水轮机全三维粘性大涡模拟数学模型研究

采用大涡模拟技术,建立了绝对坐标系和相对坐标系下的联合计算数学模型,控制方程的离散在空间上采用有限体积法,时间上采用了具有二阶精度的“预测-校正”法,固壁边界使用“部分滑移”条件,使用该模型对高水头、高转速混流式水轮机流动特性进行计算。结果表明,转轮计算流场分布与实际情况吻合,在部分负荷工况下,叶片出水边存在脱流现象,造成叶片出水边表面出现负压。尾水管直锥段和弯肘段在部分负荷工况下存在较强的旋流,在轴心线附近存在回流现象,并成功地模拟了尾水管中的涡带现象,与实际观测结果一致,该涡带频率为机组旋转频率的三分之一左右,振幅较大,属于低频大幅值性质,是引起机组振动的根源之一。

Research on 3-D Viscous Large Eddy Simulation Model for Hydraulic Turbine

A 3-D viscous combined model adopting the large eddy simulation technology was developed,and employed in simulating the 3-D flow through a high-head and high-rotation hydraulic turbine with the runner calculated in relative coordinate system and the draft tube computed in absolute coordinate system.The finite volume approach in space and the predictor-corrector method in time for the weakly compressible flow governing equations and a "tinny-slip" boundary condition for the solid wall were adopted,and the connected condition at the interface between the absolute coordinate system and the relative coordinate system was established.The pressure and velocity fields in the hydraulic turbine are simulated,which are consistent with the experimental results.Under partial-load operating condition,especially,the separated flow and the negative pressure at the exit surface of the blade of the runner and a strong vortex in the cone and elbow section in the draft tube appear,even the back-flow near center line at entrance of the draft tube is in existence.The demonstration of the vortical band in the draft tube under partial-load operating condition is successfully simulated,and its frequency is about one-third of the rotating frequency of the runner,this vortical band is one of the main reasons for the vibration of the turbine-generator unit.