Active closed-loop control of supersonic impinging jet flows using POD models

Fluid-flows exhibit pronounced acoustic resonances when a jet emerges from an orifice and impinges on an edge. One instance where such resonances, which are denoted as edge-tones, are produced is in a high speed jet from a STOVL aircraft nozzle impinging on the ground. Considerations of lift-loss, acoustic fatigue of nearby structures, and ground erosion mandate reliable and uniform reduction of these impingement tones during landing conditions. Elsewhere, it has been shown that microjets located at the jet nozzle serve as effective actuators for the control of impingement tones. In this paper, a closed-loop control strategy for articulating the microjet pressure is suggested, in order to maintain a uniform, reliable, and optimal reduction of these tones over the entire range of operating conditions. This strategy is based on a proper orthogonal decomposition (POD) analysis of the pressure distribution along the azimuthal direction, where the microjet pressure distribution is matched to that of the dominant POD mode of the pressure. Preliminary experimental results from a STOVL supersonic jet facility at Mach 1.5 show that the mode-matched closed-loop strategy provides an additional 8-10 db reduction, compared to an open loop one, at the desired operating conditions.