Numerical study on the cavity dynamics for vertical water entries of twin spheres

In this study, a three dimensional(3D) numerical model of six-degrees-of-freedom(6DOF) is applied to simulate the water entries of twin spheres side-by-side at different lateral distances and time intervals.The turbulence structure is described using the shear-stress transport k-ω(SST k-ω) model, and the volume of fluid(VOF) method is used to track the complex air-liquid interface. The motion of spheres during water entry is simulated using an independent overset grid. The numerical model is verified by comparing the cavity evolution results from simulations and experiments. Numerical results reveal that the time interval between the twin water entries evidently affects cavity expansion and contraction behaviors in the radial direction. However, this influence is significantly weakened by increasing the lateral distance between the two spheres. In synchronous water entries, pressure is reduced on the midline of two cavities during surface closure, which is directly related to the cavity volume. The evolution of vortexes inside the two cavities is analyzed using a velocity vector field, which is affected by the lateral distance and time interval of water entries.

圆球水面弹跳试验研究

In this paper,the fow physics and impact dynamics of a sphere bouncing on a water surface are studied experimentally.During the experiments,high-speed camera photography techniques are used to capture the cavity and free surface evolution when the sphere impacts and skips on the water surface.The infuences of the impact velocity(v_(1))and impact angle(θ_(1))of the sphere on the bouncing fow physics are also investigated,including the cavitation evolution,motion characteristics,and bounding law.Regulations for the relationship between v_(1)andθ_(1)to judge whether the sphere can bounce on the water surface are presented and analyzed by summarizing a large amount of experimental data.In addition,the efect ofθ_(1)on the energy loss of the sphere is also analyzed and discussed.The experiment results show that there is a ftted curve of v_(1)=17.5θ_(1)−45.5 determining the relationship between the critical initial velocity and angle whether the sphere bounces on the water surface.