密排粗糙床面明渠水流的流速结构

Velocity Structure of Open Channel Flow with Dense Roughness

密排粗糙床面在江河治理工程措施中应用广泛,采用不同直径d的圆形玻璃珠制作了3种密排加糙床面,基于光滑床面和密排加糙床面的8组PIV水槽明渠均匀紊流试验资料,研究床面粗糙对明渠水流流速结构的影响规律。结果表明,密排加糙床面明渠紊流的理论床面位置约在颗粒顶部以下0.15d处;粘性底层以外区域的纵向时均流速垂线分布满足对数公式,卡门常数κ=0.4,积分常数A=9.6~11.8,且A随粗糙雷诺数Re_*呈幂函数递增变化;床面加糙对内区流速的影响大于外区。脉动流速u、v的空间自相关系数C_(uu)、C_(vv)为正值,空间互相关系数C_(uv)、C_(vu)为负值,C_(uu)云图分布大体呈水平略向上倾斜的椭圆形,C_(vv)云图分布大致呈圆形,C_(uv)、C_(vu)的云图分布总体均呈第2、4象限倾斜的椭圆。流量Q增大后,C_(uu)分布椭圆形状变得细长,C_(vv)分布与圆形更为接近,C_(uv)、C_(vu)分布椭圆长轴与水平轴的倾角均减小;床面加糙对C_(uu)影响较小,而对C_(vv)、C_(uv)、C_(vu)的影响较大,加糙后C_(vv)、C_(uv)、C_(vu)绝对值总体减小,空间相关性减弱。

Dense bed roughness is widely used in river governance engineering measures.Three kinds of dense roughness beds were made by round glass beads with different diameter d.Based on eight sets of instantaneous velocity data investigated by Particle Image Velocimetry（PIV）measurements in longitudinal sections for open-channel flows over smooth and rough beds,the influence of bed roughness on the velocity structure of open channel flow were studied.The results show that the theoretical bed location of open channel turbulence with dense roughness beds is about 0.15dbelow the top of the beads.Vertical distribution of longitudinal mean velocity in the region outside the viscous sublayer satisfies the logarithmic formula,with the Karman constantκ=0.4and the integral constant A=9.6-11.8.Furthermore,Aincreases in apower function with the roughness Reynolds number Re_＊.The influence of bed roughness on the longitudinal mean velocity in the inner region is greater than that of the outer region.The spatial autocorrelation coefficient of fluctuating velocity Cuuand Cvvis positive,and the spatial intercorrelation coefficient Cuvand Cvuis negative.The cloud chart distribution of Cuuis generally elliptical horizontally slightly upward,and the cloud chart distribution of Cvvis roughly round,while the overall distribution of Cuvand Cvuare second,fourth quadrant ellipses.With the increase of flowQ,the distributed ellipse of Cuu becomes slender,the distribution of Cvvis closer to the circle,and the inclination angles between the long axis and horizontal axis of the distribution ellipse of Cuvand Cvuare both reduced.Bed roughness has little impact on Cuu,but it has a greater impact on Cvv,Cuv,and Cvu.The absolute value of Cvv,Cuv,and Cvudecreases with the increase of bed roughness,which means the spatial correlation is weakened.