侧式进/出水口偏流出流下的大涡模拟

Study on large eddy simulation of lateral inlet/outlet under bending outflow

实际工程中受地形地质条件影响,引水洞在水平上存在转角,导致出流工况来流不均,进/出水口内部紊流特性的复杂程度显著提升。利用大涡模拟对某带水平弯段抽水蓄能电站侧式进/出水口进行数值计算,其流速、概率密度分布与模型试验吻合较好。结果表明:偏流出流下进/出水口各流道分流比分别为0.64、0.81、1.26和1.29,水平方向流速分布极为不均;垂直方向主流靠近中下部,垂向雷诺切应力在扩散段内呈一正一负峰值分布,该现象主要由中上部的流动分离和底部的壁面剪切造成;两中间流道的回流区高度大于两边流道,导致中间流道的拦污栅更易受到反向流速影响;流动分离使拦污栅附近存在三轴漩滚,靠近过水断面中上部和底部产生2处能量集中的低频脉动,且各流道在偏流条件下的紊动强度相比均匀来流的紊动强度分别提高11%、25%、29%、3%,不利的水流流态和较高的紊动强度可能对拦污栅造成威胁。

Due to the influence of topography and geology in actual engineering projects,water tunnels often have horizontal bends.These bends result in non-uniform inflow conditions,complicating the turbulence characteristics at the inlet and outlet compared to straight-line tunnels.This study employs Large Eddy Simulation to analyze a real engineering problem.The calculated results are compared with experimental data,revealing close agreement in flow velocity and probability density distribution.The findings show that under outflow conditions,the flow-split ratios for each channel are 0.64,0.81,1.26,and 1.29,indicating a highly non-uniform horizontal velocity distribution.In the vertical direction,the main flow occurred primarily in the lower middle section,and the vertical Reynolds shear stress in the diffusion segment exhibits a distinctive pattern with alternating positive and negative peaks.This phenomenon is primarily attributed to flow separation in the upper middle area and wall shearing near the bottom.The recirculation region′s height in the two middle channels was found to be greater than that in the side channels,indicating that trash racks in the central channels are more susceptible to reverse flow velocities.Additionally,flow separation near the trash rack gives rise to a three-axis vortex,while two energy-concentrated pulsations occur in the upper middle section and near the bottom.Moreover,under bending flow conditions,turbulence intensities in different channels increase by 11%,25%,29%,and 3%,respectively,compared to those in uniform flow situations.Consequently,the unfavorable flow regime and high turbulence intensity associated with bending flow pose a threat to the trash rack.