Jet noise reduction is essential for next-generation environmentally-friendly supersonic transport. In the present study, experimental and numerical investigations were performed to clarify the effect of microjet injection on supersonic jet noise and flow field. The experiments were focused on supersonic jet with Mach number up to 1.39, issuing from a rectangular nozzle with high aspect ratio.
The experiments varied several parameters including main nozzle pressure ratio, total pressure of microjet, number of microjets and microjet injection angle. Far-field sound pressure measurement was performed, and the characteristics of noise reduction, including its directivity, were investigated. On the other hand, the flow field was visualized with a Schlieren technique in order to understand the mechanism of noise reduction. The unsteady behavior of the shock structure and the shear layer were investigated based on the visualization results. To investigate the effect of microjets on the 3-dimensional flow field, steady RANS analysis of the flow field was performed under various conditions of the main jet and the microjets.