Numerical investigation on underwater explosion shock wave and cavitation characteristics in heterogeneous fluid

Due to the combined action of the oceanic climate and environmental factors, there often exist the sound speed thermocline regions in the real ocean environment. The abrupt change of the sound speed would affect the amplitude and propagation trajectory of underwater explosion (UNDEX) loading. However, the effects of the fluid heterogeneity on the UNDEX loading are not fully understood. In this study, based on the local discontinuous Galerkin (LDG) method, the axisymmetric calculation model for the UNDEX loading in the heterogeneous fluid is established. Unlike the previously developed UNDEX loading models in the homogeneous fluid, the influence of the sound speed gradient is considered in the LDG governing equation. The continuity conditions about the dynamic pressure and flux are adopted to compute the numerical fluxes at the sound speed discontinuous interface, which can ensure the energy conservation property. By comparing with the standing wave and traveling wave benchemarks and UNDEX shock wave propagation case, the effectiveness of the present model in solving wave propagation problems is validated. Using this model, the effects of the sound speed discontinuous interface and sound speed gradient on the UNDEX loading and cavitation characteristics near the free surface are investigated. It can be found that the UNDEX incident shock wave would form the reflection and refraction phenomenon at the sound speed discontinuous interface. With the increase of the fluid sound speed, the pressure peak of the incident wave would decrease and the cavitation effects would be weakened. In the heterogeneous fluid with the sound speed gradient of -10 s^-1, the first pressure peak at the test point would increase by 8.45% and the cavitation duration would increase by 16.67% compared with the homogeneous fluid case.