基于LSIBM-LES的浅水河岸水轮机尾流特性分析

Wake characteristic of shallow channel streambank hydrokinetic turbine based on LSIBM and LES

设计了一种部分嵌入在浅水河岸侧壁上的新型阻力型垂直轴水轮机.这种水轮机在河流中层运行,可以有效适应流量、泥沙等多种环境因素的变化,且对鱼类等水生生物友好.为研究水轮机的性能及尾流特性,对其在明渠中的流动过程进行了大涡模拟(LES).采用基于水平集函数的浸入边界法(LSIBM)分别描述了规则半圆柱形空腔及复杂水轮机的几何结构,并基于耦合水平集流体体积(CLSVOF)法捕捉不断变化的自由液面.将计算得到的不同叶尖速比下的水轮机功率系数与模型试验结果进行对比,验证了数值仿真结果的准确性.基于计算结果对雷诺应力进行了三重分解,结果显示水轮机近尾流区域的不稳定性与叶片通过频率密切相关.

A new drag-type vertical axis hydrokinetic turbine,partially embedded in a relatively shallow channel streambank,was designed and studied. The turbine was designed operate at river mid-depth,which can effectively adapt to the varying flow discharge,sediment transport in the small-sized to medium-sized open channel flows and be friendly to fish and aquatic creatures.To study its performance and wake characteristics,large-eddy simulation of the turbine in an open channel flow was carried out.The turbine system′s geometry,including the regular semi-cylindrical cavity along the bank and the complex rotor,was captured by the LS-based immersed boundary method. Coupled level-set and volume-of-fluid method was used to capture the deformable free surface.The power coefficients of the turbine at different tip speed ratios were calculated and compared against results obtained in the experiment,to validate the accuracy of the simulation results. It can be found that the unsteadiness in the near wake of the turbine is strongly associated with the blade passing frequency by applying a triple decomposition on the Reynolds stresses.