidelity wall-shear-stress measurements using ultra-miniature thermal anemometry sensors. It lays the foundation for the development of a practical sensing tool for application outside the laboratory\, in a real-world environment.\n\nSpeaker : Keshanjali Gaur\n\nResearch Supervisor : Prof. Duvvuri Subrahmanyam
URL:https://aero.iisc.ac.in/event/ph-d-engg-development-of-an-ultra-miniature-wall-shear-stress-sensor/
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/01/Keshanja.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260105T110000
DTEND;TZID=Asia/Kolkata:20260105T130000
DTSTAMP:20260907T224720
CREATED:20260102T043026Z
LAST-MODIFIED:20260105T113025Z
UID:10000108-1767610800-1767618000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) :Studies on the Mixing Layer Between Supersonic Supersonic Co-flows
DESCRIPTION:Two supersonic streams merging together in a co-flow configuration are encountered in several engineering systems\, such as high-speed propulsion devices and supersonic ejectors. The thin mixing layer that develops between the two streams is dominated by compressibility effects and is prone to shock interactions in shock-dominated flows. The convective Mach number is defined relative to dominant large-scale structures in the mixing layer and is typically used to characterise the mixing layer. A key observation from previous studies on canonical supersonic-supersonic mixing layers having zero streamwise pressure gradient (ZPG-ML)\, which has a significant bearing on system design\, is that the growth of the mixing layer is significantly reduced as the convective Mach number increases. In applications\, however\, streamwise pressure gradients can exist due to the flow topology\, but there are very few studies on the effects of the streamwise pressure gradient on the growth of mixing layers (SPG-ML)\, especially in shock-dominated flows\, which motivates this study. Further\, there is a need to enhance mixing rates for compact design\, which can be carried out using passive geometric modifications\, and the effects of techniques such as discrete injection through holes and vortex generators like lobes on SPG-ML are not well studied. We study the mixing layer between supersonic-supersonic coflows in a specially designed supersonic mixing layer experimental facility\, and using high-fidelity Large Eddy Simulations carried out using the OpenFOAM framework. The Mach number combinations of the two streams (2.0\, 3.0) and (2.5\, 3.0)\, with a typical convective Mach number of 0.23\, are investigated. The flow is experimentally examined using high-speed schlieren and wall static pressure measurements. First\, the LES framework is validated on existing experimental/DNS computations on ZPG-ML\, and the computations are found to simulate the mixing layer characteristics well. The flow topology of the SPG-ML involves the generation of an oblique shock and an expansion fan at the point of confluence\, as well as the development of the mixing layer downstream in the presence of a streamwise pressure gradient. The shock further reflects from the wall and impinges on the mixing layer. The wall static pressure profiles obtained from the LES simulations agree well with the experimental wall static pressure measurements. The mixing layer growth rate of the SPG-ML before shock interaction is 15% higher than ZPG-ML. Shock interaction significantly increases the three-dimensionality of the turbulent structures in the mixing layer\, particularly in the p resence of high baroclinic torques\, and enhances the growth rate. In the current study\, the mixing layer is found to curve after the shock interaction\, thereby sustaining an increase in the mixing layer growth rate compared to previous studies. Two different techniques of introducing streamwise vortices into the mixing layer are investigated\, the first where discrete holes connect the high-pressure side to the low-pressure side\, leading to a jet into the supersonic stream\, generating counter-rotating vortices. In the second technique\, elliptic lobes generate large streamwise vortices. Both techniques are found to increase the mixing layer growth rate before the interaction. Shock interaction is found to break up vortices and promote three-dimensionality in the milder case of the jet through the holes. In the case of lobes\, the streamwise vortices are strong enough to retain their connectedness despite getting significantly modified by the shock interaction. These observations have implications for the application of such techniques to enhance mixing in shock-dominated flows. Detailed comparative investigations of different supersonic-supersonic mixing layer configurations are examined using experiments and LES data \n  \nSpeaker:  PANCHABUDHE LAKHAN MADANJI  \nResearch Supervisor: Srisha Rao M V
URL:https://aero.iisc.ac.in/event/ph-d-engg-studies-on-the-mixing-layer-between-supersonic-supersonic-co-flows/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/01/PANCHABUDHE-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20251230T103000
DTEND;TZID=Asia/Kolkata:20251230T130000
DTSTAMP:20260907T224720
CREATED:20251229T130027Z
LAST-MODIFIED:20251231T083130Z
UID:10000107-1767090600-1767099600@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Enhancing Precise Label Prediction and Imbalance Robustness in Multi-Label Learning
DESCRIPTION:Multi-label learning (MLL) addresses learning problems in which a single data instance may simultaneously belong to multiple semantic categories. This formulation arises naturally in many real-world applications\, including image and video understanding\, medical diagnosis\, text categorization\, and bioinformatics. In many of these settings\, it is not sufficient to merely rank relevant labels higher than irrelevant ones; instead\, models must accurately identify the exact set of labels associated with each instance. Such exact label prediction is critical when each label carries direct semantic or operational meaning\, for example when detecting disease conditions in medical data or identifying pedestrians and traffic signs in autonomous driving scenes. In addition\, real-world deployments frequently expose multi-label models to out-of-distribution (OOD) inputs caused by domain shifts\, novel concepts\, or evolving environments\, making reliable OOD detection an important requirement. Many practical applications are also sequential in nature\, where data and label spaces evolve over time\, leading to the continual multi-label learning (CMLL) problem in which models must acquire new knowledge while mitigating catastrophic forgetting. Together\, these considerations motivate the need to study multi-label learning with emphasis on exact label prediction\, robustness to data imbalance\, improved OOD detection\, and learning under continual data arrival. \nThe first contribution of this thesis introduces Bipolar Networks\, a novel architectural formulation for multi-label classification designed to improve exact label prediction. Unlike conventional single-output architectures that produce continuous confidence scores per label\, Bipolar Networks represent each label using two complementary outputs that encode positive and negative evidence. The final label decision is derived from the relative difference between these outputs\, enabling exact label predictions. To support effective training of this architecture\, the thesis develops a family of bipolar loss functions by reformulating standard objectives such as Binary Cross-Entropy and Focal Loss\, along with margin-based variants. Extensive experiments on benchmark datasets demonstrate that Bipolar Networks consistently improve F1 scores while maintaining competitive mean average precisions. \nBuilding on the improved discriminative behaviour of Bipolar Networks\, the second contribution addresses out-of-distribution detection in multi-label learning. While most existing OOD detection methods are designed for single-label classification or rely on computationally intensive mechanisms\, this thesis proposes a bipolar joint energy score tailored to the bipolar architecture. By leveraging the improved exact label prediction capability of Bipolar Networks\, the proposed scoring function enables more effective separation between in-distribution and out-of-distribution samples in multi-label settings\, demonstrating that stronger multi-label classification performance on in-distribution data can naturally translate into improved OOD detection. \nThe third contribution presents Learn What Matters\, a generalizable training framework that enhances exact label prediction without modifying model architectures or loss formulations. Learn What Matters operates at the optimization level by selectively masking parameter updates based on the ratio of gradient to parameter magnitudes\, suppressing low-information updates while rescaling the remaining gradients to preserve learning dynamics. This approach acts as a form of dropout during backpropagation and directs learning toward informative regions of the parameter space. Applied to standard single-output multi-label networks trained with ranking-based losses\, Learn What Matters yields substantial improvements in F1 score with only marginal impact on mAP scores\, providing a model-agnostic alternative to architectural modifications. \nThe fourth contribution explores biologically inspired learning approaches for multi-label classification. Drawing inspiration from neural computation in the human brain\, the thesis develops several bio-inspired models\, including Bipolar Spiking Neural Networks\, Adaptive Margin Spiking Neural Networks\, and NIMBLE\, a neuro-inspired multi-label learning framework. These methods leverage spike-based computation\, selective update mechanisms\, and adaptive stability–plasticity behavior to naturally support exact label prediction and efficient learning. Experimental results demonstrate that these biologically motivated designs improve exact label prediction and imbalance robustness in multi-label settings. \nFinally\, the thesis extends the proposed architectures and learning algorithms to the continual multi-label learning setting\, where data arrives sequentially without access to past samples or task identities. The resulting methods are task-agnostic and memory-free\, and empirical evaluations across multiple benchmarks show consistent improvements in exact label prediction and reduced catastrophic forgetting. Overall\, this thesis presents a unified framework spanning architectural design\, optimization strategies\, and biologically inspired learning for advancing exact label prediction\, OOD detection\, and continual learning in multi-label learning models. \n  \nSpeaker :  Sourav Mishra \n  \nResearch Supervisor: Prof. Suresh Sundaram
URL:https://aero.iisc.ac.in/event/ph-d-engg-enhancing-precise-label-prediction-and-imbalance-robustness-in-multi-label-learning/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/12/Sourav.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20251222T150000
DTEND;TZID=Asia/Kolkata:20251222T170000
DTSTAMP:20260907T224720
CREATED:20251218T100932Z
LAST-MODIFIED:20251218T100932Z
UID:10000104-1766415600-1766422800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Characterization of time-frequency behavior of flow intermittency in transitional boundary layers
DESCRIPTION:The importance of transitional flow studies can be realized from the fact that it acts as a bridge between the laminar and turbulent flows. The present work deals with the investigation of time-frequency characteristics of transitional flows and their modelling\, which is presented in three parts.\nFirst\, we propose a wavelet-transform based smooth detector function which is used to detect the presence of turbulent spots in a signal. We also propose a novel wavelet transform based algorithm to calculate the intermittency for various transitional and turbulent boundary layers with the primary objective to remove the subjectivity of current methods. The method is also used to calculate the intermittencies for temporal and spatial distributions of velocities of a computational dataset. The algorithm involves calculation of a sensitive detector and then obtaining an indicator based on Monte-Carlo like iterations. A cut-off on the number of iterations ​is obtained based on RMS of the laminar part of the signal. The method is also able detect the turbulent/non-turbulent interface in wall-normal and wall-parallel planes. This wide spectrum of results prove the generality of the scheme\, which to our knowledge has been demonstrated for the first time.\nSecondly\, the substructures of stream-wise velocity fluctuations within a turbulent spot are investigated using time-spectral and probability density function(PDF) based analyses. The pre-multiplied Fourier spectrum shows that the turbulent spots appear rather  “suddenly” at the onset of transition. The high frequency structures inside a near-wall turbulent spot at the onset of transition are found to be highly time localized. The presence of large amplitude events near the onset location hints towards a near “singular” structure within a nascent spot that has high frequencies\, amplitudes and time localization. It is also seen that the transition process only modifies the structures at higher frequencies and the lower frequencies remain almost unchanged. For lower frequencies\, the structure throughout the transition zone\, for all the transition as well as the turbulent boundary layer cases show a universal nature.\nIn the third part\, Cellular Automaton (CA) is used to model the growth\, propagation and merging of turbulent spots. CA simulations are shown to handle a variety of different practical/theoretical spot generation scenarios. These simulations are computationally inexpensive and easily parallelizable. They represent a promising avenue for modelling the kinematics of turbulent spots.\n\nSpeaker : Satyajit De\n\nResearch Supervisor : Sourabh S. Diwan
URL:https://aero.iisc.ac.in/event/ph-d-engg-characterization-of-time-frequency-behavior-of-flow-intermittency-in-transitional-boundary-layers/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/12/Satyajit.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20251219T110000
DTEND;TZID=Asia/Kolkata:20251219T130000
DTSTAMP:20260907T224720
CREATED:20251212T053059Z
LAST-MODIFIED:20251218T103035Z
UID:10000101-1766142000-1766149200@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Investigations on Elastic Deformation of Ferromagnetic Rods and Ribbons
DESCRIPTION:Bulk ferromagnetic materials exhibit Joule magnetostriction with characteristic strain magnitudes on the order of (10^{-6}) to (10^{-4})\, which is often insufficient for the displacement requirements of modern soft robotic and adaptive structural systems. Ferromagnetic elastic slender structures provide a promising alternative\, offering the potential for large actuation displacements under small external magnetic fields. This enhanced response results from a rich coupling between magnetic and elastic phenomena in slender structures\, where external magnetic fields can induce significant displacements with relatively small field strengths. This thesis develops a novel unified theoretical framework to describe the coupled magnetoelastic behavior of ferromagnetic elastic rods and ribbons. The framework formulates the total energy functional\, incorporating elastic and magnetic energy components for both soft and hard ferromagnetic materials. The elastic energy is derived from Kirchhoff and Wunderlich models for rods and ribbons. The magnetic energy is formulated using the micromagnetic energy functional composed of exchange\, anisotropy\, magnetostriction\, demagnetization\, and Zeeman energies. Central to the framework is the interplay between elastic energy and the competing magnetic effects: demagnetization energy in soft ferromagnets and Zeeman energy in hard ferromagnets. \nIn the first part of this thesis\, we construct the total energy formulation for ferromagnetic rods undergoing planar deformation and utilize Kirchhoff kinetic analogy for our investigation. A detailed bifurcation analysis distinguishes the Hamiltonian phase portraits of elastic rods and soft ferromagnetic rods in longitudinal and transverse magnetic fields\, revealing distinct subcritical and supercritical pitchfork bifurcations. The extension of Kirchhoff’s kinetic analogy to ferromagnetic rods enables the prediction of equilibrium shapes under various boundary conditions and applied fields. However\, the kinetic analogy framework does not directly address the stability of these equilibrium states. \n\n                                                                                                                                            Motivated by this limitation\, the second part presents a comprehensive one-dimensional model for ferromagnetic elastic rods/ribbons systematically incorporating micromagnetic energy for curved geometries. The resulting equilibrium equations are derived for both soft and hard magnetic cases\, which are then solved numerically to trace load–deflection responses. Stability analysis via a Sturm–Liouville eigenvalue approach reveals tensile critical buckling loads for soft ribbons and uncovers novel stable post-buckling configurations\, especially for fixed-fixed boundary conditions under transverse magnetic fields. For hard ferromagnetic ribbons\, the buckling loads are shifted\, but the corresponding equilibrium shapes approach those of purely elastic ribbons. The restriction to planar deformations\, however\, leaves open the question of whether these configurations remain stable with respect to fully three-dimensional perturbations.\nTo address this issue\, the third part extends the study to spatially deforming ferromagnetic elastic rods subjected to combined magnetic and terminal mechanical loading. The Hamiltonian derived from the total energy is analyzed\, revealing a significant difference: the purely elastic and hard ferromagnetic rods exhibit subcritical pitchfork bifurcations\, whereas the soft ferromagnetic rod shows no bifurcation under similar conditions. Furthermore\, localized buckling deformation of soft ferromagnetic rod shows non-collinear straight segments.\nThis work is\, to the best of our knowledge\, the first to demonstrate the role of demagnetization energy in the large deformation of ferromagnetic slender structures. As one of the dominant contributions to the micromagnetic energy functional\, the demagnetization energy is inherently geometry dependent and therefore crucial to structural deformation. As the slender structure deforms and its geometry changes and the demagnetization energy is correspondingly modified. Our results provide an understanding of the interplay of magnetic and elastic forces\, paving the way for the design of advanced smart materials and potential applications in magnetically-actuated soft robots\, adaptive medical devices\, and remote actuation.\n\nSpeaker:  Mr. G R Krishna Chand Avatar\n\nResearch Supervisor : Dr. Vivekanand Dabade
URL:https://aero.iisc.ac.in/event/ph-d-engg-investigations-on-elastic-deformation-of-ferromagnetic-rods-and-ribbons/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20251201T110000
DTEND;TZID=Asia/Kolkata:20251201T130000
DTSTAMP:20260907T224720
CREATED:20251201T040004Z
LAST-MODIFIED:20251201T040004Z
UID:10000097-1764586800-1764594000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg) : Autorotation of Single-Winged Spinning Samaras
DESCRIPTION:Nature has consistently served as a powerful source of innovation\, offering elegant and sustainable solutions to complex engineering problems. Among these\, the spinning samara seed stands out as a biologically efficient system for passive aerial transport. Samaras\, such as those from mahogany and Buddha coconut trees\, exhibit stable autorotative descent\, making them strong candidates for biomimicry in aerial delivery systems. Understanding and replicating the flight mechanics of samaras requires accurate analytical modelling. The dynamics of a single-winged spinning samara can be described using Newton’s laws and Euler’s rigid‐body equations\, while the aerodynamic forces acting on the wing can be derived from the Navier–Stokes equations or using Blade Element Momentum Theory (BEMT). Together\, these frameworks provide a foundation for predicting its motion\, thrust generation\, and stability in samara-inspired designs. Building on this theoretical basis\, the present thesis delivers a comprehensive experimental study on the bioinspired engineering of single-winged spinning samaras\, focusing on their aerodynamic behavior\, kinematic characteristics\, structural morphology\, and wake dynamics. To investigate the kinematics\, a custom-designed drop rig was developed to capture high-resolution visual data of the steady-state descent. Parameters such as descent velocity\, coning angle\, wingtip trajectory\, and precession were extracted and analyzed. The results revealed a complex motion involving coupled coning and precession\, challenging simplified theoretical models that typically assume a steady\, non-precessing descent. Parallel morphological studies using high-resolution 3D scanning of natural samaras highlighted spanwise variations in chord length\, camber\, and sweep\, which contribute significantly to aerodynamic performance. Five 3D printed models incorporating geometric variations were fabricated to evaluate their aerodynamic efficiency. Experimental observations showed that models featuring variable chord\, sweep\, and anhedral/dihedral configurations achieved the lowest descent velocities\, underscoring the importance of structural morphology in enhancing autorotative performance. To examine local flow physics in detail\, a custom low-Reynolds-number vertical wind tunnel was developed and characterized. Flat-plate airfoils were studied using Particle Image Velocimetry (PIV) across a wide range of angles of attack and Reynolds numbers\, revealing flow regimes ranging from steady attached flow to unsteady vortex shedding. Wake flow physics of samaras were further captured within a transparent glass chamber using seeded PIV\, revealing stable wingtip vortices extending several diameters downstream and confirming the presence of a windmill-brake state analogous to helicopter autorotation. Induced velocities computed using Momentum Theory showed close agreement with theoretical predictions. To evaluate practical feasibility\, a bioinspired delivery system was designed and tested through drone-based release experiments. Six models (FR01 to FR06) were fabricated and deployed under varying payloads and wind conditions. All models demonstrated successful autorotation and stable descent\, confirming the viability of samara-inspired mechanisms for passive aerial delivery. This research advances the understanding of samara aerodynamics and opens pathways for bioinspired applications in unmanned aerial systems. Future work should explore 3D motion capture\, high-fidelity simulations\, and optimization of geometries and materials. The insights from this thesis provide a strong foundation for future innovations in samara-inspired flight technologies. \nSpeaker :  G.YOGESHWARAN \n  \nResearch Supervisor: Gopalan Jagadeesh \nCo-Research Supervisor: Srisha Rao M V
URL:https://aero.iisc.ac.in/event/ph-d-engg-autorotation-of-single-winged-spinning-samaras/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20251113T110000
DTEND;TZID=Asia/Kolkata:20251113T130000
DTSTAMP:20260907T224720
CREATED:20251112T061505Z
LAST-MODIFIED:20251112T061505Z
UID:10000094-1763031600-1763038800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Aerodynamic Shape Optimization of Low Observable Air Intake Duct : A Gerlach Inspiration
DESCRIPTION:Air intake system supplying air to the aircraft’s propulsion system is an important part of the aircraft. In modern military aircraft\, air intake ducts are bent due to stealth and layout considerations. Due to significant contribution from rotating jet engine components to Radar Cross Section\, need to inhibit direct line of sight of the Engine Face from RADAR’s eye is required and this leads to aggressively turning ducts. Owing to large pressure loss happening due to the secondary flows and consequent flow separation arising out of centrifugal forces or its gradients during flow turns\, total pressure recovery at Engine Face is likely to suffer. This thesis addresses this concern\, specifically for a top mounted serpentine intake duct of flying wing configuration.\n\nA shaping technique called “Gerlach Shaping” proposed by C. R. Gerlach and E. C. Shroeder to minimise secondary flows and subsequent losses forms the core of this thesis. An important feature of the shaping concept is the use of ideal flow assumptions for a flow known to be viscosity driven. As a part of the current research\, formulation and implementation of Gerlach shaping is subject to detailed analysis. Gerlach shaping principles are extended\, opening further possibilities for low loss bend designs. Radial pressure gradients and secondary flow mixing are managed more efficiently leading to smooth flow with reduced flow separation and pressure drops. Superiority of newer designs called “Gerlach Inspired Bend Designs” are proven on a square elbow and RAE M 2129 S-duct. It may be surprising to note that the losses encountered in one of the 90◦ bend designs is even lower than that of a straight duct.\n\nA new methodology called “Gerlach Inspired Duct Optimization” for aerodynamic shape optimization of low observable air intake duct design driven by conflicting aerodynamics and stealth requirements is developed. Understanding of Gerlach shaping principles gained during the evolution of design methodology for low loss bends is a stepping stone to the optimization process. Keeping the spirit of Gerlach Shaping alive\, the highlight of this process is the use of low fidelity inviscid CFD tool for a problem considered to be highly viscous. The step is crucial as integrating CFD simulations with Gerlach Shaping as against ideal flow assumptions would considerably improve the accuracy of the flow field description and enhance the duct design. Moreover\, integration of an inviscid solver facilitates robust\, fast generation of flow field and a large number of candidate designs could be analysed. A completely automated Genetic Algorithm based optimization framework integrated with Computational Fluid Dynamics simulations to realize this methodology inspired by\nGerlach Shaping gives substantial performance enhancement as compared to Reference Duct (designed using conventional design methodology) and Gerlach Duct (generated by morphing the reference duct as per Gerlach shaping).\n\nSpeaker : V Valliammai\n\nResearch Supervisor : N. Balakrishnan
URL:https://aero.iisc.ac.in/event/ph-d-engg-aerodynamic-shape-optimization-of-low-observable-air-intake-duct-a-gerlach-inspiration/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20251022T153000
DTEND;TZID=Asia/Kolkata:20251022T170000
DTSTAMP:20260907T224720
CREATED:20251021T110651Z
LAST-MODIFIED:20251021T110651Z
UID:10000091-1761147000-1761152400@aero.iisc.ac.in
SUMMARY:Ph.D.(Engg):Elastic Wave Propagation in Textured Polycrystalline Media
DESCRIPTION:The performance and reliability of structural components in advanced engineering applications\, such as turbine discs in aeroengines\, are critically influenced by their microstructural characteristics\, particularly the crystallographic texture. Texture controls the mechanical response of a material and ultimately governs the safe life of a component. Ultrasonic non-destructive evaluation (NDE) techniques offer a powerful way to routinely monitor such materials volumetrically; however\, interpreting wave measurements in polycrystalline media is challenging due to structural noise\, wave reflections and mode conversion. While numerical approaches enable the near-experimental exploration of elastic waves in such media\, they are often computationally expensive.\nThis work addresses this challenge by developing a computationally efficient and experimentally supported simulation-driven framework to study elastic wave propagation in textured polycrystalline media and to recover intrinsic material properties\, such as stiffness () and density ()\, from measured group velocities (). The work is structured in two major parts:\nFirst\, forward simulations: Synthetic polycrystalline volume elements (PVE) were generated using DREAM.3D\, subsequently embedded in COMSOL Multiphysics\, where wave propagation studies were conducted on PVEs with controlled texture intensities (e.g.\, Cube {001} <100> and Copper {112} <111>)\, as well as with the experimentally informed microstructures. The results reveal that increasing texture intensity leads to more anisotropic group velocity and reduced wave scattering. To efficiently incorporate large experimental orientation datasets obtained from deformation and annealing textures\, a reduced microstructural strategy was developed that preserves the texture information while significantly reducing computational cost. This approach provides experimental support for the small-sized PVEs\, demonstrating their reliability in capturing the sense of the wave velocity governed by crystallographic texture.\nBuilding upon the methodology developed\, an application-based study was conducted on the dual-microstructure of the turbine disc to investigate the combined effects of grain size and grain orientation on wave velocity. The results showed the dominance of grain orientation over grain size\, establishing texture as a crucial microstructural feature that governs elastic wave propagation and is also a prime indicator of the operational reliability of a component.\nSecond\, inverse property identification: A frequency-domain inversion framework based on spectral finite element method (SFEM)\, and nonlinear least square optimization was formulated to estimate elastic stiffness () and density () directly from the measured wave responses. This approach bypasses time-domain complexities and avoids dependence on prior material data\, achieving accurate recovery of intrinsic properties even in the presence of scattering noise.\nThe inversely predicted data () were validated for both synthetic and experimentally informed microstructures using a wave-independent methodology () that displays an excellent agreement within  4 % deviations. The results reveal how texture information can be inferred using uncertainty limits  and \, which are strongly influenced by microstructural scattering.\nOverall\, the work establishes a computationally efficient and experimentally supported pathway for texture-sensitive applications\, offering a rapid property identification in components where destructive methods are not feasible. These contributions enhance our understanding of wave-microstructure interactions and support the development of routine non-destructive evaluation of structural materials in aerospace and other critical engineering sectors.\n\nSpeaker :  Himanshu Gupta\n\nResearch Supervisors : Prof. S. Gopalakrishnan & Prof. Satyam Suwas
URL:https://aero.iisc.ac.in/event/ph-d-enggelastic-wave-propagation-in-textured-polycrystalline-media/
LOCATION:Auditorium (AE 005)\, Department of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/10/Himanshu.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250718T150000
DTEND;TZID=Asia/Kolkata:20250718T170000
DTSTAMP:20260907T224720
CREATED:20250715T045641Z
LAST-MODIFIED:20250715T045641Z
UID:10000084-1752850800-1752858000@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): ON HIGH-SPEED CURVED COMPRESSION RAMP AIR INTAKES
DESCRIPTION:A scramjet\, i.e.\, a supersonic combustion ramjet\, is an air-breathing engine that enables sustained atmospheric flight in the hypersonic regime. It consists broadly of four key components: the air intake\, isolator\, combustor\, and nozzle. The air intake and the isolator collectively comprise the compression system\, which captures and conditions the freestream flow to suit the operational requirements of the combustor positioned downstream. The general set of attributes sought in a high-speed air intake is: low structural weight; low drag; low aero-thermal loads; started flow with high thermodynamic efficiency and high compression ratio; operational robustness to back-pressure fluctuations arising from the combustor; and stable engine operation over a wide flight envelope. The intake flow characteristics and performance are primarily governed by its geometric shape. High-speed air intakes with a curved compression ramp (CCR) are a class of rectangular intakes wherein the compression ramp comprises a curved surface followed by a planar surface tangential to the trailing end of the curved surface. A CCR intake compresses the flow through a combination of a curved ramp shock wave and a series of compression waves. These intake geometries can provide improvements in compression ratio\, pressure recovery\, and allow for a shorter length intake section in comparison to conventional multi-step intake geometries.\nThe present effort consists of the development of a novel analytical framework to model the CCR intake flow and estimate the intake performance parameters at design and off-design operating conditions\, and wind tunnel experiments with a model CCR air intake at Mach 6 to obtain a detailed understanding of the flow dynamics. The analytical framework builds on the principles of mass conservation and the compressible flow theory to model the inviscid flow structure in the intake without any empiricism. A modified Kantrowitz criterion is proposed to examine the ability of a given fixed-geometry CCR intake to spontaneously self-start at the design Mach number. The framework provides a simple\, fast\, and low-cost tool to develop an effective first-cut design of a self-starting hypersonic CCR air intake for any specified set of operating conditions and performance parameters of interest\, such as the startability\, compression efficiency\, and compression ratio. Inviscid flow numerical experiments of intake starting were carried out to preliminarily verify the starting characteristics predicted by the analytical model.\nThe analytical framework was then employed to identify a suitable geometric design point for the experimental CCR air intake model. A self-starting intake test model was designed following the strong shock design principle\, and built for experimentation in the Roddam Narasimha Hypersonic Wind Tunnel at Mach 6 freestream flow conditions. Time-resolved pressure measurements and high-speed schlieren flow visualization were conducted to understand in detail the flow features internal and external to the intake model\, including the dynamics of shock-shock and shock-boundary layer interactions at the cowl and inside the isolator. Performance assessment at design operating conditions involved evaluating the intake’s ability to spontaneously self-start\, in addition to examining pressure recovery and compression ratio of the started intake. At off-design operating conditions\, the intake dynamics were studied by experimentally varying two parameters: intake back-pressure and angle-of-attack (𝛼). In order to mimic combustor-induced isolator back-pressure variations\, a sliding plate was introduced at the isolator exit; the motion of the sliding plate varies the isolator exit area (blockage) and thereby changes the back-pressure. Experimental results showed that the intake auto-reverts to the started state on realizing suitable pressure values at the isolator exit. Coherent flow oscillations with certain characteristic frequencies were observed in the isolator section during the intermediate state of operation (between started and unstarted states). The angle-of-attack (AoA) studies\, in the 𝛼 range of -70 to 20.70\, show that the relatively gradual distribution of adverse pressure along the compression ramp mitigates the risk of large-scale boundary layer separation\, even at very large AoAs. The model intake was found to satisfy shock-on-lip condition and operate in the started state between 𝛼 = 00 and 𝛼 = 100\, and supersonic flow was sustained in the isolator section up to 𝛼 = 20.70. Overall\, the experimental results were found to validate predictions made by the analytical model. The experiments also allowed for a careful examination of flow during various stages of intake operation\, including intake unstart and restart\, and quantification of operational margins (in terms of pressure) for the model intake. In addition to aiding performance assessment\, these results can also form the basis for the design of a practical early-warning system for preventing engine unstart.\nIn summary\, this work offers a clear experimental demonstration of the advantages offered by CCR air intakes\, and an analytical framework that serves as a good starting point for a design exercise. In practical terms\, this work exhibits the promise held by CCR air intake in providing a wide flight envelope for an air-breathing hypersonic flight vehicle. \nSpeaker : Sushmitha Janakiram \nResearch Supervisor : Duvvuri Subrahmanyam
URL:https://aero.iisc.ac.in/event/ph-d-engg-on-high-speed-curved-compression-ramp-air-intakes/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/07/Sushmitha-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250619T150000
DTEND;TZID=Asia/Kolkata:20250619T170000
DTSTAMP:20260907T224720
CREATED:20250616T090019Z
LAST-MODIFIED:20250616T090019Z
UID:10000080-1750345200-1750352400@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Compressive behavior of continuous fiber polymer composites in the presence of process-induced defects
DESCRIPTION:The current work examines how process-induced defects influence the compressive behavior of composite structures. The defects analyzed include wrinkles at the macroscale and fiber misalignment at the microscale. Uni-directional carbon fiber-reinforced polymer composites with intentionally created wrinkles were produced by strategically positioning laminate strips. Through comprehensive experimental characterization\, the research thoroughly investigates the impact of wrinkle characteristics and their locations on compressive strength and failure modes. Furthermore\, the study explores how these wrinkle features affect the final kink bandwidth\, angle\, and inclination. Fractographic analysis of the failed specimens identified several damage modes across different length scales\, such as kinking\, delamination\, buckle delamination\, crushing\, fiber pullout\, matrix cracking or failure\, and fiber failure. These findings highlight the importance of considering the geometry of the wrinkles and the various damage modes at different scales when creating a numerical model to accurately predict the compressive behavior of the composite.\nUtilizing the damage modes identified through experimentation\, a three-dimensional repeating unit cell framework is used to investigate how various competing damage mechanisms—such as fiber failure\, matrix plasticity and cracking\, and fiber/matrix debonding—impact the compressive behavior of the composite material. A series of parametric studies is performed to evaluate the effects of factors like fiber volume fraction\, fiber misalignment\, and interfacial properties (including strength\, fracture energies\, and friction) on compressive performance. The results reveal a strong correlation between compressive strength and kink band characteristics with fiber volume fraction\, fiber misalignment\, interfacial shear strength\, interfacial friction\, and matrix cracking. This highlights the necessity of accurately characterizing the mechanical properties and geometric features of the composite constituents.\nTo account for the impact of realistic microstructures on compressive behavior\, a two-step homogenization process has been proposed to reduce computational demands and improve the efficiency of the numerical model. In the first step\, the model captures the homogenized elastic properties and longitudinal compressive behavior. These properties are then used as inputs for a model that consists of multiple domains discretized with Voronoi polygons\, each assigned a specific initial fiber misalignment angle based on a statistical distribution. The homogenized compressive behavior has been validated against previous studies and shows strong agreement. Additionally\, the proposed method has the potential to develop into a multiscale modeling strategy that predicts compressive behavior by considering variations in realistic microstructural characteristics. \nSpeaker:  Shashidhar K \nResearch Supervisor : Prof. Kartik Venkatraman (on behalf of Prof Suhasini Gururaja)
URL:https://aero.iisc.ac.in/event/ph-d-engg-compressive-behavior-of-continuous-fiber-polymer-composites-in-the-presence-of-process-induced-defects/
LOCATION:AE Auditorium
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/06/Shashidhar-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250423T100000
DTEND;TZID=Asia/Kolkata:20250423T130000
DTSTAMP:20260907T224720
CREATED:20250422T055303Z
LAST-MODIFIED:20250422T055303Z
UID:10000071-1745402400-1745413200@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Navigation of Autonomous Vehicles using Event Cameras and Modified RRT Methods
DESCRIPTION:Autonomous vehicles\, such as unmanned aerial vehicles (UAVs) and autonomous mobile robots (AMRs)\, are at the forefront of technological innovation and are widely used across various applications. As these vehicles become more agile and operate primarily in unstructured environments\, the components of the navigation pipeline must function in real time while optimizing limited onboard computing and memory resources. The challenges faced by a fast-moving vehicle in indoor environments differ significantly from those encountered by outdoor systems. This thesis focuses on autonomous vehicles operating in indoor\, GPS-denied\, and unstructured environments. The algorithms presented address these specific challenges and contribute to the growing body of research on real-time navigation solutions for such scenarios. In this thesis\, we have investigated and addressed various aspects of the autonomous vehicle navigation pipeline. A key focus throughout the work is ensuring real-time performance on edge computing systems. Inspired by the emergence of bio-inspired event cameras\, which offer potential solutions to the limitations of current state-of-the-art algorithms\, the first part of the thesis explores the use of these sensors for perception tasks such as localization and obstacle avoidance. Event cameras provide several advantages\, including motion blur-free data output\, a high dynamic range\, and enhanced low-light sensitivity. These features make them particularly suitable for improving Visual-Inertial Odometry (VIO) systems over traditional frame-based cameras. However\, the sparse and asynchronous nature of event data poses challenges for conventional computer vision algorithms. Existing approaches often convert event streams into image-like representations\, limiting the full potential of event cameras. To overcome these challenges\, asynchronous (data-driven) methods are essential for event-camera-based VIO solutions. The work here introduces an end-to-end data-driven event camera-based Visual-Inertial Odometry (AeVIO) algorithm that updates the system state based on camera velocity. The algorithm performs event feature detection and tracking asynchronously from the event stream and integrates these measurements with IMU data using a structureless Extended Kalman Filter (EKF) to refine state estimates. Given that the data rate of event cameras depends on the scene texture and the relative motion between the object and the camera\, we also explore their application for high-speed obstacle avoidance. Time-to-contact (TTC) is a critical measure estimating the time before collision if the current motion remains unchanged. While event cameras excel at capturing small\, rapid changes\, they lack the detailed scene information that depth cameras provide. We present a novel approach to fuse the low temporal resolution data from a depth camera with the high-speed output of an event camera to compute TTC with obstacles. The proposed algorithm is integrated into the AirSim simulator and evaluated across various dynamic obstacle scenarios\, demonstrating its effectiveness in collision avoidance. The second part of this thesis focuses on the path planning component of the autonomous navigation pipeline. Effective navigation for AMRs and UAVs requires advanced path planning that accounts for kinematic constraints and enables smooth trajectory execution in complex\, cluttered environments. We investigate a probabilistic framework based on the Rapidly Exploring Random Tree (RRT) algorithm\, which incorporates vehicle kinematics to identify the most likely direction for the next node generation. This approach utilizes Gaussian Mixture Models (GMMs) to improve node generation efficiency while addressing optimization challenges in both 2D and 3D spaces. This acts as dynamic bias in the algorithm. Additionally\, we introduce a next-node selection heuristic that directs the search tree expansion toward the goal while avoiding obstacles. To enhance convergence\, we explore methods to discretize both the action and search spaces. Initially\, the method is applied to AMRs and is subsequently extended to the more complex task of 3D path planning for UAVs. In summary\, this thesis contributes to the navigation pipeline by developing simple\, computationally efficient algorithms that leverage event sensors and probabilistic methods. These algorithms are designed to operate in real-time on modern UAVs and AMRs while preserving their agility\, enabling operation in indoor GPS-denied environments\, and accommodating limited onboard computing resources. \n  \nSpeaker: Ankit Gupta \nResearch Supervisor: Debasish Ghose
URL:https://aero.iisc.ac.in/event/ph-d-engg-navigation-of-autonomous-vehicles-using-event-cameras-and-modified-rrt-methods/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/04/Ankit-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250416T150000
DTEND;TZID=Asia/Kolkata:20250416T170000
DTSTAMP:20260907T224720
CREATED:20250407T063952Z
LAST-MODIFIED:20250407T101249Z
UID:10000068-1744815600-1744822800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Behaviour Modelling of Non-Cooperative Space Objects and Strategies for Decision Support in Space Situational Awareness
DESCRIPTION:In this modern era\, Space is vital for a Nation’s prosperity and without space\, many critical functions would simply stop working. The increasing number of satellite launches in recent times\, is congesting the space environment. Space is also becoming an increasingly contested environment from the perspective of non-civilian applications of satellites. The civilian and non-civilian space applications mandatorily require a complete awareness of the space environment before taking any operational decisions. Space Situational Awareness [SSA] is the comprehensive knowledge of Resident Space Objects [RSOs] which may include satellites\, rocket bodies\, debris\, and the ability to track and understand their behaviour. Space objects can be majorly categorized into two broad types\, cooperative space objects and non-cooperative space objects. A noncooperative space object is defined as a non-friendly object in space and can be perceived as a threat if it performs anomalous maneuvers in space. Modelling pattern-of-life of non-cooperative space objects is an essential requirement of SSA. Maneuvers of non-cooperative satellites is an important event of interest in their life pattern. In this thesis\, we investigate the behaviour of various classes of satellites through data driven modelling. We also study the threat perception from non-cooperative space objects to space assets of our interest. There are four key areas\, in which the thesis has significantly contributed. The first area deals with investigating\, exploring and modelling pattern-of-life of non-cooperative space objects. We have crafted data-driven solution methodologies from time series analysis\, machine learning\, deep learning to suit specific requirements. The second area pertains to the maneuvers of non-cooperative space objects. Identifying them\, helps in analyzing their behaviour. Since there may be numerous non-cooperative space objects and not all maneuvers of non-cooperative space objects may be threatening in nature\, it is essential to segregate routine maneuvers needed by a satellite to maintain its orbit from anomalous and abnormal maneuvers which may be perceived as threat. In this thesis\, we designed an approach to segregate benign and regular pattern-of-life maneuvers of non-cooperative space objects from their orbital data . The routine pattern-of-life maneuvers of satellites are events of interest\, but are infrequent and hence the non-maneuver class was observed to be far more numerous than the maneuver class label in the dataset. Through this thesis work\, we have applied Synthetic Minority Oversampling Techniques (SMOTE) and its variants to handle the imbalance in dataset available for classification. Different missions of cooperative civilian satellites in Low Earth Orbit (LEO) space regime were evaluated to prove the efficacy of the approach. The third area of contribution is in developing methodologies to estimate the threat perception for Geostationary Orbit (GEO) space regime. Modelling pattern-of-life of non-cooperative GEO satellites helps to identify anomalous behaviour and is essential for SSA. Additionally\, given a satellite of interest\, an assessment of the area of influence of neighbourhood satellite operations is critical for assessment of threat. Nearest neighbour search is a fundamental problem in computational geometry and we studied two major concepts of computational geometry \, the Voronoi diagram and the Delaunay triangulation in detail and crafted algorithms to assess threat in the GEO space regime. The last area of contribution is with scheduling the limited and costly ground based sensors to monitor the large number of space objects. There exists a problem of gaps in the available orbital data of noncooperative satellites. Moreover\, the satellite maneuver (event of interest) occurrence information of some samples may be lost\, due to noise in the ground sensor observations or due to observation window limits or losing tracks. Conventional machine learning regression methods are not suited to be able to include both the event and time aspects as the outcome. The conventional models are also are not equipped to handle censored examples (incomplete data due to non-observability). Therefore\, in this thesis\, we devised a solution methodology by applying Time-to-Event data analysis (survival analysis) techniques to assess whether a satellite maneuvered\, that is whether the event of interest occurred or not\, and also estimate when the next maneuver would occur. We have explored a variety of approaches including Cox proportional hazards model\, Weibull distribution model\, Kaplan-Meier model\, Nelson-Aalen model\, Random survival forest\, Survival Support Vector Machines\, Gradient boosted survival analysis and Deep learning based survival analysis. Detailed experimental results based on real life satellite orbital datasets are presented to bring out the effectiveness of the solution methodology. To summarize\, the thesis contributes by developing a space situational awareness system to achieve behavioural modelling\, classification and characterization of space objects of interest\, maneuver classification\, anomaly detection and threat assessment through data driven methodologies. \n  \nSpeaker: Shiv Shankar S  \n  \nResearch Supervisor: Debasish Ghose
URL:https://aero.iisc.ac.in/event/ph-d-engg-behaviour-modelling-of-non-cooperative-space-objects-and-strategies-for-decision-support-in-space-situational-awareness/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/04/SHIV-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250404T110000
DTEND;TZID=Asia/Kolkata:20250404T130000
DTSTAMP:20260907T224720
CREATED:20250403T043429Z
LAST-MODIFIED:20250407T044613Z
UID:10000067-1743764400-1743771600@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Control of Alternating Flow Phenomena in Transonic Shock Wave Boundary Layer Interactions Over Payload Region of a Generic Launch Vehicle Model
DESCRIPTION:The transonic Mach number regime is a critical phase in the atmospheric ascent of launch vehicles\, where aerodynamic loads peak due to the combined effects of high freestream dynamic pressure and angle of attack. Besides high steady loads\, launch vehicles experience very high levels of pressure fluctuations caused by interactions between the unsteady λ-shock system and the boundary layer – a phenomenon known as Shock Wave Boundary Layer Interaction (SWBLI). These interactions can induce buffet excitation over the payload region\, leading to structural failure as well as control issues. NASA recommends limiting the nose cone semi-angle to 15° to mitigate shock oscillations\, labelling such designs as “Buffet-Proof.” However\, practical constraints such as payload mass & volume\, rocket diameter\, launch-pad limitations\, etc. necessitate the use of larger nose cone angles which are buffet-prone. While SWBLI has been well understood for two-dimensional flows\, data for three-dimensional launch vehicle type configurations is sparse in the literature\, with regard to even the basic understanding of the phenomena. Hence\, there is a need to develop physics-based models to handle SWBLI in practical cases.\nWind tunnel experiments were conducted to evaluate the aerodynamic impact of increasing nose cone angles to 20° and 25° in the transonic Mach number range. These investigations revealed critical flow characteristics such as abrupt jumps in pitching moments at small angles of attack (±4°)\, very high levels of pressure fluctuations\, λ-shock system oscillations\, and the occurrence of destabilizing counter-rotating vortices\, intermittent supersonic and subsonic flows (termed alternating flow phenomena) at specific Mach numbers of 0.90 and 0.94. The present research explores two approaches towards controlling SWBLI. The first involves a passive device\, a front-mounted Aerodisc\, systematically evaluated for the effect of geometric parameters at critical Mach numbers of 0.9 and 0.94 in the range of angles of attack of ±4°. The optimized Aerodisc configuration achieved the maximum noise reduction of 22 dB (Overall Sound Pressure Level\, OASPL). The second approach involves an active flow control technique using a pneumatic counterflow jet. The jet parameters were varied during the tests. Jets with exit diameters of 3 mm and 4 mm operating at a pressure ratio of 3.2 achieved the greatest suppression by nearly 20 dB. Both the passive and active techniques demonstrated that by energizing the boundary layer\, the oscillating shock waves were stabilized\, the counter-rotating vortices removed\, and the upstream travelling Kutta waves associated with the alternating flow phenomena completely suppressed.\nThis research clearly brings out the basic physics of SWBLI and its control for 3-dimensional launch vehicle type configurations at transonic Mach numbers\, highlighting that energizing the boundary layer is the key to control the transonic flow over launch vehicles with large blunt nose-cones. \n  \nSpeaker: Dheerendra Bahadur Singh \n  \nResearch Supervisor: Prof. G. Jagadeesh
URL:https://aero.iisc.ac.in/event/ph-d-engg-control-of-alternating-flow-phenomena-in-transonic-shock-wave-boundary-layer-interactions-over-payload-region-of-a-generic-launch-vehicle-model-2/
LOCATION:CEH Conference Hall- Room No.239\, Second Floor\, Department of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/04/Dheerendra-.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250319T150000
DTEND;TZID=Asia/Kolkata:20250319T170000
DTSTAMP:20260907T224720
CREATED:20250313T105656Z
LAST-MODIFIED:20250326T050053Z
UID:10000063-1742396400-1742403600@aero.iisc.ac.in
SUMMARY:MTech(Res) : Elastic Wave Dispersion Analysis and Mode Shape Investigation of Higher-order Beam Theory for Thick Beams
DESCRIPTION:The dynamic behavior of structural components over broad frequency ranges\, particularly thick beams under different constraints\, is important in many engineering applications where reduced dimensional modeling is required for design. Applications are aerospace structures\, mechanical systems and civil infrastructure. The rigid cross-section assumption in Euler-Bernoulli and even third-order beam theories cannot accurately capture the effects of stress-free or finite surface conditions and higher-order stress distribution under dynamic situations. While some higher-order beam theories satisfy shear stress boundary conditions\, they do not fully account for normal stress. The higher-order beam theory employed in this study addresses these limitations. It satisfies both shear and normal traction conditions simultaneously. Another problem in guided wave behavior within thick beams is accurately modeling consistent surface or interior dynamics. For this\, the transverse displacement is approximated using a trigonometric variation across the thickness\, characterized by a fundamental wave vector consistent with the necessary stress variation throughout the thickness\, which is particularly relevant for thick structures.\n\nThere remains a lack of comprehensive comparison between different reduced-order models\, particularly in terms of their accuracy in predicting wave dispersion characteristics and dynamic deformation mode shapes in the short and long wavelength limits to evaluate the acceptability of specific models in specific applications. Also\, the choice of beam theory directly influences these properties. This study compares four different theories: Euler-Bernoulli\, Timoshenko\, Third-order shear\, and proposed higher-order theory with surface constraints. The dispersion characteristics of each beam theory are obtained by solving the characteristic equations using the polynomial eigenvalue method\, and dispersion curves are plotted to compare wave propagation behavior predicted by different theories. This comparison highlights the limitations of the lower-order theories\, especially in their ability to accurately capture the behavior of thick beams\, and demonstrates how higher-order theory provides improved predictions of wave behavior.\n\nTwo numerical validation techniques are employed to validate and investigate higher-order wave modes present in higher-order beam theory: one is based on the two-dimensional Fast Fourier Transform (2D FFT)\, and the other uses particle displacement vector plots. In the first approach\, a time-varying excitation is applied to the beam with a specific tonal frequency\, and time-domain response data is collected. The 2D FFT is then performed to extract the dominant wave modes. This method generates the flexural and axial modes at 300kHz frequency as an example\, which is better predicted using the higher-order beam theory. In the second approach\, wave motion is visualized as particle trajectories by plotting displacement components along axial and transverse directions. This method enables the generation of pure wave modes by solving the displacement field directly\, eliminating dependencies on boundary conditions and external excitation. This method validates all mode shapes present in the Higher-order beam theory.\n\nIn summary\, this thesis presents a comparative study of various beam theories to highlight the importance of higher-order beam theories where relevant physics needs to be captured. The dynamic effects are relevant in applications in vibrating machinery\, dynamic contact effects\, bearings\, and advanced contact force-based testing like resonance and force microscopy.\n\n\nSpeaker : Kratika Raje\n\nResearch Supervisor: Prof. D. Roy Mahapatra
URL:https://aero.iisc.ac.in/event/mtechres-elastic-wave-dispersion-analysis-and-mode-shape-investigation-of-higher-order-beam-theory-for-thick-beams/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/03/Kratika-1-1.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250318T110000
DTEND;TZID=Asia/Kolkata:20250318T130000
DTSTAMP:20260907T224720
CREATED:20250311T060827Z
LAST-MODIFIED:20250311T060827Z
UID:10000060-1742295600-1742302800@aero.iisc.ac.in
SUMMARY:Ph.D.(Engg): Investigations on Hypersonic Laminar to Turbulent Boundary Layer Transition in a Shock Tunnel.
DESCRIPTION:The laminar to turbulent boundary layer transition onset has perplexed fluid dynamics community irrespective of the flow regime under which the phenomenon is probed. The complexity of the problem is compounded in high-speed compressible flows where in the transition onset location is a strong function of many subtle factors like freestream quality\, surface roughness\, wall temperature etc. The transitional and turbulent boundary layers bring their typical characteristics\, like an increase in skin friction\, heat transfer\, fluid dynamic parameters fluctuations\, mixing characteristics\, potential to negotiate adverse pressure gradient\, along with them. These typical characteristics of transitional and turbulent boundary layers can be both detrimental and advantageous to a given facet of an aerodynamic vehicle design. Hence the boundary layer transition onset location is one of the key design inputs in the development of aerodynamic vehicles operating in subsonic\, supersonic and hypersonic freestream environment. A plethora of work has been conducted to investigate the transition onset phenomena in supersonic and hypersonic flow regime since the beginning of space age and the inception of the idea of an air breathing hypersonic cruise vehicle. The outcomes of these investigations and studies on high-speed boundary layer transition onset although led to the development of several techniques and correlations to estimate the transition onset location\, applicable usually to a particular test model and freestream condition\, very few studies targeted the characterization of transitional boundary layer in hypersonic flow regime. The earlier and contemporary work on roughness induced transition onset focused on the effect of the said roughness element on transition onset location but the features associated with the instabilities thus generated by these roughness elements have seldom been reported in the open literature. Hence characterization of transitional boundary layer and the instabilities associated with the same was one of the primary objectives of the present work.\nThe present work on hypersonic boundary layer transition was conducted in a shock tunnel HST4 by employing generic test models like flat plate\, cone and elliptic cone. The work began with the design\, development and deployment of a new contoured nozzle\, with a nominal Mach number of 6.0\, for HST4. Before embarking on the boundary layer transition studies\, dedicated efforts were made to characterize the freestream noise environment of the test section of HST4 by employing experimental and numerical methods. A two-dimensional finite difference Navier-Stokes solver was developed in order to numerically compute the transfer functions required to retrieve freestream pressure fluctuations from the experimental measurements. The RMS of pressure fluctuations in the test section of HST4 was found to be 4.32% for the freestream Reynolds number of 4.5 million/m with major contribution of low frequency fluctuations (<50 kHz) towards the aforementioned RMS magnitude. The transitional boundary layer on smooth surface of a flat plate and an axisymmetric cone were characterized by experimentally measuring the intermittency associated with such boundary layers. The intermittent nature of the transitional boundary layer results from the convection of the turbulent spots along the boundary layer. The leading edge and trailing edge velocities associated with these turbulent spots as well as their generation rates were experimentally measured and computed. The second mode instabilities\, a typical characteristic of high Mach number boundary layers\, were also measured in terms of pressure fluctuations and the bandwidth of these instabilities was found to be in the range of 240-480 kHz. The wavelengths associated with these instabilities were found to be 2.5 times the local boundary layer thickness. Transition onset due to the presence of an isolated roughness element\, either a protrusion or a three-dimensional shoe box cavity\, was also investigated as part of the present campaign. Both isolated protrusion and cavity led to an early onset of transition when compared to the smooth test models with no isolated roughness element. In the case of transition onset due to an isolated cubic protrusion\, the Shuttle Orbiter correlations were found to be inadequate in estimating the transition onset and correlations based on the present dataset were formulated. A single frequency oscillation with a narrow bandwidth centered around 23 kHz corresponding to hair pin vortices in the wake of roughness element was found in the present work. It was also found that while the protrusion suppressed the second mode instabilities\, the cavity aided in the development of high frequency instabilities akin to second mode. Finally initial findings of the transition onset due to cross flow instabilities in an elliptic cone were also discussed in the present work. \n  \nSpeaker : Ankit Bajpai \n  \nResearch Supervisor : Prof. Gopalan Jagadeesh
URL:https://aero.iisc.ac.in/event/ph-d-engg-investigations-on-hypersonic-laminar-to-turbulent-boundary-layer-transition-in-a-shock-tunnel/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2025/03/Ankit-.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20250313T150000
DTEND;TZID=Asia/Kolkata:20250313T170000
DTSTAMP:20260907T224720
CREATED:20250311T110524Z
LAST-MODIFIED:20250311T110524Z
UID:10000061-1741878000-1741885200@aero.iisc.ac.in
SUMMARY:Ph.D.(Engg) : Effect of Laser Shock Peening on Residual Stress and Mechanical behaviour of Aluminium alloy AA2219 Friction Stir Weld
DESCRIPTION:Aluminium alloy AA2219 is a precipitation hardenable wrought alloy with copper as a major alloying element. Large-volume propellant tanks of space launch vehicles are manufactured by joining AA2219 aluminium alloy through Friction Stir Welding (FSW) and it is designed optimally to improve the payload capability.  An increase in the strength of the FSW joint results in payload improvement of space launch vehicles. Residual stress is one of the crucial parameters for the design of pressure vessels\, and it is also necessary to mitigate or reduce the same to improve structural margins. The main challenge is understanding the cause of residual stress\, its evaluation\, and mitigation due to the FSW process. Laser shock peening (LSP) is one of the most promising surface modification techniques to improve the performance of weld joints. In the LSP process\, a high-energy laser beam impacts the surface of the specimen and generates ionized plasma by evaporating a thin ablative layer on the specimen. When a high-energy laser pulse passes through the transparent layer and hits the sample\, the thin ablative layer is vaporized and continues to absorb the laser energy resulting in the generation of ionized plasma. Rapidly expanding plasma is entrapped between the specimen and the transparent layer\, generating high surface pressure and propagating into the sample as a shock wave. When the peak pressure exceeds the material’s yield strength\, plastic deformation occurs in the specimen.\n\nThe present work aims to investigate the impact of LSP on residual stress\, microhardness\, global tensile behaviour\, tensile behaviour of various zones (local tensile behaviour)\, stress corrosion cracking behaviour and surface roughness of AA2219 T87 FSW. Surface and through-thickness residual stress were investigated in this work. In as-welded conditions\, tensile residual stress exists in the weld region with a peak value of +123.5 MPa in the Thermo-Mechanically Affected Zone (TMAZ). LSP has significantly affected all the regions of the weld and reduced tensile residual stress to compressive. Longitudinal residual stress is non-uniform through thickness as well as across the weld. Peak tensile residual stress is +160 MPa at the centre of the weld in mid-thickness\, and the LSP process led to a 55% reduction.\n\nAA2219 T87 FSW exhibits a yield strength of 197 MPa and an ultimate tensile strength of 348 MPa at ambient temperature. The LSP process increased the yield strength of the FSW joint by 7 – 14%. A similar increase is seen in cryogenic temperatures also. The increase in the yield strength is due to the strain-hardening effect induced by LSP. The response of different zones of FSW to tensile lading and LSP was investigated using the digital image correlation technique. LSP led to an increase in YS in Weld Nugget and TMAZ. However\, HAZ does not exhibit a significant increase in YS. The LSP process led to an increase in microhardness of 7 – 20%. Single-layer peening has affected < 0.5 mm depth\, whereas three and six layers of peening have influenced a depth of 1.0 mm and more than 2 mm\, respectively. Metallographic study of LSP specimen confirms an increase in dislocation density\, which is the cause for the increase in YS and microhardness.  The LSP process has increased surface roughness in all regions of FSW\, and the increase is substantial in the weld nugget and TMAZ regions. The LSP process has not affected stress corrosion cracking resistance\, irrespective of the number of layers of peening.\n\nIn summary\, a systematic investigation of the effect of LSP on AA2219 T87 FSW joint is carried out using various experimental and characterization techniques and the benefits of LSP are clearly brought out. LSP of AA2219 FSW reduces tensile residual stress and increases YS. This study has also quantified the improvement in YS of various zones of AA2219 FSW due to the LSP. An increase in microhardness was also noticed due to LSP. In addition\, resistance to stress corrosion cracking is not compromised due to LSP. This research outcome will be useful in improving the structural safety margin or reducing the inert mass of aerospace structures and pressure vessels.\n\n\nSpeaker : Dhanasekaran M P\n\n\nResearch Supervisor: Prof. D. Roy Mahapatra
URL:https://aero.iisc.ac.in/event/ph-d-engg-effect-of-laser-shock-peening-on-residual-stress-and-mechanical-behaviour-of-aluminium-alloy-aa2219-friction-stir-weld/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
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DTSTART;TZID=Asia/Kolkata:20250312T150000
DTEND;TZID=Asia/Kolkata:20250312T170000
DTSTAMP:20260907T224720
CREATED:20250307T064034Z
LAST-MODIFIED:20250307T064034Z
UID:10000059-1741791600-1741798800@aero.iisc.ac.in
SUMMARY:Ph.D.(Engg) : Multi-Agent Pursuit-Evasion and Coverage Strategies
DESCRIPTION:Autonomous agents are increasingly being used to solve many tasks\, deemed complex by humans\, with ease and effectiveness. Two such applications are in defense scenarios and in coverage. This thesis\, therefore\, is devoted towards study of motion planning strategies for autonomous agents in the context of pursuit-evasion problems as well as different coverage problems. The thesis comprises two parts. In the first part\, pursuit-evasion is considered between an evader and one or more pursuers\, all the agents being non-holonomic having turn radius constraints. A partial information setting is considered wherein the agents (evader and pursuer) know about each others’ speed and position but not about their turning capability. The objective in these problems\, where the pursuer is of higher speed but less agile\, is to obtain an evasive strategy. A two-phase evasive strategy is proposed as an effective solution against the pursuers. It is a proximity based strategy. In the first phase\, when the pursuer is beyond a critical distance from the evader\, the latter assumes the worst that the pursuer is holonomic and solves for the best response strategy. This phase is called the Worst Case Scenario Planning (WCSP). When the evader is within the critical range from the pursuer\, the former attempts sharp maneuvers to sidestep the pursuer and extend time of capture. This phase is called the Proximity Based Maneuver (PBM). Dynamic programming is used to solve for the WCSP strategy. In case of multiple pursuers\, the concept of dominance regions is used to obtain the WCSP strategy. Additionally\, the pursuit-evasion problem is extended to a reach-avoid problem where the evader has the dual objective of avoiding the pursuer and reaching a target. This thesis considers the problem of reaching a moving but non-maneuvering target by a turn radius constrained evader in the shortest time. The evader is modeled as a Dubins vehicle and the reaching strategy is deduced by studying the time-to-go properties for different strategies and chronologically checking simple conditions at crossover points. The proposed two-phase evasive strategy is used for avoiding the pursuer. The reaching strategy and the avoiding strategy are linearly combined to obtain the net reach-avoid strategy. Extensive simulation results are provided to corroborate the effectiveness of both the evasive and the reach-avoid strategies. In the second part of the thesis static and dynamic coverage problems are discussed. Inspiration from flocking principles with substantial modifications is used to design a static coverage strategy. This ensures that the covering agents are spread uniformly around the structure while avoiding collision among themselves and with obstacles in the environment. Coverage is addressed for convex and non-convex shapes in 2D and 3D. For dynamic coverage\, concept of Lissajous curves is used to achieve coverage. Dynamic coverage is split into two chapters: coverage of planar regions and coverage of 3D structures. For planar regions\, the boundary of the region is approximated using Fourier series and radial Lissajous curves are generated within the boundary as reference coverage paths. The optimal field-of-view size is analytically determined along with the upper-bound on the time taken for complete coverage. Various extensions of the strategy such as preferential coverage and simultaneous coverage are also discussed. For 3D structures\, an enclosing volume is considered and Lissajous curves are generated on the surface of the enclosing volume. Conditions for complete coverage as well as collision free coverage in case of multiple agents are determined analytically. Artificial potential fields are used to obtain coverage by conforming to shape of the structure. A variety of enclosing volumes are discussed along with diverse applications such as patch coverage\, waypoint coverage\, and coverage of moving structures. Performance metrics are proposed for both static and dynamic coverage problems that helps in ascertaining the quality of coverage. \n  \nSpeaker : Suryadeep Nath    \nResearch Supervisor: Debasish Ghose
URL:https://aero.iisc.ac.in/event/ph-d-engg-multi-agent-pursuit-evasion-and-coverage-strategies/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
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