Numerical Investigation on the Mean Flow Fields Generated by an Oscillating Sphere

This work represents an attempt to provide an in-depth understanding of the three-dimensional flow physics related to the characterization of streaming flows due to the oscillating spherical body. The presence of any structure at sea will impact the local hydrodynamics of the site and therefore the local sediment dynamics. When a body oscillates while immersed in a quiescent fluid, the effects of their dynamic interaction are evident not only on the forces acting on the body but also on the flow field deformation by generating a non-zero mean flow. Thus, in many ocean engineering applications, it becomes necessary to understand not only the instantaneous events such as the wave-generated hydrodynamic forces acting on the structures but also the mean hydrodynamic pressure fields and fluid velocity fields. The non-linear streaming flows produced by an oscillating sphere driven in unidirectional simple harmonic motion in a quiescent fluid have been investigated. A comprehensive parametric study has been undertaken over a range of oscillatory Reynolds number and amplitude ratio and a quantitative assessment of the relation between the mean flows and the Lagrangian particle drift associated with the flow has been carried out. It is shown that while an inner mean viscous boundary layer flow is generated that is confined to a very small region near the sphere, a large mean outer vortex flow is generated that can extend a long way from the sphere along the axis of oscillation.