A wind tunnel investigation of roughness properties over non-homogeneous rough surfaces
✍ Scribed by Fumi Sugita; Tokuo Kishii; Yasuhisa Kuzuha; Tsutomu Yamanaka
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 266 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0885-6087
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✦ Synopsis
Laboratory experiments were conducted to study the properties of roughness parameters over surfaces with small-scale heterogeneity, using a wind tunnel ®tted with an underlying weighting lysimeter packed with uniform ®ne 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 ®tting the ¯ux pro®le equations to the mean pro®les observed. The ¯ow over a non-homogeneous rough surface was observed to become homogeneous above a certain height, so that eective' parameters can be found to describe the average surface ¯uxes from the non-homogeneous surface. The roughness properties of the non-homogeneous surfaces are, in general, similar to those of homogeneous surfaces. The eective' parameter values, however, suggest that the surface non-homogeneity which is a perturbation part of the obstacle distribution has a signi®cant eect on roughness properties, and that the `eective' 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 signi®cantly 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.