At transonic velocity, ejector nozzles require third auxiliary intake valves to increase air intake, resulting in good thrust performance. However, different intake structures will inevitably lead to different internal flow-field structures and thrust performances. To evaluate the differences between nozzles with full-open valve and open-close valve at transonic velocity, we established two numerical simulation models to analyze the flow-field structure and thrust performance in the ejector nozzle. The results show that at the transonic flight state ( Ma = 1.2 ), the mainstream of the two models always maintains an overexpansion state, and the primary flow fields are highly similar. However, the secondary and the third auxiliary flow fields are significantly different. Notably, in the nozzle with open-close valve, a lateral flow occurs near the wall of the nozzle tail, resulting in several vortexes. Contrarily, in the nozzle with full-open valve, there is almost no lateral flow or vortex. Further, we found that the secondary flow tends to roll up toward the third auxiliary valve instead of directly flowing into the nozzle. Thus, the thrust coefficients of the two nozzles differ.

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.

As one of the main methods to study the characteristics of an object, experiment is the main way to verify the correctness and reliability of numerical results. The hypersonic projectile near the ground launch involves many complex physical phenomena, so the ground surface has an important impact on the flight stability of the projectile and the structural characteristics of the gas flow field. In this paper, we carried out a whole process experiment of a hypersonic projectile from the bottom of the tube to the muzzle based on the 300 mm balance gun. The muzzle pressure and the initial velocity of the muzzle were monitored by the data acquisition system. We obtained the influence of the ground on the gas flow field of the hypersonic projectile through the overpressure data on the ground near the muzzle. Meanwhile, the dynamic characteristics of the launch process are recorded by high-speed photography. The experimental results show that the muzzle shock wave meets the ground, and the reflection phenomenon occurs, forming a wavefront with opposite directions of propagation. It makes the pressure in the lower half of the domain significantly higher than that in the upper half. By analyzing the experimental phenomena and experimental data, this paper shows the development characteristics of the projectile’s flow field, as well as the influence of the ground on the flow field and the motion stability of the projectile.