Active flexible walls for efficient aerodynamic flow separation control

Abstract

I A capacitively actuated active flexible wall (AFW) transducer has been developed for controlling boundary layer flow separation. The transducer elements are first used to determ’ine the most effective frequencies for flow wall interaction in the vicinity of a iseparating or marginally separated boundary layer. These are typically one to two orders of magnitude higher than those needed for other forms of oscillatory control of separating flows. Micro-scale 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 w)ndtunnelexperiments.TheAFWtransducerusesthe pie-separation velocity gradient at the point of actuation to amplify the micro-vibratory stimuli and cause it to modulate the pressure gradient. This subsequently promotes re-attachment by enhancing mrxing 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 armraft and aircraft engines.