关键词: 总阻力系数, 直立植被阻力系数, 粗糙度, 风洞试验

Abstract: Using cylindrical wooden sticks of varying density and height to model standing vegetation, detailed wind velocity distributions were measured above the vegetated surface in wind tunnel. The overall drag coefficient and roughness length were derived by a curve-fitting method. Both the height and density of standing vegetation influenced the drag coefficient and roughness length, but their relative importance was different. Standing vegetation is used to protect the soil prone to wind erosion, because the total drag partitions between the standing vegetation and the intervening surface, expressed as: τ=F_r/S+τ_s·S'/S. Due to the disturbance of the vegetated surface, the shearing stress at the intervening surface is decreased and the soil becomes difficult to be driven by wind. So it is necessary to determine the drag force on standing vegetation. However, the direct measurement is very difficult. This study here focused on calculating the standing vegetation drag coefficient according to C_D=2u_*²/u_z²=C_fL_c when lateral cover L_c≥0.03,τ_s is negligible. The results reached are that C_f varies linearly with 1/L_c but is largely independent of AR. Good correlation existed between the derived roughness length and overall drag coefficient implies that it is reliable to obtain the overall drag coefficient and roughness length by curve-fitting method so long as caution is taken in selecting the appropriate measurements.

Key words: overall drag coefficient, standing vegetation drag coefficient, roughness length, wind tunnel test