Experimental and simulation study of the pulsation characteristics of underwater semiclosed initial intermittent bubbles

Bubbles at the cylinder outlet are a typical feature of the underwater ejection process. The interaction between gas and water is turbulent and results in an unstable bubble interface. In this work, experimental and numerical methods were used to determine the evolution of underwater semiclosed initial intermittent bubbles and their pressure propagation characteristics. Direct measurements of the interfacial migration behaviour of the bubbles were made using a high-speed video camera, and the variation in the pressure law in the flow field was obtained using a pressure sensor. The bubble pulsation characteristics were also analysed in conjunction with numerical simulations. The results show that the bubble at the mouth of the cylinder underwent the process of expansion, contraction, necking, and fracture under the coupled effect of the inertial motion of the liquid phase and the pressure inside the bubble and exhibited obvious periodic evolution characteristics. The flow instability driven by the velocity and density gradient gradually destabilised the bubble boundary, resulting in the phenomenon of necking of the gas cluster. Simulations were carried out for different diaphragm opening states to investigate the effects of the diaphragm cracking state on bubble evolution and pressure fluctuations.