河道中受侧壁影响的断面流速分布规律研究

Study on cross sectional velocity distribution affected by sidewall in river channel

断面水流流速分布是研究河道水流泥沙运动规律的基础。天然河流断面形态不同,其流速分布特性也有差别:对于比较宽浅的河道,侧壁对断面流速分布的影响较小,流速沿垂线分布梯度较大,垂线上最大流速一般位于水面,垂线平均流速沿河宽方向(横向)分布较均匀;对于较窄深的河道,侧壁对流速分布的影响较大,流速沿垂线分布较均匀,垂线上最大流速一般位于水面以下,垂线平均流速沿河宽分布梯度较大,因此,对于较窄深的河道必须考虑侧壁对流速分布的影响。本文在分析天然河道流速分布特性的基础上,从紊流的雷诺方程出发,推导获得了水流受侧壁影响的横断面流速分布公式和垂线平均流速沿河宽分布的公式。公式计算结果与水槽试验和天然河流实测流速分布资料的比较分析表明,公式能较好地反映流速沿垂线和沿横向的分布特性,具有较好的理论和实用价值。

Water velocity distribution in a cross section of open channel is a basis for the research of wa- ter and sediment movement. The velocity distribution of natural rivers is not always the same because of the different shapes of cross sections. For the relatively wide-shallow river, there is a less effect of side- wall on the velocity distribution within cross section and the vertical velocity gradient is relatively larger with the maximum velocity on the water surface and the average vertical velocity along the river width （hori- zontal direction） is uniform. For the narrow-deep river, there is a larger effect of sidewall on the velocity distribution which is relatively uniform in vertical with the maximum velocity always happened to beneath the water surface and with a larger gradient of the average vertical velocity along the river width direction. Therefore, for narrow-deep rivers, the sidewall influence on velocity distribution must be considered. Based on the velocity distribution analysis of natural rivers, the cross sectional and average vertical velocity distri- bution formula affected by sidewall have been derived in this paper from the Reynolds equation of turbulent flow. The comparisons between calculated results of the derived formula and measured data of flume experi- ment and natural rivers show that the agreement is good.