An examination of shear stress partitioning for complex surfaces

Surface roughness aids to ameliorate wind erosion by extracting a portion of the wind's momentum and reducing the quantity of stress on the surface. The goal of this research is to evaluate the effect of different spatial arrangements of surface roughness on the partition of drag forces and distribution of stress at the surface. New drag balance instrumentation was used in a wind tunnel to independently and simultaneously measure the drag on arrays of roughness elements and the drag on the intervening surface. Irwin sensors recorded point measurements of surface shear stress within the arrays. Roughness arrays consisted of film canisters in four different spatial arrangements at four roughness densities.; Results from the tiered force balance and Irwin sensors indicate that the roughness configuration has little impact on the average (R) and maximum (R") drag partition. The protection of the surface increased with roughness density regardless of the roughness arrangement. Point measurements of shear stress revealed that the roughness configuration had a small impact on the distribution of shear stress at the surface, and that a consistent relationship between the maximum and average shear stress existed. Drag partition measurements were compared to the ratios predicted by the Raupach et al. (1993) model and a good degree of agreement was found for all configurations when using a measured values of the beta and m parameter.