Flow over an inline oscillating circular cylinder in the wake of a stationary circular cylinder

Abstract

Flow interference between an upstream stationary cylinder and an inline oscillating cylinder is studied with the lattice Boltzmann method. With a fixed Reynolds number Re=100 and pitch ratio L/D=4, the effects of oscillation amplitude A/D=[0.25, 1] and frequency f e /f s =[0.5, 2] are investigated. The wake response state is categorized into lock-in and non-lock-in. The lockin zone in the bifurcation diagram of amplitude versus frequency is discontinuous. Response states of upstream and downstream wakes are similar under the conditions of small amplitude or low frequency. However, with large oscillating parameters, the two wakes are prone to be in different states as the flow field becomes irregular. Two distinct flow regimes have been identified, i.e., single-cylinder and two-cylinder shedding regimes. The presence of single-cylinder shedding regime is attributed to the low shedding frequency of the downstream cylinder at large amplitude. Hydrodynamic forces of the oscillating tandem system are discussed. The results reveal that forces on the two cylinders behave differently and that the absence of vortices in the gap flow significantly reduces the forces exerting on the tandem system.