The flow past a sphere with centric cylindrical bore of different diameter and orientation

Abstract

Motivated by the potential safety hazard of cracks in flow past bluff bodies in ocean engineering applications, incompressible viscous flow past a sphere with a centric, cylindrical bore at Reynolds number of 300 is investigated by a finite volume method with adaptive mesh. The influence of bore with different Rd (the diameter ratio of the bore to the sphere, is ranged from 0 to 0.3) and orientation on the vortex shedding, flow separation and drag coefficients are analyzed. The results show that the streamwise-orientated bore has significant influence on vortex shedding (it becomes to the double-line vortex, instead of hairpin vortex at Rd≥0.25) and drag coefficients. Due to the interruption of fluid flows through the bore, it disturbs the periodicity of vortex shedding and pushes the separation bubble back away from the sphere. The crosswise-orientated bore has little effect on vortex shedding and drag coefficients, but the flow separation and the transition to the unsteady regime are delayed due to the bore closed to the separation points in (x,y)-plane. Due to the jet-like flow, the instability of the flow past a sphere is magnified when the diameter of borehole is sufficiently small (Rd=0.05), whether it is streamwise-orientated or crosswise-orientated bore.