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The accelerated fully rough turbulent boundary layer

Published online by Cambridge University Press:  12 April 2006

Hugh W. Coleman ,
Robert J. Moffat  and
William M. Kays
Hugh W. Coleman
Affiliation:
Sandia Laboratories, Livermore, California 94550
Robert J. Moffat
Affiliation:
Department of Mechanical Engineering, Stanford University, Stanford, California 94305
William M. Kays
Affiliation:
Department of Mechanical Engineering, Stanford University, Stanford, California 94305
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Abstract

The behaviour of a fully rough turbulent boundary layer subjected to favourable pressure gradients both with and without blowing was investigated experimentally using a porous test surface composed of densely packed spheres of uniform size. Measurements of profiles of mean velocity and the components of the Reynolds-stress tensor are reported for both unblown and blown layers. Skin-friction coefficients were determined from measurements of the Reynolds shear stress and mean velocity.

An appropriate acceleration parameter Kr for fully rough layers is defined which is dependent on a characteristic roughness dimension but independent of molecular viscosity. For a constant blowing fraction F greater than or equal to zero, the fully rough turbulent boundary layer reaches an equilibrium state when Kr is held constant. Profiles of the mean velocity and the components of the Reynolds-stress tensor are then similar in the flow direction and the skin-friction coefficient, momentum thickness, boundary-layer shape factor and the Clauser shape factor and pressure-gradient parameter all become constant.

Acceleration of a fully rough layer decreases the normalized turbulent kinetic energy and makes the turbulence field much less isotropic in the inner region (for F equal to zero) compared with zero-pressure-gradient fully rough layers. The values of the Reynolds-shear-stress correlation coefficients, however, are unaffected by acceleration or blowing and are identical with values previously reported for smooth-wall and zero-pressure-gradient rough-wall flows. Increasing values of the roughness Reynolds number with acceleration indicate that the fully rough layer does not tend towards the transitionally rough or smooth-wall state when accelerated.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 82 , Issue 3 , 27 September 1977 , pp. 507 - 528
Copyright
© 1977 Cambridge University Press

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