Motion of a cylinder adjacent to a free-surface: flow patterns and loading |
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Authors: | Q Zhu J -C Lin M F Unal D Rockwell |
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Institution: | (1) Department of Mechanical Engineering and Mechanics 354 Packard Laboratory, 19 Memorial Drive West Lehigh University Bethlehem, PA 18015, |
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Abstract: | The flow structure and loading due to combined translatory and sinusoidal motion of a cylinder adjacent to a free-surface
are characterized using a cinema technique of high-image-density particle image velocimetry and simultaneous force measurements.
The instantaneous patterns of vorticity and streamline topology are interpreted as a function of degree of submergence beneath
the free-surface. The relative magnitudes of the peak vorticity and the circulation of vortices formed from the upper and
lower surfaces of the cylinder, as well as vortex formation from the free-surface, are remarkably affected by the nominal
submergence. The corresponding streamline topology, interpreted in terms of foci, saddle points, and multiple separation and
reattachment points also exhibit substantial changes with submergence. All of these features affect the instantaneous loading
of the cylinder. Calculation of instantaneous moments of vorticity and the incremental changes in these moments during the
cylinder motion allow identification of those vortices that contribute most substantially to the instantaneous lift and drag.
Furthermore, the calculated moments are in general accord with the time integrals of the measured lift and drag acting on
the cylinder for sufficiently large submergence.
Received: 18 May 1998/Accepted: 18 August 1999 |
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