Viscous drag reduction on a submerged surface can be obtained both in the limit of an unbroken gas film coating the solid and in the nanobubble or perhaps microbubble coating regime when an air layer is created with superhydrophobic coatings. We examine an intermediate bubble size regime with a trapped-bubble array (TBA) formed in a tap water environment using electrolysis to grow and maintain bubbles in thousands of millimeter-sized holes on a solid surface. We show that even though surface tension is sufficient to stabilize bubbles in a TBA against hydrostatic and shear forces beneath a turbulent boundary layer, no drag reduction is obtained. Drag measurements were acquired over Reynolds numbers based on plate length ranging from using either a force balance for plates mounted in a vertical orientation, or by performing a momentum integral balance using a wake survey for a flat plate mounted in either vertical or horizontal orientation. In that the drag forces were small, emphasis was placed on minimizing experimental uncertainty. For comparison, the flow over a flat plate covered on one side by a large uninterrupted gas film was examined and found to produce large drag reductions of up to 32%.
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e-mail: kelly.stephani@mail.utexas.edu
e-mail: david@cfdlab.ae.utexas.edu
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April 2010
Research Papers
An Examination of Trapped Bubbles for Viscous Drag Reduction on Submerged Surfaces
Kelly A. Stephani,
Kelly A. Stephani
Department of Aerospace Engineering and Engineering Mechanics,
e-mail: kelly.stephani@mail.utexas.edu
University of Texas at Austin
, 1 University Station, C0600 Austin, TX 78712-0235
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David B. Goldstein
David B. Goldstein
Department of Aerospace Engineering and Engineering Mechanics,
e-mail: david@cfdlab.ae.utexas.edu
University of Texas at Austin
, 1 University Station, C0600 Austin, TX 78712-0235
Search for other works by this author on:
Kelly A. Stephani
Department of Aerospace Engineering and Engineering Mechanics,
University of Texas at Austin
, 1 University Station, C0600 Austin, TX 78712-0235e-mail: kelly.stephani@mail.utexas.edu
David B. Goldstein
Department of Aerospace Engineering and Engineering Mechanics,
University of Texas at Austin
, 1 University Station, C0600 Austin, TX 78712-0235e-mail: david@cfdlab.ae.utexas.edu
J. Fluids Eng. Apr 2010, 132(4): 041303 (9 pages)
Published Online: April 20, 2010
Article history
Received:
June 27, 2008
Revised:
February 9, 2010
Online:
April 20, 2010
Published:
April 20, 2010
Citation
Stephani, K. A., and Goldstein, D. B. (April 20, 2010). "An Examination of Trapped Bubbles for Viscous Drag Reduction on Submerged Surfaces." ASME. J. Fluids Eng. April 2010; 132(4): 041303. https://doi.org/10.1115/1.4001273
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