陡坡粗糙矩形明渠中自由跌流的水力特性

Hydraulic Characteristics of Free Overfall in a Steep and Rough Rectangular Channel

在矩形明渠中,自由跌水可作为其流量计量设施,具有简单方便、运行维护容易的特点。工程中,矩形明渠底坡往往为陡坡,边壁因材料限制通常较粗糙,体现为陡坡粗糙渠道的特征。目前对此类明渠中设置跌坎后,跌坎上的水力特征性研究较少。本文采用模型试验的方法对不同底坡S、不同边壁粗糙度n的矩形明渠中的自由跌水水力特性进行了研究。试验中,底坡范围为0.0026到0.0973之间,明渠边壁糙率系数在0.0093到0.0193之间,明渠水流弗洛德数Fr0在1.0到6.62之间,远超以前研究的范围。结果表明:在试验确定的底坡和边壁糙率系数范围内,明渠跌坎上游水流为急流,自由跌流坎末水深he与其上游临界水深hc之比值he/hc与√S/n呈线性相关。另外,受自由跌水影响的跌坎上游长度L只与底坡和边壁糙率系数有关,而与渠道流量无关。对陡坡渠道而言,he/hc值随着水流弗洛德数的增加而呈对数减小。最后本文根据试验数据提出了陡坡粗糙矩形明渠的自由跌流坎末水深与上游临界水深之比值he/hc和√S/n,L和√S/n以及he/hc和来流弗洛德数Fr0的计算公式。本文通过增大底坡和边壁糙率的值,进一步扩展了前人关于明渠自由跌水的研究,这对于利用明渠自由跌水进行流量计量具有重要的工程应用价值。

In the rectangular open channel,the free overfall can be used as the discharge measure device.In the channel project,the channel usually has the features as a rough and steep one.Few study is conducted on the hydraulic characteristics of free overfall in a rough and steep rectangular channel.An experimental study of the free overfall from a rectangular channel with differing slopes and wall roughness were investigated in this paper.In the tests,the bed slope S ranged from 0.0026 to 0.0973,the wall Manning roughness coefficient n ranged from 0.0093 to 0.0193,and the flow Froude number Fr0 ranged from 1.0 to 6.62,which were much wider than previous studies.The results showed that,when the flow of upstream at the end was supercritical,the ratio of the end-depth he and critical-depth hc(he/hc)was linearly related to√S/n in a wider range of theslope and the wall Manning roughness coefficient.In addition,the length of upstream flow influenced by overfall L was only related to the bed slope and the wall Manning roughness coefficient.For the channels with steep slope,he/hc decreased with the increase of logarithm of the flowFroude number Fr0.Using the experimental data,the formulas of he/hc and√S/n,L and√S/n and he/hc and Fr0,were proposed in the rough andsteep rectangular channel with a free overfall.This study expanded the range of the bed slope and the wall Manning roughness coefficient,which was important to the application of free overfall when used as a discharge measure device.