IACS seminars are free and open to the public; no registration required. Lunch will not be provided.
ABSTRACT: Wall-bounded turbulence has been of great concern at least since it's description as a fluid dynamic phenomenon by Osborne Reynolds in 1883. The reason, of course, is that in such turbulent wall-bounded flows, the turbulence is responsible for transport of momentum and heat from the bulk flow to the wall. It has long been recognized that wall-bounded shear flows at high Reynolds number are characterized by a thin viscous dominated inner layer at the wall and a thick inertially dominated outer layer away from the wall, with a matching region in between known as the log layer. However, the dynamics of the interaction between the inner and outer layers is not well understood. In this talk, Dr. Moser will address this shortcoming using data from direct numerical simulations (DNS) of turbulent channel flow.
Several years ago, Dr. Moser’s research team completed a DNS of a channel flow at high enough Reynolds number for it to exhibit a significant separation of scales between the inner and outer layer turbulence. This high Reynolds number simulation allows, for the first time, the investigation of the the interaction between inner and outer layers using DNS. The data from this simulation has been used to evaluate the spectrum (in horizontal directions) of the terms in the evolution equation for the Reynolds stress. This data has revealed several remarkable features of wall-bounded turbulence in the log layer and of the interaction between inner and outer layer turbulence. In particular, it is found that turbulence production in the log and outer layers dominantly occurs in modes that are extremely elongated in the streamwise direction with spanwise length scales greater than 1000 wall units. The generation of energy in these large-scale elongated modes results in an intricate set of energy exchanges, including transport from the outer layer into the inner layer in these same large scale elongated modes, resulting in modulation of the near-wall autonomous dynamics of the inner layer. This and other features of the wall turbulence dynamics will be discussed, as will their implications for large eddy simulation.
Research by Robert D. Moser and Myoungkyu Lee, Postdoctoral Researcher in the Sandia National Laboratories, Livermore.
BIO: Robert D. Moser holds the W. A. "Tex" Moncrief Jr. Chair in Computational Engineering and Sciences and is a professor of Mechanical Engineering in thermal fluid systems at the University of Texas. He serves as the Director of the Center for Predictive Engineering and Computational Sciences (PECOS) and Deputy Director of the Institute for Computational Engineering and Sciences (ICES). Moser received his PhD in mechanical engineering from Stanford University. Before coming to the University of Texas, he was a research scientist at the NASA-Ames Research Center and then a professor of Theoretical and Applied Mechanics at the University of Illinois. Moser conducts research on the modeling and numerical simulation of turbulence and other complex fluid flow phenomena. He also uses direct numerical simulation to investigate and model turbulent flows, particularly the development and evaluation of large eddy simulation models. Moser has been working to develop new approaches for the validation of and quantification of uncertainty in computational models and to assess their reliability. He has pursued applications to such diverse systems as reentry vehicles, solid propellant rockets, micro-air vehicles, turbulent combustion, tokamak fusion and energy harvesting. He is a Fellow of the American Physical Society, and was awarded the NASA Medal for Exceptional Scientific Achievement.