Deep Water Wave Interaction with a Stationary Vertical Cylinder

Deep Water Wave Interaction with a Stationary Vertical Cylinder. A deep water wave incident upon a stationary vertical cylinder is represented in the schematic of the image layout. A dual CCD camera system simultaneously records images in order to minimize the effects of image blockage due to the tip of the long cylinder. These synchronized dual camera images are then spliced to yield a single, instantaneous image.

     
Patterns of instantaneous vorticity are shown at the same phase N = 1 of the instantaneous wave position, i.e., the location of the crest of the wave relative to the axis of cylinder, at three different values of Keulegan-Carpenter number KC = 2.49, 5.06 and 6.16.  These values of KC are essentially representations of the wave amplitude.  Despite this variation of KC, the patterns of vortical structures in the near-wake have a fundamentally similar form.  At KC = 2.49, concentrations A and C, which were formed during a previous portion of the wave cycle, are located immediately adjacent to concentrations B and D, which are in the process of formation. As indicated, the wave velocity Uw is directed from left to right.  The same overall pattern  of the near-wake vorticity concentrations A, C and B, D, and their locations relative to each other, persist for the higher values of KC.  At KC = 5.06, however, the scale and circulation of these vorticity clusters is larger, and the centroids of A and C are located further downstream, relative to the lowest value of KC = 2.49.  This same overall structure is evident at the highest KC = 6.16.  These investigations of the near-wake structure past a stationary cylinder serve as a basis for characterization of the patterns of vorticity associated with  quasi-one-dimensional and two-dimensional oscillations of the cylinder.