Advances in output feedback control of transient energy growth in a linearized channel flow

Transient energy growth (TEG) is a primary mechanism for bypass transition in many wall-bounded shear flows. Here, we investigate the efficacy of reducing TEG in a linearized channel flow with feedback controllers that use wall shear-stress sensors and wall-normal blowing/suction actuators. Owing to established performance limitations of observer-based controller designs within the context of TEG, we study static output feedback linear quadratic regulation (SOF-LQR) strategies for control. SOF-LQR is found to outperform optimal observer-based feedback designs, and to reduce TEG of spanwise disturbances relative to the uncontrolled flow. We further show that by introducing an appropriate set of additional observables, SOF-LQR controllers can reduce TEG associated with streamwise and oblique disturbances as well. In fact, we show that by selecting a small number of appropriate observables, SOF-LQR controllers can fully recover full-state LQR performance.