Numerical study of underwater explosion bubble dynamics based on a six-equation model

In this study, a six-equation numerical model combined with a tangent of hyperbola for interface capturing (THINC) interface sharpening method is established to simulate the underwater explosion (UNDEX) bubble pulsation and jet process. The six-equation pressure non-equilibrium model was employed as a numerical model to describe the multiphase problem of UNDEX. In this study, the combination of the THINC interface sharpening technique with the volume fraction transport equation of the six-equation model is employed. During the MUSCL-Hancock method (MHM) reconstruction step, THINC reconstruction is applied to the volume fraction distribution within each cell, effectively achieving interface sharpening and reducing diffusion at the interface. Using the interface sharpening model, UNDEX numerical investigations were conducted under free-field and various boundary conditions. By comparing with the UNDEX experimental results, it was demonstrated that the numerical model accurately predicts the dynamics of bubble expansion, contraction, and jetting. The effects of buoyancy parameter δ and stand-off distance γm on the migration and jetting process of UNDEX bubbles were further studied. The results show that there are three distinct jetting patterns under the effects of buoyancy and the free surface Bjerknes force: downward jetting, neutral collapse, and upward jetting. When the stand-off distance parameter γm is large enough, the direction of the bubble jet obtained from the numerical model is consistent with the prediction results of the Blake criterion. However, when γm≤1, the Blake criterion fails, and the bubble evolution process can be predicted through the numerical model established in this study.