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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:20260105T110000
DTEND;TZID=Asia/Kolkata:20260105T130000
DTSTAMP:20260430T115537
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:20260116T160000
DTEND;TZID=Asia/Kolkata:20260116T170000
DTSTAMP:20260430T115537
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:20260119T150000
DTEND;TZID=Asia/Kolkata:20260119T170000
DTSTAMP:20260430T115537
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
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