Analysis of ground distance effect on hypervelocity jet flow and stability of projectile in half-space

Many complex physical phenomena are involved in the firing of hypervelocity projectiles, especially near the ground. In fact, the range of influence is so wide that it is impossible to ignore the significant influence of the ground on the stability of the hypervelocity jet and the motion of the projectile. In this study, we established four three-dimensional numerical simulations under different launch conditions, including distances of 1.8, 1.5, 1.0, and 0.55 m above the ground. Taking a 300-mm-caliber counter-mass propelling gun as an example, which exhibits a characteristic flow field morphology under a velocity of 1730 m/s, we compared different flow phenomena at different heights from the ground. The results indicate that the hypervelocity muzzle shock wave is reflected by the ground and a new opposite-direction shock wave was created. The interaction between the muzzle shock wave and the new opposite-direction shock wave makes the pressure of the bottom half of the calculation domain much higher than that of the upper half. At the same time, along with the increase in pressure, which is generated on the ground, it even affects the shear layer around the projectile body. The projectile movement is disturbed by changes in lift and moment force, which alter several other parameters, such as the rotating angular velocity. Thus, the distance to the ground was found to be one of the significant influencing factors during the experiment.