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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
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DTSTART:20260101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260806T113000
DTEND;TZID=Asia/Kolkata:20260806T130000
DTSTAMP:20260828T235826
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
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260807T110000
DTEND;TZID=Asia/Kolkata:20260807T130000
DTSTAMP:20260828T235826
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:20260810T110000
DTEND;TZID=Asia/Kolkata:20260810T130000
DTSTAMP:20260828T235826
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
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260814T110000
DTEND;TZID=Asia/Kolkata:20260814T133000
DTSTAMP:20260828T235826
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
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20260901T140000
DTEND;TZID=Asia/Kolkata:20260901T170000
DTSTAMP:20260828T235826
CREATED:20260825T054145Z
LAST-MODIFIED:20260825T054307Z
UID:10000147-1788271200-1788282000@aero.iisc.ac.in
SUMMARY:Taming Turbulence
DESCRIPTION:Turbulence remains one of the outstanding problems of classical physics\, and one that has challenged physicists and engineers alike for decades\, even centuries. The fusion of classical approaches and tools of the modern day – theoretical analysis of the Navier-Stokes equations\, state-of-the-art experimental observations\, data-driven methods and machine learning – has led to substantial progress towards understanding the mechanisms sustaining turbulence\, developing predictive capabilities and achieving the potentially revolutionary goal of harnessing or taming turbulence in large-scale (high Reynolds number) practical settings. In this talk\, I will describe some fundamental challenges posed by turbulence near walls\, the impact of this phenomenon on many of the world’s pressing scientific concerns\, and some recent advances.\n\n \nSpeaker : Prof. Beverley McKeon\n\nbiography:\n\nBeverley J. McKeon is Professor of Mechanical Engineering at Stanford. She received her B.A.\, M.A. and M.Eng. from the University of Cambridge in the United Kingdom\, and an M.A. and Ph.D. in Mechanical and Aerospace Engineering from Princeton University. She completed postdoctoral research and a Royal Society Dorothy Hodgkin Fellowship at Imperial College London. Best known for her work pioneering resolvent analysis as an equation-driven tool to analyze and predict the dynamics of turbulent flow\, her research group has specialized in addressing its application to understand and modify wall turbulence in numerical data and via experiments with external forcing. Prof. McKeon is a Fellow of the APS and the AIAA and the recipient of a Vannevar Bush Faculty Fellowship from the DoD in 2017\, the Presidential Early Career Award (PECASE) in 2009 and an NSF CAREER Award in 2008 as well as Caltech’s Shair Program Diversity Award\, Graduate Student Council Excellence in Mentoring Award and Northrop Grumman Prize for Excellence in Teaching. She currently serves as co-Lead Editor of Physical Review Fluids and on the editorial board of the Annual Review of Fluid Mechanics.\n \nCoffee/tea will be served after the seminar at 3:30 pm.\n\nAt 4:00 pm\, Prof. McKeon will hold a special session on Physical Review Fluids\, one of the world’s leading research journals for fluid dynamics. Prof. McKeon is the co-Lead Editor of the journal. The session includes a short presentation on the journal’s history\, Q&A\, and a short tutorial on writing a successful submission.
URL:https://aero.iisc.ac.in/event/taming-turbulence/
LOCATION:Auditorium (AE 005)\, Department of Aerospace Engineering
CATEGORIES:AE Seminar
ATTACH;FMTTYPE=image/png:https://aero.iisc.ac.in/wp-content/uploads/2026/08/taming_turbulence_poster_16x9-4.png
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