Wake structure of an oscillating cylinder in a flowing soap film at low Reynolds number

When a circular cylinder oscillates with respect to a uniform background flow, a variety of vortex wake patterns are observed as a function of the oscillation amplitude and frequency. Williamson and collaborators have determined pattern bifurcations in parameter space for 3D water flows with Re>300; Leontini and collaborators have studied the problem using a 2D computational method, which is physically relevant for Re<200. There are several differences between these prior computational and experimental results. We will present results of an ongoing experimental study of the wake structure produced by a circular cylinder undergoing forced oscillations transverse to the background flow in an inclined soap film system with Re<200. Wake patterns are observed directly and clearly via the interference fringes caused by thickness variations in the soap film. Comparisons will be made with the previous studies, and features of the two-dimensional experimental wake behavior will be explored.