The Secondary Ultra-High Pressure Pulse in Gaseous Products After Complete Detonation in Near-Field Underwater Explosions

Underwater explosion phenomena involve the detonation wave generating high-pressure shockwaves and forming an expanding gas bubble in the water. Near-field underwater explosions are rarely researched due to the complex interactions among different materials. The propagation of internal load in the charge is influenced by detonation waves and the movement of the gas-liquid interface. In this work, a compressible multiphase fluid solver with energetic material detonations is developed to capture the discontinuities of shock waves and interfaces between multiphase interfaces with high density and pressure ratios. The spatial terms of the system equations are discretized using fifth-order weighted essentially non-oscillatory reconstruction in characteristic space and Lax-Friedrich's splitting, while the temporal terms are discretized using a third-order total variation diminishing Runge-Kutta scheme. The solver is validated by comparing detonation wave and shockwave pressure histories with results from other literature and theoretical solutions. Numerical results of the simulation of near-field underwater explosions show that the first ultra-high pressure pulse (exceeding 10 GPa) is formed by the detonation wave in the gaseous products region due to the release of chemical energy. The second ultra-high pressure pulse is generated after the rarefaction waves propagate to the center of the spherical gaseous products zone. When the rarefaction waves are reflected again from the center of the gaseous products bubble, the second ultra-high pressure pulse begins to form gradually. The peak pressure of the second ultra-high pressure pulse is about 150 GPa.