Free-Surface Wave Interaction with a Horizontal Cylinder: Effect of Nominal Submergence of Cylinder beneath Sree-Surface
Peter Oshkai
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Department of Mechanical Engineering > University of Victoria
Free-surface wave interaction with a horizontal cylinder: effect of nominal submergence of cylinder beneath free-surface.
Instantaneous patterns of vorticity are compared for two values of nominal submergence of the cylinder, h/D = 0.55 and 0, at the same frame numbers N = 11 and 15 of a cinema sequence. At h/D = 0, the quiescent elevation of the free-surface is coincident with the upper surface of the cylinder.
For the deeper submergence h/D = 0.55, frame number N = 11 reveals that the layer of vorticity concentrations B and D moves to the left away from the surface of the cylinder, giving rise to a large-scale vorticity concentration B, D at N = 15. Simultaneously, a vorticity concentration A' is formed from the left surface of the cylinder. During these events, vorticity concentration A moves along its orbital trajectory about the cylinder.
When the submergence of the cylinder is sufficiently shallow, corresponding to h/D = 0, it penetrates the free-surface during a portion of the wave cycle. As a result, the processes of vortex formation from the cylinder are delayed. Vorticity concentration A forms from the bottom, rather than the top, surface of the cylinder at N = 11 and, as evident in frame N = 15, is rapidly swept to the left. In the meantime, a pronounced concentration of vorticity A' forms from the lower left surface of the cylinder. Vorticity concentration D, originally formed on the left side of the cylinder at N = 11, migrates to the left, away from the cylinder, and simultaneously induces a counter vortex E of opposite sense from the free-surface. These events lead to the remarkable formation of six counter-rotating concentrations of vorticity at N = 15.
P. Oshkai and D. Rockwell.
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poshkai@me.uvic.ca