粗糙床面风廓线的转折特征及其物理意义  

The Inflected Feature of Wind Profiles over Several Roughness Beds and Its Implications

作　　者：梅凡民[1,2] 江姗姗[1] 王涛[2] 

机构地区：[1]西安工程大学环境与化学工程学院,陕西西安710048 [2]中国科学院寒区旱区环境与工程研究所沙漠与沙漠化重点实验室,甘肃兰州730000

出　　处：《中国沙漠》2010年第2期217-227,共11页Journal of Desert Research

基　　金：国家重点基础研究项目(2006CB403701);陕西省教育厅项目(06JK288);国家自然科学基金项目(40975094)联合资助

摘　　要：为了进一步认识粗糙床面空气动力学粗糙度的物理意义,理解空气动力学粗糙度对动量传递和跃移起动的影响机制,从风洞试验测定的粗糙床面风廓线转折特征入手,分析了粗糙床面的空气动力学性质并提出了内边界层动量传递及近壁区沙粒起动的可能机制。结果表明,细高粗糙元(方向比率在4～20之间)和孔隙粗糙元(孔隙度在0.15～0.75)风廓线呈现4个转折段,对应的湍流垂直分层为近壁区-尾涡层(Z≤0.15H～0.5H)、内边界层-尾涡层过渡层(0.15H≤Z≤0.75H)、内边界层(0.3H～0.75H≤Z≤1.2H～6H)和内边界层与外边界层过渡层等。粗矮粗糙元(粗糙元的方向比率在0.4～1.25之间)风廓线存在几个转折段,对应气流垂直分层为近壁区-尾涡层(Z≤1H～1.5H)和内边界层(1H～1.5H≤Z≤7H～35H)等。细高粗糙元和孔隙粗糙元覆盖21组床面(侧影盖度在0.007～0.50,粗糙元的高度在10～100mm)的内边界层内空气动力学粗糙度在0.07～30.74mm之间,比内边界层以上或以下过渡层的空气动力学粗糙度高几个数量级到数倍;内边界层摩阻风速的0.50～1.66m.s-1之间,是内边界层以下过渡层的1.5～10倍、内边界层以上过渡层的摩阻风速的1.1～2.8倍。内边界层的空气动力学粗糙度和摩阻风速分别代表了粗糙床面对气流阻力特征和湍流切应力。内边界层以下过渡层湍流切应力与粗糙元之间光滑地表所受切应力关系不大,而近壁层切应力与光滑地表所受切应力直接相关。近壁层猝发过程上抛运动和内边界层湍流猝发过程下扫运动耦合关系是内边界层的一部分动量传递到近壁区并导致沙粒起动的可能机制。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·s^-1to 1.66 m·s^-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.

关 键 词：风廓线 空气动力学粗糙度 摩阻风速 湍流猝发 跃移 

分 类 号：X169[环境科学与工程—环境科学]