BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Department of Aerospace Engineering - ECPv6.6.3//NONSGML v1.0//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-ORIGINAL-URL:https://aero.iisc.ac.in
X-WR-CALDESC:Events for Department of Aerospace Engineering
REFRESH-INTERVAL;VALUE=DURATION:PT1H
X-Robots-Tag:noindex
X-PUBLISHED-TTL:PT1H
BEGIN:VTIMEZONE
TZID:Asia/Kolkata
BEGIN:STANDARD
TZOFFSETFROM:+0530
TZOFFSETTO:+0530
TZNAME:IST
DTSTART:20260101T000000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20261001T113000
DTEND;TZID=Asia/Kolkata:20261001T130000
DTSTAMP:20261010T051229
CREATED:20260928T090723Z
LAST-MODIFIED:20260929T095847Z
UID:10000154-1790854200-1790859600@aero.iisc.ac.in
SUMMARY:Ph.D. (Engg): Splashing of impacting drops on rigid and flexible superhydrophobic surfaces
DESCRIPTION:Understanding droplet impact dynamics on superhydrophobic (SHP) surfaces is crucial for exploiting their exceptional liquid-repellent properties in various industrial applications. Studies on high-velocity droplet impacts on SHP surfaces\, particularly under splashing conditions\, are of significant importance for applications such as anti-icing and erosion protection of turbine blades. This thesis presents an experimental investigation of splashing of impacting drops on flexible cantilever and rigid superhydrophobic (SHP) surfaces. The SHP surfaces are prepared by spray-coating plastic polymer films (overhead projector sheets) with commercially available NeverWet hydrophobic solution. For the flexible cantilever SHP surfaces\, the coated film is cut into rectangular beams\, with one end of the beam is firmly fixed on an aluminium support. For the rigid SHP surface\, the entire coated film is firmly fixed to the aluminium support. In this study\, four cantilever beams of different lengths are considered to study the effect of beam stiffness on the drop impact dynamics. Three different droplet liquids – water (W)\, 20% glycerine and 80% water (G20)\, and 50% glycerine and 50% water (G50) – varying mainly in their dynamic viscosity are considered.\nWater droplet impact on the rigid superhydrophobic (R-SHP) surface exhibits five regimes with increasing Weber number\, We\, from complete rebound to prompt splashing\, and is mapped on a We–Re chart alongside reported SHP surfaces. The various parameters of droplet impact such as maximum spread factor (βmax)\, spreading time\, contact time\, maximum retraction rate\, and coefficient of restitution (COR) are characterized as functions of We. The splashing of impacting water drops on the R-SHP surface is studied and an additional regime (sixth regime) of prompt splashing with hole nucleation is documented. Quantitative measurements of the temporal variation of lamella diameter\, number of holes formed\, time at which the first hole nucleates\, critical impact velocity at which the hole-nucleation begins\, and contact time are extracted. These measurements clearly show that the contact time reduction of splashing droplets decreases with increase in droplet viscosity. Moreover\, the number of holes formed in the lamella film scales with the number of micro-bumps underneath the droplet at its maximum spreading which\, in turn\, decreases with increase in droplet viscosity. The time instant at which the first hole nucleates on the lamella film is seen to be independent of the droplet viscosity. A modified model is proposed to describe the effects of droplet viscosity and surface micro-characteristics (height and pitch of surface micro-bumps) on the critical velocity for hole nucleation\, Uc\,h. The predictions from this modified model seem to explain the experimental observations on Uc\,h in the current study as well as in the literature.\nDroplet impacts on the flexible superhydrophobic (F-SHP) surface follow the same sequence of regimes as the R-SHP surface\, but the regime boundaries are shifted to higher We due to partial energy transfer from the droplet into beam bending. For a given We\, the maximum spread factor\, receding velocity\, and maximum rebound height are all reduced relative to that of the R-SHP surface. A modified Weber number\, We#\, which accounts for the elastic bending energy stored in the beam during the drop impact dynamics is proposed\, and the variation of F-SHP data with We# collapses with the corresponding data recorded on the R-SHP surface for both spreading and receding dynamics. The beam oscillation response\, including deflection\, oscillation amplitude\, and the effect of droplet re-impact on the oscillation cycle\, is also characterized. Splashing dynamics of impacting drops on the F-SHP surface shows regime transitions comparable to those on the R-SHP surface but shifted to higher We and Re. Hole nucleation on the F-SHP surface is delayed relative to the R-SHP surface. The recorded value of Uc\,h increases from 1.75 to 2.00 m/s (14.3%) for W and from 2.35 to 2.53 m/s (7.7%) for G20 drops\, and the number of holes is lower for both liquids at a given We\, attributed to part of the impact kinetic energy being stored as strain energy in the beam. For G50 drops\, no holes are formed on both surfaces within the tested We range. Before the hole nucleation\, the contact time is unaffected by the surface flexibility\, and while beyond Uc\,h\, the recorded contact time is longer on the F-SHP surface by about 10% for W and 8% for G20 drops. The surface flexibility therefore affects the contact time only indirectly\, by delaying and suppressing hole nucleation.\nThe effect of beam stiffness on droplet impact dynamics is studied by carrying out water drop impacts on four F-SHP surfaces. The maximum spread factor follows βmax = α(We)0.25\, with the empirical constant α decreasing systematically from 1.012 for the stiffest beam to 0.899 for the most flexible beam\, reflecting greater energy loss to beam bending as stiffness decreases. The variation of βmax with We# collapses the data across all the F-SHP and R-SHP surfaces into a single trend\, established in the present study as βmax = α#(We#)0.25 with α# estimated as 1.00 ± 0.07 for both the R-SHP and F-SHP surfaces. Similarly\, the receding velocity decreases with decreasing beam stiffness but collapses across all surfaces when plotted against We#. The contact time is found to be largely unaffected by the beam flexibility. The maximum rebound height of the bouncing drop on the F-SHP surfaces decreases with decreasing beam stiffness. Since the pinched-off droplet formed in the rebounding process carries 6 to 14% of the impacting droplet mass\, the COR is redefined in the present study using an effective rebound velocity that accounts for both droplets\, and the modified COR decreases with increasing beam length at a given We. The maximum beam tip deflection of the F-SHP surfaces increases with both We and beam length\, L\, and is well predicted by spring-mass model incorporating the impact force and beam natural frequency\, fb. Finally\, a theoretical model is proposed to predict COR on the F-SHP surfaces. The proposed model predicts the experimental COR across all F-SHP and the R-SHP surfaces with errors of 5.0 – 15.2% and also captures the dependence of COR on the beam length.\n\nSpeaker : Kumar Gaurav   \n\nResearch Supervisor : D. Sivakumar
URL:https://aero.iisc.ac.in/event/ph-d-engg-splashing-of-impacting-drops-on-rigid-and-flexible-superhydrophobic-surfaces/
LOCATION:STC Seminar Hall\, Dept. of Aerospace Engineering
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/09/Kumar.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20261006T143000
DTEND;TZID=Asia/Kolkata:20261006T170000
DTSTAMP:20261010T051229
CREATED:20261005T050831Z
LAST-MODIFIED:20261005T101944Z
UID:10000155-1791297000-1791306000@aero.iisc.ac.in
SUMMARY:M.Tech (Res): Direct Numerical Simulation of Turbulent Aerosol Transport in Human Respiratory Flows
DESCRIPTION:Airborne transmission of respiratory diseases is governed by the coupled dynamics of the exhaled turbulent flow and the transport of pathogen-laden aerosols and droplets. This thesis studies two representative respiratory activities\, speech and cough\, and quantifies the infection probability using Direct Numerical Simulations. The incompressible Boussinesq Navier-Stokes equations are solved using Megha-5 solver\, including the required scalar and dispersed-phase transport equations. Speech flow is studied for a repeated plosive-rich utterance at soft\, normal and loud levels. Aerosol exposure is quantified from the instantaneous and time-integrated flux through a face-sized region representing a silent listener at different streamwise separations. Normal and loud speech develop from individual puffs into a jet-like mean flow\, whereas soft speech remains comparatively underdeveloped. The centreline exposure increases in the approximate ratio 1:5.4:18.4\, governed mainly by the source conditions. At a separation of 1 m\, the infection probabilities are approximately 12%\, 28% and 63% for soft\, normal and loud speech\, respectively. For cough flow\, the existing variable-timescale model is compared with a variable-number-density closure based on the Direct Quadrature Method of Moments. The latter transports droplet number density and total surface area as Eulerian fields and captures strong spatial non-uniformity\, particularly within the toroidal vortex at the puff head. It increases the centreline infection probability by 10-30%\, while a laterally displaced breathing zone produces a non-monotonic variation with distance. The results show that infection risk cannot be described by separation distance alone. The framework provides distance-resolved inputs for room-scale and epidemiological transmission models. \n  \nSpeaker : SUBBA REDDY GARI SHASHANK REDDY \nResearch Supervisor : Sourabh Suhas Diwan
URL:https://aero.iisc.ac.in/event/m-tech-res-direct-numerical-simulation-of-turbulent-aerosol-transport-in-human-respiratory-flows/
LOCATION:AE Conference Room \, AE 003
CATEGORIES:Thesis Colloquium / Defence
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/10/SUBBA.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20261009T150000
DTEND;TZID=Asia/Kolkata:20261009T170000
DTSTAMP:20261010T051229
CREATED:20261005T102527Z
LAST-MODIFIED:20261005T102527Z
UID:10000156-1791558000-1791565200@aero.iisc.ac.in
SUMMARY:How important are differential and preferential diffusion effects for hydrogen combustion?
DESCRIPTION:Hydrogen is coming to the forefront as a potential energy carrier to achieve decarbonisation goals and objectives. It is well known that hydrogen is a light molecule diffusing quicker than other molecules and thermal energy in the fuel-air mixture of hydrogen combustion systems. Critical evaluations of these effects have been studied for many decades\, suggesting that they can be ignored while modelling combustion using the RANS approach. However\, recent DNS studies of hydrogen-air turbulent combustion show that these effects ought to be considered.\nTheir importance for practical systems is still an open question\, and finding an unequivocal answer will be the focus of this talk. Specifically\, the aim is to show these effects\, their roles and importance systematically using a priori analysis and a posteriori testing. The findings will highlight the answer\, which is beneficial for numerical modelling and simulations of hydrogen-air partially premixed combustion under practical conditions.\n\nSpeaker: Prof. N. Swaminathan\n\nBiography:\n\nSwaminathan is a professor of mechanical engineering at Cambridge University Engineering Department. His research interests span from candle flames to aero gas turbine combustion and tropical cyclones to bio-acoustics. He explores these multi-scale and multi-physics problems using numerical simulations with the aim to understand the physical mechanisms and to build simple mathematical models for practical use. He has published more than 200 papers and has co-edited two books on turbulent combustion and one on application of machine learning to turbulent combustion. He is a Fellow of Royal Academy of Engineering\, ASME\, IMechE\, Royal Aeronautical Society\, Combustion Institute and Cambridge Philosophical Society.
URL:https://aero.iisc.ac.in/event/how-important-are-differential-and-preferential-diffusion-effects-for-hydrogen-combustion/
LOCATION:Auditorium (AE 005)\, Department of Aerospace Engineering
CATEGORIES:AE Seminar
ATTACH;FMTTYPE=image/jpeg:https://aero.iisc.ac.in/wp-content/uploads/2026/10/9th-Oct-Seminat-.jpg
END:VEVENT
END:VCALENDAR