Vortex patterns in the wake of a transversely oscillating circular cylinder at low Reynolds number

The flow patterns that form in the wake of an oscillating cylinder give us important information about the nature and extent of vortex-induced vibrations (VIV) of cylindrical structures such as oil risers, power lines and undersea cables. To investigate these patterns at low Reynolds number, we oscillated a circular cylinder transversely to a uniform free stream in a gravity-driven soap film over a large portion of the frequency-amplitude parameter space and visualized the resulting wakes using a high-speed camera. A rich variety of vortex patterns were found in the primary synchronization region of the parameter space, including the 2S, 2P, P+S, 2T and coalescing wake patterns. The presence of 2P wakes in a (nominally) two-dimensional flow suggests that spanwise instabilities in the cylinder wake are not necessary for the formation a 2P wake, since these instabilities are suppressed in our experiments. We will discuss these results, as well as the results of a follow-up study involving the oscillation of an extremely thin circular disk, instead of a cylinder, which was conducted to test alternative hypotheses for the formation of the 2P wake.