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Shear
Stress Behaviour on Complex Rough Surfaces
J.A. Gillies and W.G. Nickling
Abstract
A newly developed drag plate was used in a wind tunnel to examine the behaviour of
surface shear stress generated by fully developed turbulent boundary flow. Three different
complex rough gravel surface configurations were tested. Roughness was measured with a
laser profiling system. The measured surface shear stress (s) obtained
with a newly designed drag plate was found to scale in proportion to the shear stress (0)
determined from wind profile measurements using Pitot tubes, as a function of increasing
surface roughness. In addition, increased surface roughness caused increased variability
in s as quantified by the standard deviation which scaled as a
function of boundary Reynolds number (Reb). It was also noted that the
distribution of measured surface shearing stress changed with increasing roughness. The s
data showed different responses for each of the surface roughness configurations to
similar ranges of wind profile measured shear stress. As roughness increased, s
increased, due to the creation of more energetic turbulent activity, increased wall
bursting, and increased bluff body effects caused by the elements protruding higher into
the boundary layer flow. |
