Feedback control to prevent or delay transition in two-dimensional parallel shear flows

Feedback gains derived from balanced truncation of the respective two-dimensional linearized models for the channel and mixing-layer flows reveal spatial patterns similar to Orr structures -- the transient vortical features responsible for energy amplification in shear flows. These gains oppose such structures, providing a physically interpretable mechanism by which optimal control suppresses disturbances and delays transition in these shear flows.