Numerical prediction of cavitation inception radiated noise of contra-rotating propeller with non-uniform inflow

Cavitating inception tonal components and broadband noise of a contra-rotating propeller in the behind-tail condition are predicted numerically by the hybrid method and validated by cavitation tunnel test. The multiphase flow transient simulations, including unsteady Reynolds-averaged Navier-Stokes (URANS) method, scale-adaptive simulation (SAS) and detached eddy simulation (DES), are used to calculate the fluctuated cavity volume and fluctuating pressure on both fore and aft propellers that acting as main noise sources. The pulsating spherical bubble radiated noise theory and directly boundary element numerical acoustics are adopted to obtain the cavitation noise spectrum. In this process, both the effects of calculational precision of source fluctuations in the flow on noise prediction and the cavitation inception on propeller noise are investigated. Besides, four sufficient conditions to determine the cavitation inception are put forward initially. Results show that, the predicted open water performances agree very well with the experimental data over a big region of advance ratios. Tile SAS presents a comparable ability to DES to predict the fluctuating pressure of contra-rotating propeller, and then serves satisfactory to unsteady load noise prediction, whereas the URANS is slightly less but still being appropriate for the low frequency noise. The prediction error of line spectrum in 800 Hz induced by fluctuated cavity volume is smaller than 4 dB, and the averaged error of spectrum level in each 1/3 Octave band is less than 1.5 dB in the region of 800 Hz to 3 kHz associated with being smaller than 2.4 dB for the total sound pressure level. A ratio less than 2% of the cavity area to disk plane of fore propeller, in conjunction with the global force variables and pressure coefficient distribution around the tip section nearly unaltered compared to that of non-condition, and the increase of noise spectrum about 8-10 dB in the mid and high frequency areas can be used to determine the cavitation inception considering both the visualand acousticcriteria at the same time. Based on this research, the two technical challenges concerning cavitation inception determination and the inception noise prediction for contra-rotating propeller in wake have been overcome, which can be greatly benefited to new torpedo design with high speed and low noise.