Next Upcoming Talk:
Ultrashort Pulse Laser Imaging Diagnostics for Combustion, Propulsion, and Plasma ApplicationsDr. Waruna Kulatilaka |
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ABSTRACT Advances in ultrashort-pulse, kHz–MHz-rate laser diagnostics have enabled novel approaches for non-intrusive, multi-dimensional imaging of chemical species in reacting flows. Such diagnostics unravel basic physio-chemical processes in fundamental flames and plasmas, and have applications in practical gas turbine combustors, hypersonic propulsion systems, and energetic material reactions & explosions. The first part of this talk will focus on developing femtosecond (fs) laser-based fluorescence imaging techniques for atoms and molecules in gas-phase reacting flows. In particular, ultrashort, femtosecond laser-induced fluorescence (fs-LIF) methods have enabled interference-free, kHz-rate imaging of highly reactive atomic species such as H, O, and N, molecules such as OH, NO, CO, and O2, and inert tracers such as Kr and Xe in combustion and plasma systems. Several major milestones in the last decade will be highlighted, followed by a discussion on the latest developments in simultaneous multi-species imaging using a single fs laser source. A specific application to carbon-free fuels such as ammonia and hydrogen will be highlighted. The second half of the talk will focus on recent efforts in characterizing the production and evolution of H and O atoms in repetitively pulsed nanosecond plasma discharges using fs two-photon LIF (fs-TPLIF). This study reveals, for the first time, the spatial extent of these reactive radicals and their evolution governed by hydrodynamic processes of consecutive discharges, shedding new light into plasma-assisted combustion in supersonic engines. BIOGRAPHY Dr. Waruna Kulatilaka (Ku. La. Ti. La. Ka) is the Holdredge/Paul Professor in J. Mike Walker ’66 Department of Mechanical Engineering with a joint courtesy appointment in the Department of Aerospace Engineering at Texas A&M University. His research is focused on advanced optical and laser-based diagnostics for fundamental combustion & plasma studies, as well as for a range of applications in propellants & energetics, hypersonics, and ultra-high-rate material impact characterization. His research team was the first to develop femtosecond two-photon laser-induced fluorescence (fs-TPLIF) imaging for highly reactive chemical species such as H, O, and N atoms in flames. Dr. Kulatilaka has also contributed to multiple other laser diagnostic techniques, including LIF, CARS, polarization spectroscopy, and LIBS. His research contributions are reported in nearly 100 peer-reviewed journal articles, over 250 conference papers and presentations, and numerous national and international invited talks. Dr. Kulatilaka serves as the Associate Department Head for Undergraduate Programs in Mechanical Engineering and is active in multiple committees of professional organizations such as ASME, AIAA, and the International Combustion Institute-CI (Chair of the Central States Section of the CI). He is a Fellow of ASME, an Associate Fellow of AIAA, and a Senior Member of Optica. Host: Prof. Ellen Mazumdar |
Previous Talks:
Spin is all you need for mobilityDr. Phanindra Tallapragada |
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ABSTRACT Mobility in robots is usually achieved by a few common means; with a few exceptions these are wheels or legs in ground robots, propellers in flying robots, articulated tails or fins and propellers in swimming robots or flapping flagella in micro swimmers. Nonlinear dynamics can provide insights into alternative means of generating efficient mobility. The talk will present several examples of locomotion produced by the interplay of variations in the inertia tensor, constraints (holonomic and nonholonomic) and periodic actuation. The actuation of such robots is achieved by means of internal actuators that do not directly interact with the environment. Periodic motion or spin of an internal body such as a rotor can transfer high frequency reaction forces and moments that in turn can produce oscillations of flexible structures like tails in a fish-like robot and in legs or cilia in a soft robot. Further these spin-generated forces modulate the forces at surfaces producing discontinuous phenomenon like slipping and jumping. In the low Rynolds number regime, spin actuation can produce propulsion of microswimmers and spinning swimmers can manipulate small particles in a contactless manner. The talk will demonstrate this framework with a spin driven swimming robot which has a locomotion efficiency approaching that of several species of fish, a spin driven pipe crawling robot, a spin driven jumping robot and a spin driven microswimmer and particle manipulator. Spin is all one needs. BIOGRAPHY Phanindra Tallapragada is an associate professor of mechanical engineering at Clemson University. He obtained his Ph.D in Engineering Mechanics from Virginia Tech in 2010 and did post-doctoral research at the University of North Carolina Charlotte. Earlier he obtained his B.Tech and M.Tech in Civil Engineering from the Indian Institute of Technology, Kharagpur. He joined Clemson University as an assistant professor in 2013. His research interests are in dynamical systems and bioinspired locomotion related to terrestrial motion, fish-like swimming, low Reynolds number swimming and operator methods for transport and manipulation in dynamical systems. Host: Prof. Alexander Alexeev |
Hydrodynamic Instabilities in Droplet Breakup at Extreme ConditionsDr. Jacob A. McFarland Recorded Link: Jacob McFarland Fluids Colloquium Seminar-20250116_170603-Meeting Recording.mp4 |
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ABSTRACT Droplet breakup is a complex process involving interfacial instability and transport across a wide range of length and time scales. Fundamental studies of shock-droplet interaction provide valuable insight into the physical processes behind droplet breakup at high Weber and Reynolds numbers. Many high-speed applications such as liquid-fueled detonations and hypersonic hydrometeor impacts involve small droplets under high Weber numbers and unsteady conditions. Kevin-Helmholtz, Rayleigh-Taylor, and other hydrodynamic instabilities evolve through temporally varying conditions to break down the droplet rapidly. Droplet breakup reduces the equilibration time and is closely coupled to evaporation rates. These effects challenge our current computational capabilities, as they require additional models, simulation methods, and experimental validation. The ability to predict these systems, though, is essential to our national defense, and to enhancing our understanding of our universe. This talk will explore the deformation and hydrodynamics leading to breakup for small droplets (< 200 micrometers) at high Weber numbers (>1000). High-speed (>1MHz) shadowgraphy provides measurement of the droplet deformation rate, acceleration, and breakup timing. The deformation rates, acceleration, and breakup times are compared with existing models, and new models for unsteady breakup conditions. BIOGRAPHY Jacob McFarland is an associate professor in the J. Mike Walker Department of Mechanical Engineering at Texas A&M University. He has worked with Lawrence Livermore, and Los Alamos National Laboratories, as well as with the Air Force Research Laboratory and Naval Research Laboratory on shock-driven multiphase flow modeling. He received an NSF CAREER award in 2019 for his work on shock-driven multiphase instabilities and a Young Investigator Award from the ONR in 2020 to study droplet breakup in multiphase detonations. His current research interests are in shock-driven multiphase mixing, droplet breakup, multiphase detonations, and ejecta reaction modeling. Host: Prof. Ellen Yi Chen Mazumdar and Prof. Devesh Ranjan |
EHD of a bubble riseProf. S. Vengadesan |
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ABSTRACT The bubble-rising phenomenon is crucial in diverse industries such as petroleum, pharmaceuticals, polymers, chemical processing, and wastewater treatment. Manipulating bubble behavior, notably through externally applied electric fields, holds significant promise for various applications. The present study focuses on establishing a foundational understanding of bubble rising under the influence of an electric field. To conduct simulations, we developed an in-house electrohydrodynamic solver integrated with an open-source finite volume method (FVM) within the OpenFOAM framework. The solver is meticulously validated against the literature and found to be robust in calculating electrical force and capturing interface in the presence of the electric field. In this talk, I will explain the phenomena of bubble rise due to the effect of electric capillary number (CaE)â , electrical conductivity ratio (R), and permittivity ratio (S). The electrical force comprises dielectrophoretic force (DEF) and Coulomb force, which increases with higher values of CaE, R, and S. As the bubble begins to ascend in the presence of an electric field, the tangential component of the electrical force induces vortices in the vicinity of the bubble, which interact with the bubble’s motion. These interactions result in various phenomena: the ascent of undeformed and deformed bubbles, the ascent of wall-attached bubbles, bubble ascent with path instability, and bubble breakup. In the absence of an electric field, a small spherical bubble exhibits various shapes, including ellipsoidal, ellipsoidal cap, bi-oblate, dimpled ellipsoidal, or retains its original spherical form. BIOGRAPHY Professor Vengadesan has been working with Department of Applied Mechanics and Biomedical Engineering, IIT Madras, Chennai, India for the last 21 years. He specializes in CFD, Multiphase Flow and Unsteady Aerodynamics. He has supervised so far 11 PhD and 31 MS, and currently supervising 9 PhD and 6 MS. He has published 97 journal articles and equal number of conference presentation. Details are available in https://home.iitm.ac.in/vengades/ Host: Prof. Alexander Alexeev |
Dissecting the Causality of Pressure Forces in Vortex Dominated Flows – From Fish Schools to Noisy DronesDr. Rajat Mittal The Johns Hopkins University MRDC 4211 Monday, February 26th 2024 |
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ABSTRACT Pressure-induced drag and lift are key to the performance of wings, rotors and propellers; undulating fins and flapping wings generate forces that are key to locomotion in fish, birds and insects; time-varying fluid dynamic forces drive flutter and flow-induced vibrations of flexible structures in engineering and biology, and these same forces enable the extraction of energy from flow via devices such as wind-turbines. Pressure on a body immersed in a flow is however induced simultaneously by vortices, acceleration reaction (a.k.a. added mass) effects associated with body and/or flow acceleration, and viscous diffusion of momentum, and determining the relative contribution of these different mechanisms on surface pressure remains one of the most important and fundamental issues in fluid dynamics. I will describe the force partitioning method (FPM), a new data-enabled method that partitions pressure forces into components due to vorticity, acceleration reaction and viscous diffusion. FPM has been used to gain new insights into a variety of vortex dominated flows including dynamic stall in pitching foils, vortex-induced vibration of bluff-bodies, hydrodynamics of schooling fish and rough-wall boundary layers, and results from these analyses will be presented. Application of FPM to data generated from experiments will also be described. Finally, FPM has been extended to aeroacoustics, and applications of the aeroacoustic partitioning method (APM) to dissect aeroacoustic noise in engineering and biological flows will be presented. BIOGRAPHY Prof. Rajat Mittal is Professor of Mechanical Engineering at the Johns Hopkins University with a secondary appointment in the School of Medicine. He received the B. Tech. degree from the Indian Institute of Technology at Kanpur in 1989, the M.S degree in Aerospace Engineering from the University of Florida, and the Ph.D. degree in Applied Mechanics from The University of Illinois at Urbana-Champaign, in 1995. His research interests include computational fluid dynamics, vortex dominated flows, biomedical engineering, biological fluid dynamics, fluid-structure interaction, and flow control. He has published over 200 technical articles and multiple patents in these application areas. He is the recipient of the 1996 Francois Frenkiel and the 2022 Stanley Corrsin Awards from the Division of Fluid Dynamics of the American Physical Society, and the 2006 Lewis Moody as well as 2021 Freeman Scholar Awards from the American Society of Mechanical Engineers (ASME). He is a Fellow of ASME and the American Physical Society, and an Associate Fellow of the American Institute of Aeronautics and Astronautics. He is an associate editor of the Journal of Computational Physics, Frontiers of Computational Physiology and Medicine, and serves on the editorial boards of the International Journal for Numerical Methods in Biomedical Engineering, and Physics of Fluids. Host: Prof. Ari Glezer |
Measurement of non-equilibrium in high-speed hydrogen jet flames using spontaneous Raman scatteringDr. Philip Varghese Recorded Link: Fluids Colloquium Seminar_ Dr. Phil Varghese-20221117_170844-Meeting Recording.mp4 |
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ABSTRACT Mixing-induced vibrational non-equilibrium was studied in the turbulent shear layer between a high-speed jet and a surrounding hot-air co-flow. The vibrational and rotational temperatures of N2 and O2 were determined by fitting measured spontaneous Raman scattering spectra to a model that allows for different vibrational and rotational temperatures. The mixing of the jet fluid with the co-flow gases occurs over microsecond time scales, which is sufficiently fast to induce vibrational non-equilibrium in the mixture of hot and cold gases. The effect of fluctuating temperatures on the time-averaged Raman measurement was quantified using single-shot Rayleigh thermometry. The Raman scattering results were found to be insensitive to fluctuations except where the flame is present intermittently. Vibrational non-equilibrium was detected in nitrogen but not in oxygen. This difference between species temperatures violates the two-temperature assumption often used in the modeling of high-temperature non-equilibrium flow. A multiple-pass cell was constructed to obtain single-shot Raman scattering measurements in the turbulent shear layer using a pulsed stretched laser. These measurements agreed with the previous time-average results and allowed us to make measurements near the fluctuating base of a lifted flame – a region where time-averaged measurements do not give meaningful results. BIOGRAPHY Prof. Varghese holds the Ernest H. Cockrell Centennial Chair in Engineering and is the Director of the Center for Aeromechanics Research at UT Austin. His research focuses on understanding the basic molecular processes occurring in high speed and high temperature, and non-equilibrium flows. This is an inter-disciplinary field, requiring a synthesis of physics and chemistry with the more traditional engineering disciplines of fluid mechanics, heat transfer, and thermodynamics. He applies his work to the study of hypersonic and rarefied flows, plasmas, and combustion. He was a Fulbright Senior Scholar in France in 1993. He received the Lockheed Martin Aeronautics Company Award for Excellence in Engineering Teaching in Spring 2003, and was elected to the Academy of Distinguished Teachers at the University of Texas in 2005. In February 2012 he was selected Professor of the Year by the Senate of College Councils and was awarded The University of Texas System Regents’ Outstanding Teaching Award in August 2016. Host: Prof. Ellen Yi Chen Mazumdar |
Sandia National Laboratories Autonomy for HypersonicsDr. Hartono (Anton) Sumali |
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ABSTRACT Sandia National Laboratories is a Federally Funded, Research and Development Center (FFRDC). Through the Autonomy for Hypersonics (A4H) Mission Campaign, Sandia National Laboratories is investing internal funds to explore autonomous systems technologies to increase the warfighting utility of hypersonic weapon systems. A4H is a 6.5 year-long strategic initiative that will enable rapid mission planning for response to time-sensitive threats and develop technologies for highly adaptive vehicles that intelligently sense their environment, determine a course of action in real time, and then robustly navigate, guide, and control to intended targets. Autonomous systems are typically characterized using the “SENSE-THINK-ACT” loop for enabling for autonomous operations. While today’s hypersonic flight systems are already autonomous, their operational relevance is significantly limited by their current abilities to perceive and adapt to their environment. A4H is working to enhance the SENSE-THINK-ACT loop to facilitate onboard intelligence, perception, and reasoning in hypersonic systems. Research within the A4H portfolio has already begun to transition from proof-of-concept demonstrations to higher-level tech maturation. As the A4H team enters the second half of the Mission Campaign, we have successfully transitioned research projects to customer-funded test flights including an autonomous mission planning solution and robust, optimized vehicle control algorithms. This presentation provides a general overview of Sandia National Laboratories, and more specifically a vision for the future of autonomous hypersonics as well as how A4H is advancing key capabilities in support of this vision. The presentation will spotlight projects from the portfolio as well as highlight efforts for risk reduction and tech transition of next-generation algorithms, techniques, and tools to Sandia’s hypersonic mission space. BIOGRAPHY Dr. Hartono (Anton) Sumali manages the Autonomous Sensing And Controls Department at Sandia National Laboratories in Albuquerque, New Mexico, USA. He received his PhD in Mechanical Engineering in 1997 from Virginia Polytechnic Institute and State University in Blacksburg, Virginia, USA. From 1997 to 2002 he was an Assistant Professor at Purdue University in West Lafayette, Indiana, USA. He has authored or co-authored over 100 technical publications, mostly in MEMS and structural dynamics. Host: Prof. Ellen Yi Chen Mazumdar |
Laser Diagnostic Applications in Hypersonic Ground-Test Facilities at SandiaDr. Sean P. Kearney Live MS Teams Link: https://tinyurl.com/56dc4rjn |
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ABSTRACT BIOGRAPHY Host: Prof. Ellen Yi Chen Mazumdar |
Laser Diagnostics in Propulsion and PowerTalk Hosted by the Georgia Tech School of Mechanical Engineering Dr. Adam Steinberg Live MS Teams Link: https://tinyurl.com/4mev3wjr |
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ABSTRACT BIOGRAPHY Host: Prof. Ellen Yi Chen Mazumdar |
Turbulence and Reduced Models for Large Wind FarmsDr. Charles Meneveau Live Link: https://primetime.bluejeans.com/a2m/live-event/qjqevqfz |
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ABSTRACT BIOGRAPHY Charles Meneveau is the Louis M. Sardella Professor in the Department of Mechanical Engineering, is Associate Director of the Institute for Data Intensive Engineering and Science (IDIES) and is jointly appointed as Professor in the Department of Physics and Astronomy at Johns Hopkins. He received his B.S. degree in Mechanical Engineering from the Universidad Técnica Federico Santa María in Valparaíso, Chile, in 1985 and M.S, M.Phil. and Ph.D. degrees from Yale University in 1987, 1988 and 1989, respectively. During 1989/90 he was a postdoctoral fellow at the Center for Turbulence Research at Stanford. He has been on the Johns Hopkins faculty since 1990. His area of research is focused on understanding and modeling hydrodynamic turbulence, and complexity in fluid mechanics in general. The insights that have emerged from Professor Meneveau’s work have led to new numerical models for Large Eddy Simulations (LES) and applications in engineering and environmental flows, including wind farms. He also focuses on developing methods to share the very large data sets that arise in computational fluid dynamics. He is Deputy Editor of the Journal of Fluid Mechanics and has served as the Editor-in-Chief of the Journal of Turbulence. Professor Meneveau is a member of the US National Academy of Engineering, a foreign corresponding member of the Chilean Academy of Sciences, a Fellow of APS, ASME, AMS and recipient of the Stanley Corrsin Award from the APS, the JHU Alumni Association’s Excellence in Teaching Award, and the APS’ François N. Frenkiel Award for Fluid Mechanics. Host: Prof. Ellen Yi Chen Mazumdar |
Heat and Mass Transfer Resulting in Eruptive Jetting from Stems and Leaves during Distillation Stage of Forest FireDr. Alexander L. Yarin Live Link: https://primetime.bluejeans.com/a2m/live-event/zzajkggj |
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![]() ABSTRACT BIOGRAPHY Host: Prof. Ellen Yi Chen Mazumdar |
Flowing and clogging of soft particles and dropletsDr. Eric Weeks Live Link: https://primetime.bluejeans.com/a2m/live-event/hybwaajz |
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ABSTRACT BIOGRAPHY Host: Prof. Ellen Yi Chen Mazumdar |
Natural and machine olfaction and cube-shaped pooDr. David L. Hu |
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Live Link: https://primetime.bluejeans.com/a2m/live-event/zbceuvkp ABSTRACT BIOGRAPHY Host: Prof. Ellen Yi Chen Mazumdar |