Two Surprising Links Between Convection Velocities and Non-Linearities in Wall-Bounded Turbulence

A Warren Distinguished Lecture with
Ian Jacobi

Aerospace Engineering, Technion Israel Institute of Technology

ABSTRACT
Coherent large-scale motions in turbulence are major contributors to important environmental flow phenomena, from river sediment dynamics and wind farm power fluctuations, to heat and momentum transport near the ground or along ocean waves. Determining the convection velocities of these large-scale motions is crucial for inferring their spatial structure from temporal field measurements; for developing mode-based models for turbulence prediction; and for developing new actuation schemes for controlling turbulent flows. In this talk, I will explore two surprisingly divergent aspects of the convection velocities of large-scale structures in turbulence. I will first show how accounting for non-linear interactions broadens the predicted spectrum of convection velocities in turbulence modeling, and then, contrariwise, how convection velocity variations can easily be mistaken for evidence of non-linear interactions. The first problem will be examined through laboratory experiments and modeling and has implications for developing more accurate predictions of the space-time spectrum of turbulence. The second problem is an analytical re-examination of the widely used amplitude modulation coefficient but has broader implications for identifying non-linear dynamics in any experimental system. 

SPEAKER
Ian Jacobi is an Associate Professor in the Department of Aerospace Engineering at the Technion Israel Institute of Technology. His research focuses on experiments and modeling of turbulent wall-bounded flows, including the fundamental structure of turbulence, drag reduction techniques, and the dispersion and clustering of particles in turbulent flows. Jacobi received his Ph.D. from Caltech in 2012, after which he held a post-doctoral fellowship at Princeton University before joining the faculty of the Technion in 2014. When he was on sabbatical, he worked at the St. Anthony Falls Laboratory at UMN.