In the present work, a three-dimensional numerical model with six-degrees-of-freedom is adopted to carry out the investigation of twin water entries with two spheres side-by-side. The shear-stress transport k–ω model is used to detail the turbulence structure, and the air–water interface is tracked through the volume of fluid method. The motion of consecutive water entry with spheres is simulated using an independent overset grid technology. Numerical results reveal the variation of different kinds of lateral forces experienced by the trailing sphere following water entry, while simultaneously clarifying the governing law regarding the effects of time interval, lateral distance, and entry velocity on the trajectory behaviors. The repulsive and attractive forces are found upon the trailing sphere (sphere II) entering water, inducing different deviation directions, which are affected by the time interval and lateral distance. In addition, increasing water-entry velocity results in an increase in both attractive and repulsive force acted on sphere II; notwithstanding, the effect of repulsive force on trajectory characteristics is more noticeable.

Multiple projectiles moving in water often encounter problems such as motion disturbance from adjacent body and unsteady cavity coupling, making the flow structure and motion characteristics very complex. In this study, a computational fluid dynamics (CFD) method is employed to model two parallel supercavitating projectiles moving in water side-by-side. The cavity characteristics and flow details around the two projectiles are presented, and the variation of mutual disturbance with axis distance and flow velocity are analyzed. Numerical results show that the two cavities feature good mirror symmetry, and the influence of axis distance and flow velocity on the cavity contour is mainly reflected in the varying cavity diameter and length. It is found that the parallel projectiles repel each other at different axis distances and flow velocities. It is more easily for the parallel projectiles to achieve supercavitating motion state than a single projectile due to the flow interaction between the twin projectiles.