Wind velocity profiles with a blowing sand boundary layer: Theoretical simulation and experimental validation

Physics

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Atmospheric Processes: Boundary Layer Processes, Geodesy And Gravity: Ocean/Earth/Atmosphere/Hydrosphere/Cryosphere Interactions (0762, 1218, 3319, 4550), Atmospheric Processes: Land/Atmosphere Interactions (1218, 1631, 1843), Planetary Sciences: Solid Surface Planets: Erosion And Weathering

Scientific paper

Describing wind velocity profiles modified by the movement of blown sand is of continuing significance because they are thought to bear rich information about wind-sand interaction in a blowing sand cloud. This paper treats the saltating cloud as a fluidized particle flow and develops a mathematical model of the wind-sand interactions. The force exerted on the air by saltating particles is characterized by introducing a drag coefficient of the fluidized aeolian particle flow that is modified after the drag coefficients proposed for liquid fluidized particle flow. The resulting model was then used to simulate wind velocity profiles in the presence of a saltation cloud on the basis of the mean particle velocity and particle concentration profiles of the fluidized particle flow obtained from wind tunnel tests. The simulated velocity profiles agree well with those directly measured in the wind tunnel. The blowing sand boundary layer is divided into a saltation subboundary layer, in which saltating particles participate in momentum exchange with the wind, and an outer subboundary layer above the saltation subboundary layer. The wind velocity profiles within the saltation subboundary layer are characterized by convex-upward curves in a log (height)-linear (wind velocity) plot rather than the straight lines in the velocity profiles of clean wind. The upward convexity of the velocity profiles increases as wind velocity increases, suggesting that more wind momentum is absorbed by the saltating particles as the sand transport rate increases. The wind velocity profiles in the outer subboundary layer approach the Prandtl logarithmic law with the saltation subboundary layer providing increased aerodynamic roughness. Our results suggest that the wind shear velocity in the presence of a saltation cloud is a physical dimension that can reflect the effect of saltation.

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