Motion characteristics of sphere with uniaxial through-hole after passing through air–water interface: Case study with different submergence depths

Abstract

A vented sphere with a density of 2.6 × 10³ kg/m³ and a diameter of 25.4 mm containing a circular uniaxial through-hole (diameter: 6 mm) was launched vertically upward from stationary water toward the air–water interface. The launch speed was adjusted such that the Reynolds number of the sphere was approximately 3000 immediately after it passed through the air–water interface. The effects of varying the submergence depth on the motion of the vented motion and behavior of the air–water interface were investigated. The entrained water mass increased with the submergence depth, resulting in an increase in the kinetic energy loss of the vented sphere. As the submergence depth increased, the vented sphere rotated as it passed through the air–water interface, and a sheet-like water mass was formed parallel to the direction of the through-hole. The vented sphere moved in the direction opposite to the scattering of the water mass. The vented sphere lost more kinetic energy compared to a normal sphere (without through-holes) while passing through the air–water interface at the same Reynolds number. These results indicated that the presence of the through-hole affected the motion characteristics of the sphere and behavior of the entrained water mass. These findings provide useful information for effectively controlling the attitude of artificial swimming devices that pass-through air–water interfaces.