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Article

Optimal control of transition initiated by oblique waves in channel flow.

Authors: Högberg, M., Bewley, T. R., Berggren, M, Henningson, D.S.H.
Document Type: Conference
Pubstate: Published
Journal: Turbulence and Shear Flow Phenomena - 2
Volume: I   157-161
Year: 2001

Abstract

Using two different approaches to optimal control in channel flow an effort is made to try to identify differences and similarities. One approach is to use the Navier--Stokes equations and apply a gradient based optimization technique to find the optimal control. The other approach is to make use of the linearized equations known as the Orr--Sommerfeld --Squire equations to compute the optimal control. Limiting ourselves to look only at oblique wave perturbations we compare the resulting energy evolution from application of the respective control strategies. Qualitatively the performance of the two approaches are similar, at least when they work under comparable conditions. The non-linear control can be more aggressive initially since there is no direct limitation on the time derivative of the control even though the discretization implicitly enforces some degree of penalty. Adjusting the parameters properly we can show that the control from the two approaches are very similar. Also we try to quantify the performance of the estimator based control, or compe nsation, using only measurements on the wall, compared to the full-state information con trol. The performance of the compensator is found to be good for small perturbations, especially if a good initial guess can be provided.