Prediction of cavitation erosion and residual stress of material using cavitating flow simulation with bubble flow model

Abstract

We have developed a numerical simulation code that can predict the cavitation erosion and the residual stress of a material, which are both closely related to plastic deformation. The shock wave generated at the cavitation bubble collapse hits the material surface and the impact energy causes plastic deformation which changes the residual stress. When the impact energy is high, mass loss (i.e., erosion) occurs after the plastic deformation stage. We numerically simulated impulsive bubble pressures that varied on the order of a microsecond in the cavitating flow with the ‘bubble flow model’. The bubble flow model simulates the abrupt time-variations in the radius and inner pressure of bubbles based on the Rayleigh-Plesset equation. Although the shock wave propagation was not simu- lated, the impact energy was estimated based on the bubble pressure. The pre- dicted impact energy was compared with the distribution of plastic deformation pits, which were observed on the impeller blade surface of a centrifugal pump. The predicted impact energy was also compared with the distribution of residual stress measured on a stainless steel plate after a cavitating jet impinged on the plate. The distribution of the impact energy corresponded qualitatively to that of the residual stress improvement caused by the plastic deformation. High correlation between the predicted impact energy and the plastic deformation of material was confirmed, and we found that our numerical method is relevant for the prediction of cavitation erosion and residual stress on a material surface.