The effect of wall and distribution parameters on the acoustic radiation of bubble clusters' near-wall collapse

This study explores the effects of wall and distribution parameters on the noise spectrum of bubble clusters during near-wall collapse. Applying direct numerical simulations and Ffowcs Williams–Hawkings (FW–H) method to evaluate sound pressure, we first discussed the selection of suitable integration surfaces and monitoring points in this special scenario. We then investigated the influence of the wall: it delays the collapse of the overall cluster, slightly suppresses the time-domain sound pressure peak, and produces an obvious negative pulse after the main peak. In the frequency domain, it will make the sound pressure component in the mid-to-low frequency band increase (for dense cluster) or decrease (for sparse cluster). Inside the bubble cluster, the effect of wall shielding may exceed the interlayer “shielding effect”. To study the influence of distribution parameters, layered and lognormal bubble clusters are arranged across volume fractions ranging from 1% to 40%. We found that the arrangement pattern and volume fraction have a generally similar influence to that in the free field. However, the wall will cause both bubble clusters to collapse faster, especially the layered cluster, and the asymmetry it brings about will make their time-domain sound pressure and noise spectra more chaotic. The decay rate of the layered clusters is lower than in the free field, while the decay rate of lognormal clusters is approximately in line with the exponential formula: Decay rate(dB/octave)=4.7790*exp(-0.0171α) . These findings investigate the impact of the wall on bubble collapse and provide a solid foundation for further studies of cavitation noise in practice.