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Experimental study of the wake behind a surface-piercing cylinder for a clean and contaminated free surface

Lang, Amy Warncke and Gharib, Morteza (2000) Experimental study of the wake behind a surface-piercing cylinder for a clean and contaminated free surface. Journal of Fluid Mechanics, 402 . pp. 109-136. ISSN 0022-1120. doi:10.1017/S0022112099006722.

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This experimental investigation into the nature of free-surface flows was to study the effects of surfactants on the wake of a surface-piercing cylinder. A better understanding of the process of vorticity generation and conversion at a free surface due to the absence or presence of surfactants has been gained. Surfactants, or surface contaminants, have the tendency to reduce the surface tension proportionally to the respective concentration at the free surface. Thus when surfactant concentration varies across a free surface, surface tension gradients occur and this results in shear stresses, thus altering the boundary condition at the free surface. A low Reynolds number wake behind a surface-piercing cylinder was chosen as the field of study, using digital particle image velocimetry (DPIV) to map the velocity and vorticity held for three orthogonal cross-sections of the flow. Reynolds numbers ranged from 350 to 460 and the Froude number was kept below 1.0. In addition, a new technique was used to simultaneously map the free surface deformation. Shadowgraph imaging of the free surface was also used to gain a better understanding of the how. It was found that, depending on the surface condition, the connection of the shedding vortex filaments in the wake of the cylinder was greatly altered with the propensity for surface tension gradients to redirect the vorticity near the free surface to that of the surface-parallel component. This result has an impact on the understanding of turbulent flows in the vicinity of a free surface with varying surface conditions.

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Additional Information:"Reprinted with the permission of Cambridge University Press." Received March 31 1998. Revised August 5 1999. This work has been supported by the Office of Naval Research, ONR-URI grant N00014-94-1-0596 and was performed at GALCIT. The authors would like to thank Professor Thomas Roesgen for his help and insight. In addition, we wish to thank Professor Anthony Leonard for his assistance. The National Science Foundation and Amelia Earhart Fellowship Award also gave financial support to first author Amy Warncke Lang during her graduate studies.
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4196
Deposited By: Tony Diaz
Deposited On:07 Aug 2006
Last Modified:08 Nov 2021 20:15

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