| 沙漠与沙漠化 |
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| The Inflected Feature of Wind Profiles over Several Roughness Beds and Its Implications |
| MEI Fan-min1,2, JIANG Shan-shan1, WANG Tao2 |
| 1.School of Environmental and Chemical Engineering, Xian Polytechnic University, Xian 710048, China; 2.Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China |
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Abstract To further understand physical significance of aerodynamic roughness length, vertical structure of turbulence and saltation threshold mechanism are analyzed on basis of inflected feature of wind profiles over roughness beds in wind tunnel. For the wind profiles over these beds covered with slender elements (aspect ratio of individual element, AR,4~20) and porous elements (geometric porosity, 0.15~0.75) respectively, they all exist four inflected region, which can be interpreted as near wall-wake layer (Z≤0.15~0.5H), transition region (0.15H≤Z≤ 0.75H), inner layer (0.3~0.75H≤Z≤1.2~6H) and transition layer between inner and outer layer. The wind profiles over those beds with dumpy elements (AR,0.4~1.25) also have several inflections that can be classified into near wall-wake layer (Z≤1~1.5H) and inner layer (0~1.5H≤Z≤7~35H). Aerodynamic roughness lengths of inner layers over the beds with the slender and porous elements range from 0.07 mm to 30.74 mm, which are higher several times or orders of magnitude than those of transition layers. Correspondingly, wind friction velocities of inner layers over those beds, ranging from 0.50 m\5s-1to 1.66 m\5s-1, are 1.5~10 times than those of the bottom transition layers and are 1.1~2.8 times than those of the top transition layers. The aerodynamic roughness lengths and wind friction velocities of inner layers reflect aerodynamic property and overall shear stress over the roughness beds. The near wall shear stress could be more related to local shear stress of smooth surface between roughness elements than that of the bottom transition layers. The coupling between ejection event of near wall and sweep event of inner layer could transmit some momentum of inner layer into near wall and cause sand particles to be entrained into air. The hypothesis should be verified in the future by wind tunnel experiment.
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Received: 27 July 2008
Published: 20 March 2010
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2010, Vol. 30 
