Closed-loop control of an unstable open cavity

A closed loop control approach has been implemented for the case of an unstable open cavity flow. Model reduction techniques and Linear-Quadratic- Gaussian (LQG) control have been combined to stabilize the flow. A blowing/suction actuator has been placed upstream of the cavity and a skin friction sensor downstream of it. Reduced-order models based on global modes and balanced modes have been tested. We show that a reduced-order model based on the unstable global modes (to represent the unstable dynamics) and a few balanced modes (to capture the input-output dynamics of the stable sub-space between the actuator and the sensor) is optimal to stabilize the compensated system. On the other hand, it is shown that the direct and adjoint stable global modes are not appropriate to model the stable subspace due to their strong non-normality. © 2010 Springer-Verlag Berlin Heidelberg.