Effect of initial conditions on interrupted underwater multiphase flow and load response

The underwater semiclosed gas–liquid multiphase flow process and load response characteristics have been introduced in our former research [Liu et al., “Numerical investigation of the multiphase flow and loading state of underwater semiclosed initial interrupted bubbles,” Phys. Fluids 36(9), 093356 (2024)]. In this paper, the formation mechanism of water hammer impact is further improved by analyzing the change of fluid state parameters at the characteristic position inside the cylinder, and then the response characteristics of the load at different initial conditions are studied, revealing the influence law of the initial conditions on the load. First, the numerical simulation model was verified with ground simulation experiments and underwater large-depth loading experiments to simulate the initial interrupted gas–liquid multiphase flow in typical states, and the load response during the evolution of the gas–liquid phase was obtained. Furthermore, the formation mechanism of bubble pulsation and water hammer impact loading is refined in combination with changes in flow parameters. Second, the mechanism of action of initial values, such as the launcher exit depth and the initial pressure difference on the load, was investigated, and the relationship between typical parameters and the load was obtained. The results show that with increasing water depth at the launcher exit, the relative pressure change caused by bubble pulsation gradually decreases, the relative pressure change caused by water hammer impact gradually increases, and the time it takes for the two loads to peak gradually decreases. With increasing initial pressure difference between the inside and outside of the cylinder, the bubble pulsation load is positively correlated with the initial pressure difference, whereas the water hammer impact load tends to increase first and then decrease. The initial pressure difference has little effect on the period of the pulsating load of the air bubble at the cylinder, but the time it takes for the water hammer impact load to peak decreases with increasing pressure difference.