PIV Measurements of the Flow Around Oscillating Cylinders at Low KC Numbers

The flow around cylinders of circular, square, and diamond cross-section oscillating in quiescent fluid was studied experimentally using particle image velocimetry (My). Phase-averaged measurements of the velocity field were obtained at the maximum-amplitude, zero-amplitude, and intermediate positions of the oscillation cycle. The experiments were performed at low Keulegan-Carpenter numbers, from KC = 1 to 3.5, and for moderate Stokes numbers, from beta = 250 to 376. Within this range of KC, the flow patterns remained symmetric about either side of the cylinders. For KC = 1, the flow remained close to the surface of the cylinders throughout the cycle. For KC = 1.5 to 3.5, an attached vortex pair formed behind the circular and square cylinders at the maximum-amplitude position. The distinct geometry of the diamond cylinder, with two fixed separation points, led to a unique but still symmetric vortex pattern.