Weekly Seminar: Fall 2014
Speaker: Prof. Lakshmi P. Dasi (Colorado State University)
Title: "Can Turbulence Really be Universal?"
Date: Friday, October 24, 2014
Time: 11:00 a.m.
Location: Gilman # 50 (Marjorie M. Fisher Hall)
The key towards fully understanding the universality of turbulence lies with better understanding the problem of intermittency, particularly for the case of turbulent shear flows (TSFs). The intermittency problem specifically refers to the highly intermittent nature of the turbulent kinetic energy dissipation rate field. These intermittent fluctuations in energy dissipation are reflected in the fluctuations of the local dissipative scale (so called smallest turbulent eddy size) giving rise to the existence of sub-kolmogorov eddies with large velocity scales. In this talk, I will discuss the statistical properties of the local dissipative scales though (a) a simple monte-carlo formulation of isotropic and anisotropic velocity fluctuations in space, and (b) time-resolved measurements of the TSF downstream of a backward facing step. We will argue through these simulations and measurements that intermittency does not obey a single universal statistical property. Instead, it appears to depend on the strength of the local mean deformation field, and therefore directly contradicting the notion of local isotropy. Nevertheless, these departures from isotropic expectations appear to be related only to the local mean-shear dissipation Reynolds number (based on the local mean turbulent kinetic energy dissipation rate and the local mean shear). The significance of this finding points to the possible existence of a family of universal small-scale structures of turbulence with the classical isotropic case being a special case corresponding to vanishing mean shear.
Lakshmi Prasad Dasi is currently Assistant Professor at the Department of Mechanical Engineering, Colorado State University. He obtained his M.S and Ph.D. in Civil and Environmental Engineering from Georgia Tech in 2000, and 2004 respectively with a focus on turbulent mixing. His bachelor’s degree is from Indian Institute of Technology, Bombay (India). His research interests include cardiovascular biomechanics, biofluid mechanics, and fluid turbulence.