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)⁠, 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 Alexev

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

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

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

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

ABSTRACT
Hypersonic flight systems are seeing significant renewed interest in recent years. The problem space presents a rich combination of physics, where compressible fluid mechanics is coupled with non-equilibrium thermochemistry at high, MJ/kg flight enthalpies. Sandia supports hypersonic system development with mod-sim and ground-test capabilities that are supported by co-located expertise in high-fidelity laser diagnostics. The focus of this talk is recent development of laser-diagnostic platforms for applications in hypersonic ground testing. In the bulk of the presentation, we will discuss coherent anti-Stokes Raman scattering (CARS) applications to multiple ground-test facilities.  A wide variety of laser platforms featuring femtosecond- to nanosecond-duration laser pulses are used depending on ground-test requirements. Nanosecond laser pulses are applied to access extreme temperatures (T = 5000-7000 K) for materials testing efforts in an inductively coupled air plasma torch. Simultaneous temperature/pressure measurements in low-temperature (50-290 K) jets and Mach-8 wind-tunnel flows are demonstrated using ultrashort-pulse femtosecond CARS for hybrid time-/frequency-domain detection. Picosecond N₂ CARS thermometry at 100-kHz rates using a pulse-burst laser architecture is demonstrated Sandia’s free-piston-driven shock tube, where temperatures readily exceed 4000 K. The talk concludes with a summary of additional laser-diagnostic measurements in Sandia facilities, including nitric-oxide detection using pulse-burst laser-induced fluorescence and high-speed absorption spectroscopy in high-enthalpy flows, and new rapid-scanning concepts for Doppler global velocimetry applied to Sandia’s hypersonic wind tunnel.

BIOGRAPHY
Sean Kearney is a Distinguished Member of the Technical Staff in Sandia’s Engineering Sciences Center, where he has worked since 1999 to develop and apply laser-based diagnostics to a wide variety of national-security mission areas, including as nuclear safety, combustion, hypersonics, microsystems, and energetic materials. His current research interests are focused on burst-mode and ultrashort-pulse laser diagnostics applied to hypersonics, pyrotechnics, and explosive devices. He holds a Bachelor of Science degree in Mechanical Engineering from Clarkson University and Mechanical Engineering M.S. and Ph.D. degrees from the University of Illinois at Urbana-Champaign. Sean is active in the Optical Society of America (OSA) and is an Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA), where he serves as incoming chair of AIAA’s Aerodynamic Measurement Technology (AMT) Technical Committee. 

Host: Prof. Ellen Yi Chen Mazumdar

ABSTRACT
Laser-based measurement techniques help reveal the inner workings of complicated physical systems – such as aerospace propulsion and power generation engines – allowing us to better understand, predict, and engineer their behavior. After a brief overview of some relevant laser diagnostics and their applications, this talk will delve into two recent developments in greater detail. Firstly, we will discuss the use of terahertz time domain spectroscopy (THz-TDS) for making measurements inside of Hall thrusters, which are an important propulsion technology for future long-distance space missions. We present a novel Bayesian framework for simultaneously deducing the electron number density and collision frequency, and demonstrate its use in plasmas bounded by Hall thruster wall material. These measurements open the possibility for explaining key physics affecting Hall thruster performance and durability. Secondly, we will discuss the use of tomographic particle image velocimetry (TPIV) and formaldehyde planar laser induced fluorescence (PLIF) to investigate flame-scale turbulence production and cross-scale kinetic energy transfer in a model gas turbine swirl combustor. We provide the first experimental measurement of mean up-scale kinetic energy transfer (back-scatter) within the flame, which is counter to the forward cascade hypothesis underpinning popular (purely dissipative) turbulence closure models.

BIOGRAPHY
Adam Steinberg is an Associate Professor in the School of Aerospace Engineering at Georgia Tech and the Director of the Ben T. Zinn Combustion Lab. Prior to joining Tech, he held a Canada Research Chair as an Associate Professor at the University of Toronto Institute for Aerospace Studies and served as a Research Associate at the German Aerospace Center. His research focuses on overcoming the scientific and technical barriers facing future aerospace propulsion and energy conversion devices. Working closely with government and industry, his research group develops and applies advanced laser-based measurement techniques that help unravel the coupled thermal, fluid, and chemical process occurring in these devices. Topics of interest include light/matter interactions, turbulence, combustion, gas turbine engines, chemical rockets, electric space propulsion, high-speed flows, data analysis, and experiment/simulation coupling. Dr. Steinberg is an Associate Fellow of the AIAA and Associate Editor of Combustion and Flame.

Host: Prof. Ellen Yi Chen Mazumdar

ABSTRACT
In this presentation we discuss several properties of the flow structure and turbulence in the wind turbine array boundary layer (WTABL). This particular type of shear flow develops when the atmospheric boundary layer interacts with an array of large wind turbines. Based on such understanding, we aim to develop reduced order, analytically tractable models. These are important engineering tools for wind energy, both for design and control purposes. After reviewing some basic tools to predict mean velocities for total power optimization, we will focus on some fluid mechanical themes relevant to wind farm control and inherent variability. We describe a simple (deterministic) dynamic wake model, its use for wind farm control, and its extensions to the case of yawed wind turbines based on a re-interpretation of lifting line theory adapted to the problem of yawed actuator disks. Time permitting, we also discuss spectral characteristics of the fluctuations in power generated by an array of wind turbines in a wind farm. We show that modeling of the spatio-temporal structure of canonical turbulent boundary layers coupled with variants of the Kraichnan’s random sweeping hypothesis can be used to develop analytical predictions of the frequency spectrum of power fluctuations of wind farms. The work to be presented arose from collaborations with Richard Stevens, Marc Calaf, Johan Meyers, Carl Shapiro, Dennice Gayme, Gen Starke, Juliaan Bossuyt, Michael Howland and Michael Wilczek. We are grateful for National Science Foundation financial support.

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

ABSTRACT
Forest fires are common large-scale environmental disasters with annual death toll and damages on the scale of tens of billions of dollars. We explore experimentally and theoretically a novel mechanism responsible for fuel and water vapor supply into flame in the form of volatiles-water vapor jets erupting from plants engulfed in fire. This mechanism is significantly accelerated in comparison with the ordinary-implied evaporation/sublimation and diffusion characteristic of the diffusion flames. The eruptive jets accelerate fuel supply into the flame zone and plant drying before burning, which facilitates forest fire. They also ballast the flame zone with water vapor, i.e. provide a counter-acting flame-quenching path. The eruptive jets are observed in the experiments with horizontal stems and leaves subjected to the engulfing flame, and the results are explained and predicted theoretically. Also, as a model system, a horizontal syringe needle filled with liquids and subjected to the surrounding flame is used as a stem substitute to separate the effect of water vapor from that of combustible volatiles modeled by ethanol. The predicted eruption velocity of ~10 m/s is in good agreement with the experimental data.

BIOGRAPHY
MSc-1977 (in Applied Physics), PhD (in Physics and Mathematics)-1980, DSc (Habilitation, (in Physics and Mathematics)-1989. Affiliations: The Institute for Problems in Mechanics of the Academy of Sciences of the USSR, Moscow (1977-1990); Professor at The Technion-Israel Institute of Technology (1990-2006; Eduard Pestel Chair Professor in Mechanical Engineering at The Technion in 1999-2006); Distinguished Professor at The University of Illinois at Chicago, USA (2006-present); Fellow of the American Physical Society. Prof. Yarin is the author of 5 books, 12 book chapters, 400 research papers, and 12 patents. Prof. Yarin was the Fellow of the Rashi Foundation, The Israel Academy of Sciences and Humanities, and was awarded The Gutwirth Award, The Hershel Rich Prize, and The Prize for Technological Development for Defense against Terror of the American-Technion Society. He is one of the three co-Editors of ‘Springer Handbook of Experimental Fluid Mechanics’, 2007, the Associate Editor of the journal “Experiments in Fluids”, and the member of the Editorial Advisory Board of ‘Physics of Fluids’, the Bulletin of the Polish Academy of Sciences, and ‘Archives of Mechanics’.

Host: Prof. Ellen Yi Chen Mazumdar

ABSTRACT
We study the flow and clogging of generally soft particles: micron-sized oil droplets, centimeter-sized hydrogel particles, and simulated soft particles.  We find that softness is a key factor controlling clogging:  with stiffer particles or a weaker driving force, clogging is easier.  Softer particles form less stable arches and thus reduce the probability of clogging.  Our results suggest that prior studies using hard particles were in a limit where the role of softness is negligible, which causes clogging to occur with significantly larger openings.  We also examine a complementary situation, where flow of oil droplets is driven by constant flux rather than constant force, and find intermittent clogging and avalanches.

BIOGRAPHY
Eric Weeks earned his undergraduate degree in engineering physics at the University of Illinois at Urbana-Champaign. (“Engineering” physics meant he had to take drafting and Fortran.)  In 1997 he graduated with a Ph.D. in physics from the University of Texas at Austin, working in the Center for Nonlinear Dynamics with Prof. Harry Swinney.  His dissertation was on experiments studying anomalous diffusion and atmospheric phenomena.  He started a postdoctoral fellowship at the University of Pennsylvania with Prof. David Weitz and Prof. Arjun Yodh, and finished his postdoctoral work at Harvard University when the Weitz lab moved there.  In January 2001 he joined the faculty of Emory University, where he is currently a Dobbs Professor of Physics.  Since July 2018 he has also been the Director of Emory’s Center for Faculty Development and Excellence.

Host: Prof. Ellen Yi Chen Mazumdar

Live Link: https://primetime.bluejeans.com/a2m/live-event/zbceuvkp
Recorded Talk: https://primetime.bluejeans.com/a2m/events/playback/9e0a45e9-b36a-4915-b9fc-f39b3a7762d9

ABSTRACT
The need to escape predators, find mates, and detect prey has pushed the envelope for speed and sensitivity in odor detection. Understanding how animals achieve their sensitive sense of smell can lead to better electronic noses. In this talk, we present the fluid mechanics underlying the olfactory abilities of moths and mammals, spanning eight orders of magnitude in body mass. Male moths can detect female moths from over 6 km away, and dogs have a lower detection limit of one part per trillion, which is three orders of magnitude more sensitive than today’s instruments. We mimic the deposition of odor particles using laboratory wind tunnels that generate both steady-state and periodic flow to mimic sniffing. Critical to both processes is slowing the airflow to encourage diffusion to the sensors. In the remaining time, I will talk about my experiences winning an Ig Nobel Prize at Harvard University for showing how wombats make cube-shaped poo.

BIOGRAPHY
Dr. David Hu is a mechanical engineer who studies animal movement. Originally from Rockville, Maryland, he earned degrees in mathematics and mechanical engineering from M.I.T., and is now Professor of Mechanical Engineering and Biology and Adjunct Professor of Physics at Georgia Tech. He is a recipient of the National Science Foundation CAREER award for young scientists, two Ig Nobel Prizes in Physics, three Pineapple Science Prizes (the Ig Nobel of China), the American Institute of Physics Science Communication Award, and others. His work been featured in The Economist, The New York Times, Saturday Night Live, Highlights for Children, and he has been an invited guest on Good Morning America, Discovery Channel, National Public Radio. He is the author of the book “How to Walk on Water and Climb up walls,” published by Princeton University Press, and a 2020 Finalist for the AAAS/Subaru Prize for Excellence in Young Adult Science Books.
https://www.nytimes.com/2018/11/05/science/hu-robotics.html

Host: Prof. Ellen Yi Chen Mazumdar

ABSTRACT
Within the last decade, high-speed digital camera technologies have steadily improved and their use in science and engineering has become ubiquitous. Yet, extracting quantitative measurements from video results remains challenging for many applications. This presentation will focus on development of new diagnostics to address many of the extreme imaging challenges at Sandia National Laboratories. To recover the missing third-dimension, we will discuss the development and application of digital in-line holography (DIH), plenoptic imaging, and multi-camera triangulation. To minimize image degradation due to thermal gradients and shock-waves, we will discuss phase-conjugate and x-ray diagnostics. Finally, to maximize information when optical access is limited, optical time of flight sectioning will be presented. These diagnostics will be demonstrated for a range of applications from liquid sprays, combustion, and energetics at imaging speeds up to millions of frames per second.

BIOGRAPHY
Daniel R. Guildenbecher is a Principle Member of the Technical Staff at Sandia National Laboratories in Albuquerque, New Mexico. Dr. Guildenbecher’s research emphasizes experimental diagnostics of multiphase flows, particularly those involving particle transport, liquid fragmentation, combustion, and energy conversions. Dr. Guildenbecher received his Ph.D. in Mechanical Engineering from Purdue University in 2009. Prior to joining Sandia, Dr. Guildenbecher was a Visiting Professor at the Karlsruhe Institute of Technology (2009-2010) and Purdue University (2010-2011).

Host: Prof. Ellen Yi Chen Mazumdar