Diffusion-driven periodic cavitation bubbling from a Harvey-type crevice in shear flows

Abstract

We experimentally and theoretically study the characteristics of hydrodynamic cavitation bubbles generated from a Harvey-type crevice immersed in near-wall shear flows of a Venturi section. In experiments, the crevice is exposed to flows with well-controlled local liquid pressure, shear rate, and far-field dissolved non-condensable gas content. Using multi-scaled high-speed imaging techniques, we are able to identify cases with and without cavitation. In most cavitation cases, we observe periodic cavitation bubbling originating from the crevice. Furthermore, we find that the frequency of the bubbling is highly sensitive to the far-field dissolved non-condensable gas content, indicating the significant role of gas diffusion in driving the periodic cavitation bubbling. Based on the experimental observations, we summarize the physical process of periodic bubbling from the crevice, which mainly includes diffusion-driven crevice nucleus growth, crevice nucleus destabilization, and cavitation bubble detachment from the crevice. Finally, starting from this physical process, we provide a theoretical explanation that quantitatively accounts for the observed cavitation threshold and frequency of bubbling in the present setup. We believe that our findings can be valuable in predicting and controlling cavitation at surfaces exposed to flows, particularly those with tiny defects such as pinholes on complex structures produced by welding or three-dimensional printing, as well as minor erosion pits on the surfaces of fluid machinery.