Resolvent analysis based jet-noise-reduction of a biconical tactical jet nozzle

The intense noise radiated by the exhaust nozzles of jet aircraft lead to sound-induced structural vibration, fatigue and personnel-related operational difficulties on board aircraft carriers. Experimental, theoretical, and computational investigations into the physics and control of jet noise have identified several important sound sources, including wavepackets, screech, Mach wave radiation, and broadband shock associated noise. Reducing the loudest sources of jet noise, without sacrificing propulsive performance, has relied on intuition, parametric survey, or optimal control techniques. With the aim of developing a more general and robust method of jet noise reduction, we present a physics-based approach, built upon a linear resolvent analysis, and apply it to reduce the noise generated by subsonic jet flow through a straight nozzle. Our approach identifies optimal forcing/response modes of the compressible Navier-Stokes operator, linearized about a jet base-flow, that best disrupt the coherent structures which are primarily responsible for the production of jet noise. Additionally, the effect of flow-discontinuities on these optimal forcing/response modes is investigated, to better understand how to extend such an approach to supersonic shock laden jets.