Wind tunnel experimental study of self oscillation feedback flow field structure and flow induced aeroacoustic for open cavity at low speed

Regarding the noise problem caused by open-cavity self oscillation,an experiment of flow over a rectangular cavity with a length-to-depth ratio of 2 at Mach 0.1,0.15,0.2,0.25 was conducted in the 0.55 m×0.4 m aero-acoustic wind tunnel.In this research,the velocity field and self-oscillation aeroacoustic formation mechanism was studied.High frequency Particle Image Velocimetry was employed to observe the flow field structure,the path of acoustic wave and pressure wave was analyzed.The acoustic self-sustaining oscillation modes and duct modes were investigated by testing the far sound field and the fluctuating wall pressure.Moreover,the characteristics of the correlation between the wall pressure and the acoustic performance were discussed.The results showed that apart from the main vortical structure,there are the shear vortex at the leading edge and the crash vortex at the trailing edge.Also,around the frequencies of 875 Hz,1,288 Hz,1,875 Hz and 2,050 Hz,there exists an obvious tonal noise,induced by the cavity oscillation.In addition,it was found that the wall pressure is highly correlated with the far field noise,and the tones appear at the same frequencies where the peaks show up in the wall pressure spectra.