EE Seminar: Prof. Jason L. Speyer

~~(The talk will be given in English)

Prof. Jason L. Speyer
Mechanical and Airspace Engineering Department, University of California, Los Angeles
Thursday, December 25, 2014
11:00 - 12:00
Room 011, Kitot Bldg., Faculty of Engineering

A System Theoretic Approach to the Feedback Control of Channel Flow
Abstract
A framework for determining feedback controllers for the stabilization of three-dimensional channel flow with wall pumping-and-suction control and wall shear measurements is developed using a control theoretic approach.  The elements of this approach are the determination of the finite-dimensional model based on the Navier- Stokes equations and the controller development based on the inherent decomposition of the system state and measurement model. Using balanced realization, the model reduction of the nonnormal Orr-Sommerfield system shows the sensitivity of the transfer function and the effect of the pseudo-spectrum due to the balanced model truncation. Finally, it is shown that an upstream travelling wave reduces friction drag, but induces secondary instabilities.  It is shown that the dynamics of the steady-state flow induced by a traveling wave must be linearized and decomposed in a frame of reference moving with the traveling wave. The resulting linear time-invariant equations are appropriate for system theoretic feedback control synthesis. A linear controller based on these equations is shown to suppress the secondary instabilities in direct numerical simulations. Although our ultimate goal of driving a turbulent boundary layer to a laminar boundary layer has not yet been achieved, these various steps appear to be bringing us closer to this goal.