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An experimental investigation of coherent substructures associated with turbulent spots in a laminar boundary layer

Published online by Cambridge University Press:  20 April 2006

Eric C. Itsweire  and
Charles W. Van Atta
Eric C. Itsweire
Affiliation:
Department of Applied Mechanics and Engineering Sciences, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093
Charles W. Van Atta
Affiliation:
Department of Applied Mechanics and Engineering Sciences, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093
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Abstract

Longitudinal and transverse components of the velocity were simultaneously measured for various vertical locations at 20 off-centreline positions in turbulent spots artificially generated in a zero-pressure-gradient laminar boundary layer. Global ensemble-averaged velocity diagrams and vertical vorticity contours were computed in similarity coordinates ξ = (x − x0)/(U∞(t−t0)) and ζ = z/(U∞(t−t0)) for different heights η = y/δ* above the plate. This global averaging technique inadequately describes the spot, which is not a single large vortex structure. A discriminative averaging technique was developed to construct a ‘statistically most-probable’ spot with sufficient resolution to include some of the largest substructures detected in visual studies. Four eddies were identified in vertical slices of the central region of the spot, while several rows appeared in the plan view. These features of the velocity and vorticity contours of the statistically most-probable spot exhibit similarities with structures observed in flow visualizations.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 148 , November 1984 , pp. 319 - 348
Copyright
© 1984 Cambridge University Press

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