ACTIVE STABILIZATION OF A PLANAR JET IMPINGING ON A FLEXIBLE WEDGE

Abstract

Feedback control is used to suppress the “ lock-in” vibration and the pressure pulsation generated by an unstable planar jet impinging upon a flexible wedge (or edge). First, the lock-in vibration to be controlled is shown to be caused by the coupling between a robust “ jet-edge oscillator” and a resonant vibration mode of the wedge. Since the system oscillation is controlled by the resonant response of the wedge, the frequency of oscillation within the lock-in range can deviate substantially from the natural frequency of the “jet-edge oscillator”. In order to counteract the upstream effect resulting from the wedge vibration, an adaptive digital controller is used to activate loudspeakers focused on the jet exit. The paper describes the system response as the lock-in vibration is gradually suppressed. When the vibration signal was used to activate the controller, the edge vibration was substantially reduced, but the jet oscillation switched to the natural oscillation mode of the jet-edge oscillator, resulting in only a slight reduction in the pressure amplitude. However, when the pressure signal was used to activate the controller, the vibrations and pressure oscillations were entirely suppressed without destabilizing other modes of the system.