Interaction of a deep-water wave with a vertical cylinder at low Keulegan–Carpenter number: Transition from phase-locked modes of vortex formation

Abstract

Vortex formation from a cylinder in a deep-water wave is characterized using a technique of high-image-density particle image velocimetry for small values of wave amplitude, which corresponds to low magnitudes of the Keulegan–Carpenter (KC) number. Despite the fact that the deep-water wave involves particle trajectories in the form of circular orbits, whose axes are normal to the axis of the cylinder, it is possible to attain modes of vortex formation that are phase locked to the wave motion at lower values of KC. At a critical value of KC, however, the onset of non-phase-locked modes occurs. These modes, which are defined in terms of patterns of instantaneous vorticity, take three basic forms. Furthermore, when the cylinder undergoes self-excited vibrations at the critical value of KC, it is possible to identify the same basic modes as for the stationary cylinder.