粗糙透水床面明渠水流垂线流速分布的试验研究

冲积河流的粗颗粒河床，具有较大的渗透性，河床渗透对明渠水流运动特性的影响不可忽视．通过水槽试验，研究了河床渗透对垂线流速分布的影响．距试验玻璃水槽进口10m处，设计一个长1．65m、宽0．7m的收缩段，由12层直径1cm的玻璃珠紧密有规则铺成，以模拟粗糙透水床面．其上下游铺上1层相同玻璃珠，形成粗糙度相同但不透水的床面．垂线流速分布通过激光多普勒测速仪及配套的高精度坐标架系统测量．试验施放了3种流量，分别在不透水和透水床面进行垂线流速分布测量．试验结果表明：1）不透水床面的垂线流速分布符合粗糙床面的对数分布公式；2）粗糙透水床面明渠流的垂线流速分布与不透水床面相似；3）相同水流条件下，透水床面的摩阻流速要大于不透水床面；4）透水床面的摩阻流速与积分常数的变化规律有待进一步研究．

Experimental Measurements for the Velocity Distribution of Turbulent Open-channel Flow over a Permeable Rough Bed

A laboratory experimental research is reported, which considered effects of bed permeabili- ty on the velocity distribution of turbulent open-channel flow. The experiment was conducted in a glass-sided flume that was 20 m long, 0.8 m wide and 0. 6 m deep, and its bed was glued a layer of uniform marbles with a diameter of 1 cm. Located at a distance of 10 m from the upstream end of the flume was a rectangular recess that was 1.65 m long and 0. 7 m wide. The permeable bed is simulated in the recess where is well packed with eleven layers of the same marble. The velocity measurements were carried out using a laser Doppler velocimeter （ LDV, DANTEC） and the probe of the LDV was installed by a high resolution traversing system. The measurements were conducted under three flow conditions. Velocity distribution at 2 locations for impermeable bed and 3 for permeable bed were measured. The results show that the velocity distribution for impermeable bed follows the law of the wall when the reference level is lowered to 0. 25-diameter of the marble top. For permeable bed, its distribution is similar to that over impermeable bed, but with larger shear velocity and smaller integra- tion constant. Still, how the shear velocity and integration constant vary need further investigation.