CAVITATION EROSION MECHANISM: NUMERICAL STUDY OF THE INTERACTION BETWEEN PRESSURE WAVES AND VAPOR BUBBLES

Abstract

Abstract Investigations on vapor bubble collapses dynamic were carried out by three-dimension simulations with the software Prototype Homogène Code_Saturne. The code solves, by applying a compressible homogeneous approach, the Euler’s equations coupled with transport equations (for the volume, mass and energy fractions) that model the phase changes and the thermodynamic effects. To close the system, the Stiffened Gas EOS (equation of state) was applied to link the pressure and the temperature to the internal energy and the density. Different mesh types and computational domains were tested to study four configurations in water: a) the vapor bubble collapse in free-field case; b) the vapor bubble collapse near a solid wall; c) the collapse of a vapor bubble in free-field case and impacted by an external pressure wave; d) the collapse of a vapor bubble placed near a solid wall and impacted by an external pressure wave. Pressure waves generated during these bubble implosions were studied and characteristic parameters (such as wave passage time and amplitude of the pressure peak applied at the solid wall) were calculated under different hydrodynamic conditions. Simulations led to some expected phenomena such as: the bubble asymmetrical shape evolution when a rigid wall is present; observation of toroidal vapor cavities; generation of high amplitude pressure waves during bubble collapses and rebounds. Original results obtained concern mainly the study of the interaction between external pressure waves and collapsing vapor bubbles. Analyses on the influence of the incoming external pressure wave amplitude on the bubble collapse time and on the pressure peak reached on the wall are also presented in the paper. The numerical study showed an amplification of the collapse pressure by the incoming pressure wave. This interaction mechanism between pressure waves and vapor structures leading to pressure amplitude amplification could be responsible for the material damages due to cavitation.