Experimental and numerical investigations on the transient impact load of the oblique water entry of the concave-nose projectiles

During the landing and recycling on the sea surface of a spacecraft or rocket, a concave structure may impact on the water surface. In the present paper, we experimentally and numerically analyze the multiphase flows and transient impact load during the oblique water entry of the concave -nose projectile. The projectiles used in the experiments consist of a main body that embeds an acceleration measurement system, and a transparent concave -nose. Firstly, free surface evolutions and cavity dynamics are given for the concave -nose projectile, which shows significant changes compared with the projectile without concave -nose. A special jet inside the concave -nose during the formation of the air -entertainment cavity is observed. Subsequently, it is found that compared with the projectile without concave -nose in the early stage. The increase rate of the axial force of the concave -nose projectile is slower and the force curve has a steep drop stage, then they enter the uniform reduction stage. As the concave depth increases, a 'double -peak' phenomenon on the axial force curve appears. It is found that the force peak is transferred to a single peak with increasing the impact velocity. The force peak of the concave -nose projectile is greater than the projectile without concave -nose. Besides, with increasing the concave depth, the maximum axial force of the concave -nose projectile increases firstly, and then decreases. When the ratio of concave depth to inner diameter is greater than 2, the influence of concave depth on the peak value of axial force is small. Moreover, the pressure distributions of the fluid domain and the concave -nose are analyzed to reveal the mechanism of the variation of the force peak. The study is able to provide a basic reference for the analysis of the recycling of the rocket, aircraft, etc.