Experimental study on cavity flow and splash crown of porous hollow sphere during water entry

Porous hollow sphere is a hollow sphere with holes arranged in a certain pattern inside. This article presents the results of the porous hollow sphere during water entry using high-speed photography technology. The main consideration is the influence of initial velocity and hole size on the evolution characteristics of cavity flow, splash crown, and jet. Due to the presence of obvious non-chamfered holes, the porous hollow sphere still generates significant cavities when vertically penetrating into water at a lower initial velocity. Meanwhile, it generates unique cavity and the crown which has obvious columns, with the same number of cavity columns as the holes in the middle of the porous hollow sphere. During water entry, there is a jet in the middle position at the top of the sphere. When the pinch-off phenomenon occurs, there is still a jet at this position, which keeps the upper and lower cavities in contact. The shape of the cavity changes from hyperbolic to triangular and then to W-shaped. As the initial velocity increases, the contour of cavity column becomes less distinct, the surface of cavity becomes smoother, and the number of cavities at the top of the porous hollow sphere increases after cavity closed.