Abstract: Complex unsteady flow characteristics and flow-field structures occur in a high speed flow past open cavities, such as fluctuating pressure and velocity. Some sound pressure level (SPL) inside the cavities can reach 170 dB, which may damage certain installed apparatuses inside the cavity and its structural components. Noise suppression for open cavities is therefore a focus of research. This paper presents an analysis of the aero-acoustic characteristics inside an open cavity of a length-depth ratio (L/D) of 6 with or without a zero-net-mass-flux jet at Mach numbers of 0.9 and 1.5. The suppression effects of different zero-net-mass-flux jets on aerodynamic noise are discussed by analyzing the sound pressure level distribution on the centerline of the cavity floor and the sound pressure frequency spectrum (SPFS) characteristics at different measurement points. The results indicate that the jet can suppress aerodynamic noise inside the cavity, and that, at a Mach number of 0.9, it is more effective in SPL reduction in the front range of the cavity than in the rear. The suppression effect of the jet on the aerodynamic noise within the cavity is better when its exit is on the cavity-fore-face, with its direction parallel to the free-stream, than when its exit is in front of the cavity-fore-face with its direction vertical to the free-stream. The jet has little effect at a Mach number of 1.5.

Key words: cavity, zero-net-mass-flux jet, aerodynamic noise, suppression method, sound pressure level, sound pressure frequency spectrum