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The use of data extracted from particle image velocimetry (PIV) along with vector and tensor visualization techniques provides a valuable tool for understanding a complex flow field. By studying a simple geometric structure such as a cylinder under a simple transient waveform, fundamental mechanisms of wake development under solitary wave flow can be explored using this method of flow visualization.
In order to quantify these wake formations, laboratory experiments were performed using a particle image velocimetery (PIV) system to extract velocity vector field data in the three planes of motion in the cylinder wake. Based on observations made from these images, the interaction of a cylinder with a solitary wave was categorized into three phases: 1) formation of a shear layer and generation of primary vortices, 2) generation of secondary vortices and shedding of primary vortices, and 3) migration of vortices outward and upstream of the cylinder.
A second visualization technique developed by Zhang et al. (2008) and Palke et al. (unpublished) based on asymmetric tensor analysis is applied to the velocity data to determine non-translational components (volumetric dilation, angular deformation and rotation) of the cylinder wake. This technique provides a means of visualizing and quantifying the velocity gradient tensor components of scaling, stretching, and rotation in the fluid. These images provide valuable insight into the development and dissipation of vorticity in the cylinder wake. In particular, they suggest fluid elongation perpendicular to areas of intense rotation contributing to vortex dissipation outward and in the upstream direction of the cylinder.
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