Supersonic cavity response to open-loop forcing

The response of a supersonic cavity to open-loop forcing with a pulsed-blowing actuator is explored experimentally. It is shown that excitation at frequencies near the Rossiter modes are amplified, while frequencies between the first two Rossiter modes are attenuated. The results clearly demonstrate that the Rossiter modes in the supersonic cavity are weakly damped (not self-excited) modes. The supersonic modes are not saturated, and do not show the kind of nonlinear interactions with the forcing modes observed in subsonic flow. These differences between supersonic and subsonic flows are consistent with previously developed models of cavity oscillations, and the results suggest that linear techniques for the design of closed-loop controllers may be particulary effective for supersonic flows. For the flow regime studied, the oscillatory component of open-loop forcing does not play a significant role in the suppression mechanism in supersonic cavity flows.