Journal of Fluid Mechanics



Structure of turbulent boundary layers on smooth and rough walls


P.-Å.  Krogstad a1 and R. A.  Antonia a2
a1 Division of Mechanics, Thermo- and Fluid Dynamics, Norwegian Institute of Technology, N-7034 Trondheim, Norway
a2 Department of Mechanical Engineering, University of Newcastle, NSW, 2308, Australia

Article author query
krogstad p-Å   [Google Scholar] 
antonia ra   [Google Scholar] 
 

Abstract

The structure of turbulent boundary layers which develop with zero pressure gradient on a smooth wall and a k-type rough wall was examined using arrays of X-wires. Although the data were obtained only on two orthogonal planes, the technique provides some information on the three-dimensionality of the large-scale structures. The major effect of the roughness is to tilt the inclination of the structures towards the wall-normal direction. This is caused by the reduced damping of the wall-normal velocity fluctuations close to the rough surface and the break-up of structures whose scales are comparable to the size of the roughness elements. Both effects cause a reduction in the streamwise lengthscales, as suggested by all the measured two-point correlations. The correlations also show that the roughness tends to reduce the overall anisotropy of the large-scale motion. There is evidence to suggest that the magnitude of the vorticity field is larger over the rough wall.

(Published Online April 26 2006)
(Received September 6 1993)
(Revised March 28 1994)



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