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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:20240101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20241203T110000
DTEND;TZID=Asia/Kolkata:20241203T130000
DTSTAMP:20260824T061849
CREATED:20241126T095210Z
LAST-MODIFIED:20241129T054751Z
UID:10000033-1733223600-1733230800@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Aeroacoustic sources in twin turbulent jets
DESCRIPTION:An understanding of the aeroacoustics of twin turbulent jets is essential for applications involving noise reduction in dual engine aircrafts and launch vehicles. The aeroacoustic dynamics of these jets are influenced by the spacing between the shear layer of the two jets as well as the spatio-temporal nature of the structures arising from the interaction between the two jets. In the present work\, we construct reduced-order models of aeroacoustic sources for single and twin subsonic jets ($M_j=0.9$\, $Re=3600$)\, with the individual jets being replicas of a single jet\, with the goal of accurately recovering the far-field sound over a rather wide band of frequencies St=[0.07\,1.0] and directivity angles\, phi = [30 deg\,120 deg] within a subdecibel level accuracy. These models are designed as linear combinations of spatio-temporally coherent SPOD modes obtained in terms of the Lighthill’s stress tensor\, which in turn is computed through large-eddy simulations (LES) of the turbulent jets.  The present investigation involves two sets of twin subsonic jets of diameter D each\, with spacings of 0.1D and 1D\, where the jets merge upstream and downstream of breakdown\, respectively.  This is observed to alter the dynamics of twin jet evolution.  The closely spaced twin jet decays the slowest due to reduced turbulent stresses which are\, however\, more broadband due to early merging.  Such jets also show strong shielding in the plane of jets\, especially at shallow directivity angles where sound levels may drop below that of the single jet.  The farther spaced twin jets have dynamics that are more akin to the constituent single jet with turbulent fluctuations peaking here at St=0.34\, but showing very little shielding\, with their OASPL mostly linked to the nature of extra flow structures created during merging.  Three-dimensional\, energy-ranked\, coherent structures (SPOD modes) for twin jets exhibit rather poor low-rank behaviour\, especially\, at the far-field spectral peak St=0.14\, unlike that of the single jet\, which is indicative of spatio-temporally complicated structures arising from the merging of the turbulent merging of the twin jets.  At St > 0.3\, the SPOD wavepackets show strong visual coherence\, resembling Kelvin–Helmholtz instability modes upstream of breakdown\, while at the lower frequencies there is very little spatial coherence with wavepackets peaking downstream of breakdown.  Although the leading SPOD modes radiate poorly\, reduced-order models using a subset of them\, up to 45 SPOD modes per frequency\, show for the first time remarkable match (within 1 dB) against the LES-predicted sound over 0.1 < St < 0.5\, at all angles investigated\, including that for the peak sound. At other frequencies\, the error barely exceeds a decibel\, except for the closely spaced twin jet which due to its greater hierarchy of spatio-temporal structures\, show slower convergence at the shallower angles for St > 0.5. \n  \nSpeaker:  Nishanth Muthichur \nResearch Supervisor: Santosh Hemchandra
URL:https://aero.iisc.ac.in/event/ph-d-engg-aeroacoustic-sources-in-twin-turbulent-jets/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/11/nishant.jpg
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DTSTART;TZID=Asia/Kolkata:20241127T110000
DTEND;TZID=Asia/Kolkata:20241127T130000
DTSTAMP:20260824T061849
CREATED:20241126T094710Z
LAST-MODIFIED:20241126T094710Z
UID:10000032-1732705200-1732712400@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): On the nature of transonic buffet in a finite span wing
DESCRIPTION:Transonic buffet\, or shock oscillations\, is a pre-stall aerodynamic instability\, caused by shock boundary layer interaction\, of the flow over a wing. This aerodynamic instability occurs at critical combinations of transonic Mach number and angle of attack. Shock oscillations cause vibrations of the wing and is known as buffeting. Buffeting may cause fatigue of the wing\, and in an overall sense limit the flight envelope of the aircraft. Despite decades of study\, an unequivocal understanding of the physical mechanism of transonic buffet is lacking. In literature\, global stability analysis\, modal analysis\, and spatial correlation-based wave propagation analysis have been the tools of choice in understanding the mechanisms that cause transonic buffet. Here we present a perspective on transonic buffet\, using results from correlation analysis\, streamwise and spanwise pressure distributions\, and the temporal evolution of skin friction lines on the surface of the Benchmark Supercritical Wing (BSCW). Skin friction lines and critical point theory are well established to describe 3D separated flows over solid walls and bodies. Together with correlation analysis of time-resolved fluid dynamics\, the evolution of skin friction lines reveals a new perspective on the driving mechanism for shock oscillations. This viewpoint supports\, in some ways\, earlier observations on the drivers of shock-induced separation in a finite span and infinite span wing but also reveals new insights on 3D shock oscillations. The presence and distribution of these critical points—unstable foci\, saddle points\, and nodes—lead to the formation of buffet cells or pockets of streamwise shock oscillations along the span. The topology of skin friction lines in the presence of these critical points gives rise to separation and re-attachment lines. In particular\, the propagation of buffet cells is shown to be due to the self-induced motion of contra-rotating unstable foci in the skin friction lines. The self-induced motion of these unstable foci\, or vortices\, causes them to convect inboard or oscillate spanwise. This perspective on transonic buffet based on the distribution of critical points of the skin friction lines\, enables possibilities of buffet control using low-order nonlinear dynamical system models. \nSpeaker: Magan Singh \nResearch Supervisor: Prof Kartik Venkatraman
URL:https://aero.iisc.ac.in/event/ph-d-engg-on-the-nature-of-transonic-buffet-in-a-finite-span-wing/
LOCATION:Online
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/11/magan.jpg
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240917T153000
DTEND;TZID=Asia/Kolkata:20240917T163000
DTSTAMP:20260824T061849
CREATED:20241118T094538Z
LAST-MODIFIED:20241118T094538Z
UID:10000021-1726587000-1726590600@aero.iisc.ac.in
SUMMARY:Advanced Mission Architectures for Long-term Exploration of Mars\, Venus\, and Beyond
DESCRIPTION:The increasing complexity of future space exploration roadmaps calls for novel mission architectures\, integrated mission analysis\, and systems engineering frameworks to inform early decision-making and technological innovation. In this talk\, I will discuss the mission architecture and analysis of two multi-decade campaigns: (1) human missions to Mars\, and (2) astrobiology-driven missions to Venus. First\, I will present the orbital design considerations and results for Mars Spacedock\, an orbital platform for sustainable human exploration. A system-level optimization incorporates discreet mission constraints and comprehensive analysis across all the mission phases from interplanetary trajectories to entry\, descent\, and landing (EDL). Surface accessibility from candidate orbits is obtained by implementing constant bank angle control during EDL. Next\, I will discuss the mission design for a series of missions to Venus searching for signs of life in the clouds. I will highlight the early trade-offs between objectives and operational constraints for a balloon platform and a sample return mission. A focal point will be the Venus ascent vehicle design for sample return through launch trajectory optimization. Additionally\, I will briefly discuss ongoing experiments to establish the feasibility of instruments for in situ analysis of sulfuric acid clouds. Finally\, I will discuss my future research plans in mission design\, systems engineering\, and innovative small-scale spacecraft testing platforms for advanced technologies such as GNC during proximity operations.   \nSpeaker: Dr. Rachana Agarwal \nBiography: Rachana Agrawal is currently a Postdoctoral Associate in the Earth\, Atmospheric and Planetary Sciences department with Prof. Sara Seager at MIT. She is leading mission design and instrumentation projects for astrobiology-focused missions to Venus. She obtained her PhD from the School of Aeronautics and Astronautics at Purdue University under the supervision of Prof. James Longuski and Prof. Sarag Saikia. Her PhD work focused on the design and analysis of an orbital logistics architecture for the sustainable human exploration of Mars. She is broadly interested in robotic and human space mission engineering with current focus on mission analysis\, systems engineering\, and technological innovation and development.
URL:https://aero.iisc.ac.in/event/advanced-mission-architectures-for-long-term-exploration-of-mars-venus-and-beyond/
LOCATION:Online
CATEGORIES:AE Seminar
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2024/04/AE-Seminar.jpg
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