不同交汇角度明渠交汇口三维水力特性的大涡模拟研究

Three-dimensional numerical study of hydraulic characteristics at open-channel junctions with different intersection angles by Large Eddy Simulation

采用气液两相流混合模型对不同交汇角度下等宽明渠交汇口三维水力特性进行了数值模拟研究。选取大涡模型(Large Eddy Model)封闭两相流时均方程,求解速度与压力耦合方程组时使用半隐式SIMPLE(Semi-Implicit Method for Pressure-Linked Equations)算法,模拟自由水面采用VOF(Volume of Fluid)法。将交汇角度为90°时采用大涡模型计算得到的纵向截面水面线和不同测线上的速度分布与文献中的试验结果相比较,两者吻合良好,且水面线高度误差在4.2%以内,由此可见大涡模型是模拟交汇口水力特性的有效方法。进而将大涡模型用于模拟交汇角度为30°、45°、60°的交汇口水流,得到交汇口处的水深变化及流场的分布规律,并定量分析了交汇口下游各横断面流速不均匀系数的分布规律。结果表明:在整体上交汇角度越大,交汇口各特征横断面流速不均匀系数越大,即水流流速分布越不均匀。

The gas-liquid two-phase mixture model is used to numerically compute the hydraulic characteristics of open-channel junction flows at different intersection angles. The large eddy model（LES） is used to close the two-phase time-averaged equations; the SIMPLE（Semi-Implicit Method for Pressure-Linked Equations） algorithm is used to solve velocity and pressure coupling equations; and simulation of free surface is done by the VOF（Volume of Fluid） method. Comparisons of the computed water surface and velocity distribution along different vertical lines of 90° open-channel junction with the experimental data in the literature show that they are in good agreement and the water surface error is less than 4.2%,which shows that the large eddy modelis an effective way to study the 3D hydraulic characteristics of open junctions. Therefore, the large eddy model is further used to simulate the hydraulic characteristics of 30°、45°、60°open-channel junctions, and the water surface and velocity distribution are obtained. And the quantitative analyses of the flow velocity non-uniform coefficient distribution of the various cross-sections downstream junction show that the greater the non-uniform coefficient becomes, the more uneven the distribution of flow velocity becomes with an increase of a junction angleof the overall.