Journal of Fluid Mechanics



Comparison between rough- and smooth-wall turbulent boundary layers


P.-å.  Krogstad a1, R. A.  Antonia a2 and L. W. B.  Browne a2
a1 Division of Hydro- and Gas Dynamics, Norwegian Institute of Technology, Trondheim, 7034, Norway
a2 Department of Mechanical Engineering, University of Newcastle, NSW 2308, Australia

Article author query
krogstad p   [Google Scholar] 
antonia ra   [Google Scholar] 
browne lw   [Google Scholar] 
 

Abstract

Measurements in a zero-pressure-gradient turbulent boundary layer over a mesh-screen rough wall indicate several differences, in both inner and outer regions, in comparison to a smooth-wall boundary layer. The mean velocity distribution indicates that, apart from the expected k-type roughness function shift in the inner region, the strength of the rough-wall outer region ‘wake’ is larger than on a smooth wall. Normalizing on the wall shear stress, there is a significant increase in the normal turbulence intensity and a moderate increase in the Reynolds shear stress over the rough wall. The longitudinal turbulence intensity distribution is essentially the same for both surfaces. Normalized contributions to the Reynolds shear stress from the second (Q2) and fourth (Q4) quadrants are greater over the rough wall. The data indicate that not only are Q2 and Q4 events stronger on the rough wall but their frequency of occurrence is nearly twice as large for the rough wall as for the smooth wall. Comparison between smooth- and rough-wall spectra of the normal velocity fluctuation suggests that the strength of the active motion may depend on the nature of the surface.

(Published Online April 26 2006)
(Received June 7 1991)
(Revised April 1 1992)



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