Experimental investigation of passive control for cavity noise in high-speed flow using sawtooth spoiler

The aerodynamic noise from cavity flow poses an increased risk of fatigue fracture for structures in aeronautic engineering. To address this concern, a passive control device in the form of sawtooth spoiler was positioned at the leading edge of a rectangular cavity during wind tunnel tests at Ma 0.9 and 1.5. The results obtained by pressure measurements indicated maximum reductions in both the overall sound pressure level of 9.5 dB and 4.3 dB and the tonal amplitude of approximately 18 dB and 12 dB under the two test conditions. Through the implementation of the fluorescent oil flow technique, it was verified that the lifting of shear layer is still the dominant mechanism for the reduction of cavity noise in high-speed flow. Additionally, analysis of the oil flow images observed at Ma 1.5 revealed that the local separation on the bottom wall of the controlled cavity contributed to an increase in high-frequency tonal amplitudes. Moreover, the study delved into the effects of three sawtooth parameters, namely tooth angle, tooth height, and total height. The conclusive finding was that the total height emerged as the decisive parameter influencing the performance of the sawtooth spoiler in noise control.