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A wind tunnel investigation of roughness properties over non‐homogeneous rough surfaces
Author(s) -
Sugita Fumi,
Kishii Tokuo,
Kuzuha Yasuhisa,
Yamanaka Tsutomu
Publication year - 1998
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/(sici)1099-1085(19981030)12:13/14<2149::aid-hyp726>3.0.co;2-l
Subject(s) - surface roughness , surface finish , homogeneous , roughness length , homogeneity (statistics) , materials science , wind tunnel , isotropy , mechanics , geometry , optics , meteorology , composite material , mathematics , physics , wind speed , thermodynamics , wind profile power law , statistics
Laboratory experiments were conducted to study the properties of roughness parameters over surfaces with small‐scale heterogeneity, using a wind tunnel fitted with an underlying weighting lysimeter packed with uniform fine sand. Either small columns or sand ridges were distributed homogeneously or non‐homogeneously on the surface as roughness obstacles. The roughness lengths for momentum ( z 0m ), heat ( z 0h ) and vapour ( z 0v ) were estimated for each surface by fitting the flux profile equations to the mean profiles observed. The flow over a non‐homogeneous rough surface was observed to become homogeneous above a certain height, so that ‘effective’ parameters can be found to describe the average surface fluxes from the non‐homogeneous surface. The roughness properties of the non‐homogeneous surfaces are, in general, similar to those of homogeneous surfaces. The ‘effective’ parameter values, however, suggest that the surface non‐homogeneity which is a perturbation part of the obstacle distribution has a significant effect on roughness properties, and that the ‘effective’ roughness of a non‐homogeneous surface is always considerably greater than the actual average roughness. The values of z 0m for the non‐homogeneous surfaces are significantly greater than scalar roughness lengths ( z 0h and z 0v ). Though homogeneous rough surfaces also have z 0m / z 0m and z 0m / z 0v ) ratios of greater than unity, these ratio values for non‐homogeneous surfaces are found to be almost one order of magnitude greater than those for homogeneous surfaces, even when the homogeneous and the non‐homogeneous surfaces have the same average roughness. Copyright © 1998 John Wiley & Sons, Ltd.