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The effects of surface topography on momentum and mass transfer in a turbulent boundary layer

Published online by Cambridge University Press:  20 April 2006

R. A. Dawkins  and
D. R. Davies
R. A. Dawkins
Affiliation:
Department of Mathematics, University of Exeter, U.K. Present address: British Aerospace, Kingston-upon-Thames, U.K.
D. R. Davies
Affiliation:
Department of Mathematics, University of Exeter, U.K.
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Abstract

An approximate, conveniently applied theory with corresponding experimental data is presented concerning the changes in momentum and mass transfer produced by a ridge of small slopes in a flat-surface quasi-stationary turbulent boundary layer. A first-order mean velocity perturbation solution is found to be in good agreement with measured velocities on the up-slope side of a two-dimensional ridge, of length 20 cm and height 1 cm, fixed on the floor of the working section of an open-circuit wind tunnel. A vapour-transfer eddy-diffusivity distribution is then calculated for the inner boundary-layer region and solutions of the consequent vapour-transfer equation give the variation of rate of evaporation from surfaces of varying lengths placed at different positions on the up-slope region of the ridge. Corresponding measurements are found to be in good agreement with the theoretical calculations, and show that, even over small slopes (of 1 in 10), the evaporation rate varied with position by 25% from maximum to minimum. This method of calculation is extended to examine the effect of surface curvature on diffusion of gas from an upstream line source in a turbulent boundary layer over the ridge; experimental and theoretical concentration profiles compare extremely well over the leading slope.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 108 , July 1981 , pp. 423 - 442
Copyright
© 1981 Cambridge University Press

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