Event Details
Dynamics and Control of Wall-bounded Shear Flows
Speaker: Mihailo Jovanovic, University of Minnesota
Department: Mechanical & Aerospace Engineering
Location: Bowen Hall Auditorium 222
Date/Time: Friday, October 26, 2012, 3:30 p.m. - 4:30 p.m.
Understanding and controlling transition to turbulence is one of
the most important problems in fluid mechanics. In the first part
of the talk, techniques from control theory are used to examine the
early stages of transition in wall-bounded shear flows. We
demonstrate high sensitivity of the flow equations to modeling
imperfections and show that control theory can be used not only to
design flow control algorithms but also to provide valuable
insights into the transition mechanisms.
In the second part of the talk, we examine the efficacy of
streamwise traveling waves generated by surface blowing and suction
for controlling the onset of turbulence in a channel flow. For
small amplitude actuation, we utilize weakly-nonlinear analysis to
determine base flow modifications and to assess the resulting net
power balance. Sensitivity analysis of the velocity fluctuations
around this base flow is then employed to design the traveling
waves. Our simulation-free approach reveals that, relative to the
flow with no control, the downstream traveling waves with properly
designed speed and frequency can significantly reduce sensitivity
which makes them well-suited for controlling the onset of
turbulence. In contrast, the velocity fluctuations around the
upstream traveling waves exhibit larger sensitivity to
disturbances. Our theoretical predictions, obtained by perturbation
analysis (in the wave amplitude) of the linearized Navier-Stokes
equations, are verified using simulations of the nonlinear flow
dynamics. These show that a positive net efficiency as large as 25%
relative to the uncontrolled turbulent flow can be achieved with
downstream waves. We conclude that the theory developed for the
linearized flow equations with uncertainty has considerable ability
to predict full-scale phenomena.
Bio:
Mihailo R. Jovanovic (www.umn.edu/~mihailo) is an Associate
Professor of Electrical and Computer Engineering at the University
of Minnesota, Minneapolis, where he also serves as the Director of
Graduate Studies in the interdisciplinary Ph.D. program in Control
Science and Dynamical Systems. He has held visiting positions with
Stanford University and the Institute for Mathematics and its
Applications. His current research focuses on sparsity-promoting
optimal control, dynamics and control of fluid flows, and
fundamental limitations in the design of large dynamic networks. He
is a member of IEEE, APS, and SIAM and has served as an Associate
Editor of the IEEE Control Systems Society Conference Editorial
Board from July 2006 until December 2010. He received a CAREER
Award from the National Science Foundation in 2007, an Early Career
Award from the University of Minnesota Initiative for Renewable
Energy and the Environment in 2010, and a Resident Fellowship
within the Institute on the Environment at the University of
Minnesota in 2012.