MechSE Seminars
http://illinois.edu/calendar/list/2791
Department of Mechanical Science and EngineeringLow Reynolds number flows through shaped and deformable conduits
http://illinois.edu/calendar/detail/2791/32318760
MechSE Seminarhttp://illinois.edu/calendar/detail/2791/32318760Thu, 29 Jan 2015 12:00:00 CSTAbstract:Unconventional fossil energy resources are revolutionizing the US energy market. While the techniques developed over the last 50 years lead to viable and profitable extraction of, e.g., trapped gas and hydrocarbons from almost impermeable rock formations via hydraulic fracturing, the abysmal extraction rates (typically 15%) suggest the fluid mechanics of these processes is not well understood. In this talk, I will describe three basic theoretical fluid mechanics problems inspired by unconventional fossil fuel extraction. The first problem is flow in a deformable microchannel. Fluid-structure interaction couples the shape of the conduit to the flow through it, drastically altering the flow rate, pressure drop relation. Using perturbation methods, we show that the flow rate is a quartic polynomial of pressure drop for shallow channels, in contrast to the linear relation for rigid conduits. The second problem involves two-phase (gas-liquid) displacement in a horizontal Hele-Shaw cell with an elastic membrane as the top boundary. This problem arises at the pore-scale in enhanced oil recovery for large injection pressures. Once again, fluid-structure interaction alters the problem, leading to stabilization of the Saffman-Taylor (viscous fingering) instability below a critical flow rate. Using lubrication theory, we derive the stability threshold and show that it agrees well with recent experiments. The third problem involves the spread of a viscous liquid in a vertical Hele-Shaw cell with a variable thickness in the flow-wise direction, as a model for the spread of a plume of supercritical carbon dioxide through the non-uniform passages created by hydraulic fracturing. We show that the propagation regimes in such a shaped conduit are set by the direction of propagation. While the rate of spread in the direction of increasing gap thickness (and, hence, permeability) can be obtained by standard scaling techniques, the reverse scenario requires the construction of a so-called second-kind, self-similar solution, leading to nontrivial exponents in the rate of spread.About the Speaker:Ivan Christov received his Ph.D. in Engineering Sciences and Applied Mathematics from Northwestern University. Subsequently, he was awarded an NSF Mathematical Sciences Postdoctoral Research Fellowship and spent two years with the Complex Fluids Group at Princeton University. Currently, he is the Richard P. Feynman Distinguished Postdoctoral Fellow in Theory and Computing at the Center for Nonlinear Studies at Los Alamos National Laboratory. He regularly participates in international collaborative research (most recently at the Oxford Centre for Collaborative Applied Mathematics). Previously, he has worked at the U.S. Naval Research Laboratory and the ExxonMobil Upstream Research Company. His research interests are primarily in the area of modeling and numerical simulation of transport phenomena with an emphasis on complex and nonlinear systems and an outlook towards problems arising in next-generation energy resource utilization.Host: Sascha HilgenfeldtTurbulence in wind farm boundary layers
http://illinois.edu/calendar/detail/2791/32313293
MechSE Departmental Seminarhttp://illinois.edu/calendar/detail/2791/32313293Tue, 28 Apr 2015 15:00:00 CDTAbstractSimilar to other renewable energy sources, wind energy is characterized by low power density. Hence, in order for wind energy to make a significant contribution to our overall energy supply, large wind farms (on or off-shore) need to be envisioned. As it turns out, not much is known about the interactions between large wind farms and the atmospheric boundary layer. A case in point, as wind farms are getting larger, operators have begun to complain about the so-called "wind-farm underperformance" problem. This presentation will summarize our results that focus on understanding how wind turbines, when deployed in large arrays, extract kinetic energy from the atmospheric boundary layer. Large Eddy Simulations (LES) are used to improve our understanding of the vertical transport of momentum and kinetic energy across a boundary layer flow with wind turbines. A suite of LES, in which wind turbines are modeled using the classical `actuator disk' concept, are performed for various wind turbine arrangements, turbine loading factors, and surface roughness values. The results are used to develop improved models for effective roughness length scales and to obtain new optimal spacing distances among wind turbines in a large wind farm. We introduce the notion of generalized transport tubes as a new tool for flow visualization that is particularly useful to analyze the spatial transport of particular physical quantities (e.g. kinetic energy arriving at a particular wind turbine). Finally, we introduce a new engineering model, the Coupled Wake Boundary Layer model that reconciles wake expansion/superposition models currently used in industry with the vertical structure of the atmospheric boundary layer. This work is a collaboration with colleagues, postdocs and students involved in the WINDINSPIRE project and is supported by the US National Science Foundation.About the SpeakerCharles Meneveau is the Louis M. Sardella Professor in the Department of Mechanical Engineering at Johns Hopkins University. He serves as deputy director of the Institute for Data Intensive Engineering and Science (IDIES) at Johns Hopkins, as Deputy Editor of the Journal of Fluid Mechanics, and as the Editor-in-Chief of the Journal of Turbulence. 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 Stanford University/NASA Ames' Center for Turbulence Research. Professor Meneveau 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. He combines experimental, computational, and theoretical tools for his research. At present, he is interested in fluid dynamics of large wind farms, public databases, and subgrid and wall modeling for Large Eddy Simulations and various applications of LES. With his students and co-workers, he has authored over 200 peer-reviewed articles. Professor Meneveau is a foreign corresponding member of the Chilean Academy of Sciences, and a Fellow of the American Academy of Mechanics, the U.S. American Physical Society and the American Society of Mechanical Engineers. He received the inaugural Stanley Corrsin Award from the American Physical Society (2011), the 2011 J. Cole Award from AIAA, the 2004 UCAR Outstanding Publication award (with students and other colleagues at JHU and NCAR), the Johns Hopkins University Alumni Association's Excellence in Teaching Award (2003), and the APS' François N. Frenkiel Award for Fluid Mechanics (2001). In the past, he has served as member of the Editorial Committee of the Annual Reviews of Fluid Mechanics and as an Associate Editor for Physics of Fluids.Host: Professor Jonathan Freund