Control of supersonic impinging jet flows using supersonic microjets

Supersonic impinging jets, such as those occurring in the next generation of short takeoff and vertical landing aircraft, generate a highly oscillatory flow with very high unsteady loads on the nearby aircraft structures and the landing surfaces. These high-pressure and acoustic loads are also accompanied by a dramatic loss in lift during hover. Previous studies of supersonic impinging jets suggest that the highly unsteady behavior of the impinging jets is due to a feedback loop between the fluid and acoustic fields, which leads to these adverse effects. A unique active control technique was attempted with the aim of disrupting the feedback loop, diminishing the flow unsteadiness, and ultimately reducing the adverse effects of this flow. Flow control was implemented by placing a circular array of 400-mum-diam supersonic microjets around the periphery of the main jet. This control approach was very successful in disrupting the feedback loop in that the activation of the microjets led to dramatic reductions in the lift loss (40%), unsteady pressure loads (11 dB), and near-field noise (8 dB). This relatively simple and highly effective control technique makes it a suitable candidate for implementation in practical aircraft systems.