Flow Separation Control with Microflexural Wall Vibrations

Abstract

A capacitively actuated active flexible wall (AFW) transducer has been developed for controlling boundary-layer flow separation. The transducer elements are first used as sensors to determine the most effective frequencies for wall actuation in the vicinity of a separating or marginally separated boundary layer. These frequencies typically result from an interaction of the flow with small-scale geometrical features of the wall. Microflexural vibratory actuation of selected regions of the transducer's flexible membrane at the aforementioned frequencies can then be used to defer separation as demonstrated in wind-tunnel experiments. The AFW transducer uses the preseparation velocity gradient at the point of actuation to amplify the microvibratory stimuli and cause it to modulate the pressure gradient. This subsequently promotes reattachment by enhancing mixing in the inflectional velocity profiles downstream. The high actuation efficiency and the ability to sense and actuate with the same hardware make the AFW transducer attractive for a wide range of practical aerodynamic problems for significantly extending the performance envelopes of fixed and rotary-wing aircraft and aircraft engines