凸底明渠流速分布试验研究

Experimental study on velocity distribution in open channel with a bottom sill

通过对三角形和梯形凸底存在下明渠中垂线处流速分布的试验研究和理论分析,建立了流速抛物线型垂向分布公式,发现抛物线待定系数和凸底迎水坡度存在线性关系;随着凸底迎水坡度的增加,无量纲最大流速的位置逐渐下降,最低甚至达到0.41,偏离水面较远;最大流速随流量增加而增大,而最大流速与断面平均流速之比接近为常数。本文公式计算的流速分布与水槽试验资料颇为一致,表明公式能较好地反映凸底明渠中垂线处的流速分布特点,且流速越小,公式精度越高。

A laboratory experiment, along with theoretical analysis, was conducted to study the vertical profiles of flow velocity on the center plane of an open channel with a bottom sill, and from the measurements a parabolic formula was established for the profiles at the crest of sills with different shapes. Results show a linear relationship of the parabola coefficient versus the slope of the upstream sill face. And, the peak of the velocity profiles moves closer to the channel bottom as this sill slope increases, with its lowest position at a bottom distance as small as 41% of the flow depth, i.e. far away from the water surface. The peak value of velocity is increased with the increasing flow rate, but the ratio of peak to mean velocity approaches to constant. Calculations of this formula agree with the measurements and its accuracy is higher for lower velocity, showing it effective in description of the actual velocity over the sills.