The flow around a forced cylinder between two parallel walls

Abstract

The vortex induced vibrations of a cylinder tightly confined in a narrow channel were numerically studied in two dimensions. Attached to a linear spring and subject to hydrodynamic forces and torques, the circular cylinder is free to move in both the cross-flow and in-line directions as well as to rotate about its axis. Low mass ratios and moderate Reynolds numbers were considered. The cases where boundaries, either physical or numerical, are far from the cylinder have deserved much attention, and share some of the phenomenology observed in the system here studied. As the upstream flow is increased, the tightly confined system shows an initial branch, followed by a synchronization or lock-in region that ends in a decoherence region. Nevertheless, within the lock-in region, no clear upper and lower branches appear when the cylinder is placed in a narrow channel, instead the system's behavior sensibly depends on the mass ratio. We managed to find a modified Strouhal parameter that collapses the range of excitation for the reduced masses considered and suggests a scaling for the system's natural frequency in the medium. Results offer a portrait of the motion, forces, and flow around the cylinder under such constrains.