Abstract: To study the evolution characteristics of the transient multiphase flow field formed by the underwater high-speed projectile motion, a two-dimensional unsteady multiphase flow numerical model of the underwater sealed launching muzzle was established.The VOF multiphase flow model is used to describe the two-phase interface, and the Standard k-ε turbulence model is used to describe the gas-liquid turbulent mixing. The feasibility of the model is verified by underwater launch visualization experiments. On this basis, for the 30 mm underwater gun, three types of bullets are designed: pointed, blunt and rounded, the UDF coupled interior ballistic process combined with the dynamic grid technology is used to numerically simulate the evolution process of the underwater sealed firing muzzle flow field, and the influence of three warhead shapes on the evolution characteristics of the muzzle flow field is analyzed. The result shows that the initial parameters of the muzzle under the three types of projectiles are different at the moment when the projectile is ejected. The muzzle velocity of the projectile for the condition of the conical bullet is relatively the smallest and the muzzle pressure is the highest. The muzzle velocity of the projectile for the condition of the round head bullet is the largest, and the various muzzle parameters for the condition of blunt bullet lie between the two. The Mach disk is formed at about 150 μs under blunt and round head projectiles, and the shock core region is bowl-shaped; the Mach disk is formed at about 180 μs under the condition of sharp projectile, and the shock core region is shaped like a heart.

Key words: underwater launch, transient flow field, multiphase flow, numerical analysis