application of wavenumber-frequency method for characteristic frequency prediction of cavity noise at subsonic speeds

Flow-acoustic feedback is one of the main types of noise in a cavity, is caused by the instability of the cavity shear layer and is enhanced through an acoustic-wave feedback mechanism. the flow characteristics of the cavity boundary/shear layer and the characteristic frequencies of the flow-acoustic feedback in the cavities are studied numerically, with aspect ratios ranging from 1/2 to 4/3. the freestream mach number is equal to 0.11, corresponding to an re-based cavity length of 2.1 ×105. improved delayed detached eddy simulations combined with ffowcs williams-hawkings acoustic analogy are used to simulate the flow and noise characteristics of the cavities. auto-correlation analysis of flow field fluctuations is used to establish a link between the boundary/shear layer pressure fluctuations and flow-acoustic feedback noise. for the low aspect ratio cavities investigated in this paper, convection velocities along the shear layer development direction are obtained using wavenumber-frequency analysis. the deeper the cavity, the lower the shear layer flow velocity. correspondingly, the characteristic frequencies of the narrowband noise generated by the flow-acoustic feedback shift linearly toward the low frequency band as the cavity depth increases. the results of the predicted noise characteristic frequencies obtained using wavenumber-frequency analysis and rossiter’s empirical formula are in agreement with the calculated results.