Wake instability modes for forced transverse oscillation of a sphere

Abstract

The present numerical study aims to identify the instability modes in the wake behind a transversely oscillating sphere with amplitude A=0.5 at Reynolds number Re=300. The governing equations are solved in the non-inertial frame using the immersed boundary method. The longitudinal thread-like structure is accompanied by asymmetric shedding before the onset of a “lock-in” regime. The wake is found to exhibit symmetric vortex shedding and organized chain like structures in the synchronized regime. Lesser flow inertia at a relatively low Re is dominated by the externally applied motion of the sphere resulting in negative energy transfer by the fluid to the sphere. In the synchronous regime different timing of vortex shedding and phases of coefficient of vortex with sphere motion demarcate two wake modes which have close resemblance with the modes found in induced vibration of a sphere.