Investigation of bubble clouds in a cavitating jet

Abstract

It is possible for cloud cavitation to severely damage a material's surface. In this study, the unsteady behavior of cloud cavitation in a high-speed water jet is investigated by experimental observation and numerical simulations. Using a high-speed video camera with a frame rate of approximately 5 × 105 fps, it is found that high-pressure pulses are formed by collapsing bubble clouds, and that those pulses rise at a few microseconds before the cloud collapses. An erosion test is carried out by the injection of the water jet into the aluminum specimen. This test shows that the mass loss curve has two peaks and that the mass loss at the second peak located some distance below the nozzle outlet comes from the erosive property of the cloud cavitation. To explain these experimental results, two cavitation models are employed. The first is a simplified continuum model of a homogeneous two-phase flow, and the other is a spherical cloud model filled with the cavitation bubbles. The intermittent generation of the cavitating jets is simulated numerically by the first model, and the focusing effect of a spherical wave is computed by the second model. The second model reproduces the large impulsive pressure and the time lag between the pressure pulse and the cloud collapse. Some problems in the computational models are also identified by comparing them with the experimental results.