Study on the Collapse Behaviors of a Single Cavitation Bubble Near a Concave Wall

Abstract

ABSTRACT The enormous power emitted from cavitation bubbles has been positively utilized in drilling rate improvement and increasingly comes into prominence in oceanic hydrate recovery. Previous studies mentioned that the collapse process of a cavitation bubble near a wall is seriously affected by the wall shape. In present study, the dynamics of a single cavitation bubble near a concave wall with hydrate properties are numerically investigated. The evolutions of the bubble profile varying with the defined parameter θ have been computed. Then, the effect of θ on the bubble volume and collapse time was discussed. Moreover, the cavitation damage towards the concave wall was preliminarily revealed. The simulated results show that the shrinkage process of a cavitation bubble near a concave wall mainly includes a jet penetration stage and a collapse stage. Increasing θ leads to the reduction of bubble shrinkage rate and the extension of collapse time. With the θ varying from 0° to 180°, the pressure at wall center emitted by shock wave increases gradually, while the impinging pressure induced by micro-jet reaches its maximum when θ = 90°. The thermal effect is greatest when θ = 90° due to its higher generated temperature and micro-jet velocity. INTRODUCTION Cavitation demonstrates that the vapor bubbles occur in liquid as the local pressure decreases below the saturated pressure value (Brennen, 2014; Franc & Michel, 2006; Zhang et al., 2017). The source of severe erosion on warship propellers, hydraulic pumps and turbines originates from the collapse of cavitation bubble clouds, in which process the instantaneous high pressure and high temperature are generated (Choi & Chahine, 2016; Franc et al., 2011). Generally, when the bubbles collapse in the vicinity of a wall, they will release shock waves and micro-jets with high velocity. Once its aggressiveness exceeds the threshold determined by the material properties, it will cause deformation, pits and craters on the surface of the material (Choi et al., 2014; Hsiao et al., 2014; Pöhl et al., 2015). Although the cavitation phenomenon is undesirable in many hydraulic engineering situations, the extreme energy generated by cavitation bubbles has been positively used in some technologies. For example, the cavitation jet producing cavitation bubble in flows, has been adopted for pipes cleaning (Bukharin et al., 2020; Peng et al., 2018), drilling rate improvement (Li et al., 2002; Li et al., 2005; Li et al., 2007), and metal peening (Soyama, 2020; Soyama et al., 2011; Soyama et al., 2020).