Investigation of Microjet Injection for Reduction of Supersonic Jet Noise

Jet noise reduction is one of essential issues to realize environmentally-friendly and highly-efficient supersonic jet propulsion system. In the present study, experimental and numerical investigations were conducted in order to clarify the effect of microjet injection on supersonic jet noise. The experiments were focused on supersonic jet with Mach number up to 1.49, generated from a rectangular nozzle with high aspect ratio. The microjet injection angle was set to 90 degrees against the main jet axis. Far field measurements were conducted for the jet noise in the cases with and without microjet injection, and the noise reduction up to 7.5 dB was obtained. To study the mechanism of noise reduction, flow field visualization by schlieren technique and CFD analysis were conducted.