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RESEARCH PAPERS

Heat Transfer Visualization and Measurement in Unstable Concave-Wall Laminar Boundary Layers

[+] Author and Article Information
R. I. Crane, J. Sabzvari

Department of Mechanical Engineering, Imperial College of Science & Technology, London, SW7 2BX, United Kingdom

J. Turbomach 111(1), 51-56 (Jan 01, 1989) (6 pages) doi:10.1115/1.3262236 History: Received February 11, 1988; Online November 09, 2009

Abstract

Using liquid crystal sheet in a hybrid constant-wall-temperature/constant-heat-flux procedure, heat transfer distributions have been measured in concave-wall laminar boundary layers with a natural Gortler vortex system in a near-zero pressure gradient. Stanton numbers at vortex downwash positions across the span exceeded those at upwash positions by factors as high as three. Spanwise-averaged Stanton numbers exceeded analytical flat-plate values only after the appearance of highly inflected upwash velocity profiles and the onset of span wise meandering of the vortices, where the Gortler number exceeded ten. Levels then reached values comparable with turbulent correlations, at Reynolds numbers and turbulence levels (up to 3 percent) where previous measurements of the intermittency factor indicated that transition had not begun. Boundary layer thinning in downwash zones could account for much of the heat transfer enhancement. The phenomenon could be a contributory factor to the long, apparently transitional regions often reported on blade cascade pressure surfaces, although the Gortler numbers where enhancement occurred are higher than those normally associated with pressure-surface transition.

Copyright © 1989 by ASME
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