Experimental investigation of wall-pressure fluctuations in compressible turbulent cavitating flows with emphasis on non-Gaussian features

An accurate probabilistic representation of pressure fluctuations in attached turbulent cavitating flows, especially under strong unsteady cavity regimes, i.e., cloud cavitation, is essential for the reliable prediction of cavitation loads and thus preventing potential cavitation damage. The objective of this work is to examine the wall pressure fluctuations in compressible turbulent cavitating flows, especially the non-Gaussian behaviors and their physical mechanisms. Experiments were conducted in the backward-facing wedge model installed in a high-speed water tunnel. Four high-frequency PCB pressure transducers were installed on the divergent section to capture the cavitation-induced pressure fluctuation signals. The results showed that wall-pressure fluctuations in cavitating flows present non-Gaussian features with positive skewness, and this positive skewness is independent of the cavity regime, which is an intrinsic nature of cavitating flows. However, the fluctuating pressure signals under different cavity regimes show differences. At inception and in the sheet cavity, high-frequency and low-magnitude fluctuating pressure signals are responsible for the positive skewness. At the cloud cavitation cavity, both high-frequency and low magnitude and low-frequency and high-magnitude fluctuating pressure signals are responsible for the positive skewness. In particular, when shockwave dynamics are dominant, a unique kind of fluctuating pressure signal with high frequency and large magnitude is found to be the cause. Finally, the Hilbert-Huang transform (HHT) is employed to analyze the fluctuating pressure signals in cloud cavitation, and a physical model based on cavitation bubble dynamics is proposed. The current study can help to improve the understanding of the dynamics and pressure loads of cavitation.