Experimental study on pressure oscillation characteristics of muzzle bubble of water-exit projectile

Water-exit projectiles with high-pressure gas ejection usually form bubbles at the muzzle of the launch tube and are non-spherical. The dynamic evolution of non-spherical bubbles in the muzzle involves complex multiphase flow, which affects the pressure load distribution in the launch tube. It is found that the muzzle bubble is affected by the water body's viscous resistance, and the pressure in the bubble shows a periodic attenuation. In this paper, the damped vibration equation is introduced, and the periodic oscillation prediction model of gas pressure in the launch tube is established, which can accurately predict the periodic change of pressure in the launch tube. When the ambient pressure is constant, the increase in muzzle pressure ratio increases the bubble's internal pressure. As the internal pressure of the bubble increases, the bubble pressure oscillation frequency decreases. In addition, the muzzle bubble is affected by high turbulence, and the bubble size has high degree of uncertainty, which introduces significant dispersion in its Strouhal number. This work can serve as a reference for the structural strength design of underwater launch vehicles.