Conferences, Lectures, & Seminars
Events for November
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Aerospace & Mechanical Engineering Seminar
Wed, Nov 01, 2017 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: Antonino Ferrante, Associate Professor, University of Washington
Talk Title: On the Physical Mechanisms of Droplet/Turbulence Interaction
Abstract: The interactions of liquid droplets with turbulence are relevant to both environmental flows and engineering applications, e.g., rain formation and spray combustion. The physical mechanisms of droplet-turbulence interaction are largely unknown. The main goal of this research is to investigate the physical mechanisms of droplet-turbulence interaction for both non-evaporating and evaporating droplets.
Droplets in turbulent flows behave differently from solid particles, e.g., droplets deform, break up, coalesce and have internal fluid circulation. We have developed a new pressure-correction method for simulating incompressible two-fluid flows with large density and viscosity ratios. The method's main advantage is that, for example, on a 10243 mesh, our new pressure--correction method using the FFT-based parallel Poisson solver is forty times faster than the standard method using multigrid. In general, the new pressure-correction method could be coupled with other interface advection methods such as level-set, phase-field, or front-tracking. We have coupled the pressure-correction method with a volume-of-fluid method for its properties of being mass conserving and sharp-capturing of the interface.
We performed direct numerical simulation (DNS) of finite-size, non-evaporating droplets of diameter approximately equal to the Taylor lengthscale in decaying isotropic turbulence. We studied the effects of Weber number, viscosity ratio and density ratio. We derived the turbulence kinetic energy (TKE) equations for the two-fluid, carrier-fluid and droplet-fluid flow. This allows us to explain the pathways for TKE exchange between the carrier turbulent flow and the flow inside the droplet. The role of the interfacial surface energy is explained through the power of surface tension term of the two-fluid TKE equation. Also, we derive the relationship between the power of surface tension and the rate of change of total droplet surface area. This allows us to explain how droplet deformation, breakup and coalescence plays a role on the temporal evolution of TKE. Our DNS results show that increasing Weber number, the droplet to fluid density or viscosity ratios increases the decay rate of the two-fluid TKE relative to that of single-phase flow. Via analysis of the DNS results, the revealed physical mechanisms will be presented.
Recently, we have also extended the volume-of-fluid method to simulate evaporating droplets. The verification and validation of the method and the DNS results will be presented in comparison to theory and experiments.
Biography: Antonino Ferrante is an Associate Professor of the William E. Boeing Department of Aeronautics & Astronautics at the University of Washington (UW). In 2004, he received the Ph.D. in Mechanical and Aerospace Engineering from the University of California, Irvine, where he continued his research as Postdoctoral Scholar until 2007. From 2007 to 2009, he was Postdoctoral Scholar in Aeronautics at the California Institute of Technology at GALCIT. In 2009, he joined the UW as Assistant Professor where was tenured in 2015. Ferrante is recipient of the NSF CAREER Award (2011). His research is focused to the understanding of the physical mechanisms of complex flows, e.g. multiphase and wall-bounded turbulent flows, and enable that through the development of parallel computational methodologies for simulating such flows on supercomputers.
Host: Department of Aerospace and Mechanical Engineering
Location: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: Ashleen Knutsen
This event is open to all eligible individuals. USC Viterbi operates all of its activities consistent with the University's Notice of Non-Discrimination. Eligibility is not determined based on race, sex, ethnicity, sexual orientation, or any other prohibited factor. -
Aerospace & Mechanical Engineering Seminar
Wed, Nov 08, 2017 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: James J. Riley, PACCAR Professor of Engineering, University of Washington
Talk Title: The Effects of Stable Density Stratification Initially Homogeneous, Isotropic Turbulence
Abstract: Stable density stratification occurs in various situations in the atmosphere and in the oceans. For example, in the atmosphere stable density stratification is found near the tropopause and above, and often in nocturnal boundary layers, while in the oceans it usually is observed below the mixed layer. And, through its effects on turbulent mixing, stable stratification has relevance to a number of important issues such as the overall ocean thermal energy balance and the transfer rates of heat and chemicals to/from the atmosphere.
In this seminar the results are presented of a study of the effects of stable density stratification on the simplest of turbulent flows, initially homogeneous, isotropic turbulence, using direct numerical simulations. Simulations were carried out at an initially moderate Froude number, but for a range of initial Reynolds numbers such that, for the high Reynolds number cases, the flows had buoyancy Reynolds numbers in the hundreds, similar to typical oceanic values. A number of aspects of the flows have been addressed, including their energetics, the behavior of various velocity and length scales describing the flows, their mixing characteristics, and their spectral behavior. In particular, how the behavior of the flows depend on the local Froude and buoyancy Reynolds numbers is emphasized. It is found, for example, that as the flows decay, stratification modifies them such that, compared to non-stratified cases, the energy decay rates decreased, the growth rate of the horizontal scales increased, while the growth rates of the vertical scales became negative. These results are consistent with the analysis of Davidson (J. Fluid Mech., 2010), based upon the behavior of the effects of density stratification on the large-scale motions. On the other hand if the buoyancy Reynolds number becomes too low, then the flows, especially the vertical velocity, begin to decay much more rapidly. It is also found, for example, that the behavior of the spectra of the velocity gradient tensor is consistent with the heuristic arguments of Lilly (J. Atmos. Sci., 1983) and the scaling arguments of Billant & Chomaz (Phys. Fluids, 2001). Finally, previous results of the USC group (e.g., Spedding J. Fluid Mech., 1997) are interpreted in terms of the Froude and buoyancy Reynolds numbers.
Biography: James J. Riley is the PACCAR Professor of Engineering at the University of Washington. He received his PhD from the Johns Hopkins University in 1972, having worked under the guidance of Stanley Corrsin. After a year as a post-doctoral fellow at the National Center for Atmospheric Research, he spent ten years in industry at Flow Research Company in Kent, Washington, ultimately as the Director of the Fluid Mechanics Division. He joined the University of Washington in 1983, where he is now a Professor in the Department of Mechanical Engineering, and an Adjunct Professor in both the Departments of Applied Mathematics and of Aeronautics and Astronautics. While on sabbatical at the Joseph Fourier University in Grenoble, France, Riley occupied the Visiting Chair in Industrial Mathematics. More recently he was a Senior Fellow at the Isaac Newton Institute for the Mathematical Sciences at Cambridge University. Riley's research interests have included particle dispersion in turbulent flows, waves and turbulence in stably-stratified and in rotating fluids, boundary layer and shear layer transition and turbulence, fluid/compliant surface interactions, and chemically reacting turbulent flows. He is an associate editor of the Journal of Fluid Mechanics and of the Journal of Turbulence, and until recently was a member of the editorial boards of the Annual Review of Fluid Mechanics and of the Applied Mechanics Reviews. Riley is a member of the National Academy of Engineering, and of the Washington State Academy of Sciences.
Host: Department of Aerospace and Mechanical Engineering
Location: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: Ashleen Knutsen
This event is open to all eligible individuals. USC Viterbi operates all of its activities consistent with the University's Notice of Non-Discrimination. Eligibility is not determined based on race, sex, ethnicity, sexual orientation, or any other prohibited factor. -
Aerospace & Mechanical Engineering Seminar
Wed, Nov 15, 2017 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Speaker: Tim Lieuwen, Professor, Georgia Institute of Technology
Talk Title: Unsteady Combustion Problems in Modern Energy and Propulsion Systems
Abstract: The operational limits of modern power generation and propulsion devices are strongly influenced by the combustor. For example, combustion instabilities have emerged as one of the leading challenges associated with low emissions combustion technologies. More fundamentally, the combustion instability problem involves the nonlinear interactions of harmonic flow disturbances with flames in a highly turbulent flow. This talk will describe the key processes controlling the flame response - flame anchoring, excitation of wrinkles by flow oscillations, tangential convection of wrinkles upon the flame, and kinematic restoration.
Biography: Tim Lieuwen is a professor and the David S. Lewis, Jr. Chair at Georgia Institute of Technology, and the Executive Director of the Strategic Energy Institute. He has a Ph.D. in mechanical engineering and is a licensed professional engineer in the state of Georgia. He leads a diverse research group investigating a range of problems associated with clean power, energy, and combustion, including such issues as emissions, efficiency, and alternative fuels. Prof. Lieuwen has edited/written four books, written 7 book chapters and over 300 papers, and received 5 patents.
Host: Department of Aerospace and Mechanical Engineering
Location: Seaver Science Library (SSL) - 150
Audiences: Everyone Is Invited
Contact: Ashleen Knutsen
This event is open to all eligible individuals. USC Viterbi operates all of its activities consistent with the University's Notice of Non-Discrimination. Eligibility is not determined based on race, sex, ethnicity, sexual orientation, or any other prohibited factor.
