固定沙质床面的空气动力学粗糙度

Aerodynamic Roughness of Fixed Sandy Beds

通过固定沙质床面的空气动力学粗糙度z0的风洞实验研究,结果表明,z0与沙粒粒径的关系为:z0=a1+b1D2ln(D),并非Bagnold的1/30定律,也不是其他研究者的z0与沙粒粒径D的固定关系。Bagnold的1/30定律仅对有限风速情况和非常狭窄的颗粒粒径范围有效。风也是影响空气动力学粗糙度的活跃因子。z0与沙粒粒径,z0与摩阻速度,z0与摩阻雷诺数之间的关系都与风速有关。类似于水利学粗糙度,将空气动力学粗糙度划分为空气动力学完全光滑区、过渡区和完全粗糙区三个区域。

We report here the wind tunnel results of systematic tests of the aerodynamic roughness lengths of different sized fixed sand beds at different free\|stream wind velocities. The results suggest that there are complex variations of aerodynamic roughness length. Wind is an active factor in determining the aerodynamic roughness length of fixed sand beds. The so\|called 1/30 law in aeolian research proposed by Bagnold more than a half\|century ago for sand surfaces is found to suffer some limitations. Some multivariate models relating aerodynamic roughness length and other factors are provided. The similarities between aerodynamic roughness and hydraulic roughness are compared. Aerodynamic roughness is divided into aerodynamically smooth, transitional and completely rough regimes.