基于CFD混流式水轮机转轮空化及涡旋流动数值模拟

Numerical simulation of the cavitation and vortex flow of francis turbine runner based on CFD

采用RNK湍流模型和压力速度耦合的SIMPLEC算法,基于欧拉-欧拉方法中均匀多相流假设的混合两相流体无滑移模型,选用Schnerr and Sauer空化模型,对混流式水轮机转轮进行三维空化湍流数值模拟。利用ANSYS CFX,通过转轮的汽含率云图、流线图、turbo面分析以及转轮进出口压力、速度曲线分析,获得了该水轮机在大开度、小开度下的转轮、叶片以及泄水锥的空泡、涡旋黏度等主要流动特征。计算结果表明:大开度和小开度对转轮的空化影响不同,存在一定规律,即大开度下空化严重而范围比较集中;小开度下空化较轻但发生范围较广;大开度下涡旋黏度偏大,则空泡不宜脱流,即不容易在叶片上产生漩涡;小开度则涡旋黏度小,即叶片上漩涡明显。

In this paper,the SIMPLEC algorithm which coupled RNK turbulence model with pressure-velocity was applied to numericaly simulate three-dimensional cavitating turbulent of Francis turbine runner based on mixed two phase fluid no sliding model of Euler-Euler method with the assumption of homogeneous multiphase flow. The Schnerr and Sauer cavitation models were selected. Using the software of ANSYS CFX,with the runner gas-holdup cloud,based on the flow chart,turbo-surface analysis,runner pressure or velocity curve analysis,the main flow characteristics of Francis turbine runner about cavitation and vortex viscosity in the large and small open flow were obtained. The calculation results showed that the effects of cavitation on the runner under the large and small open flow were different and there occurred certain law,i. e.,under large open degree,there was more severe cavitation and the scope was concentrated;while under small open degree,there was slight cavitation but the occurrence areas was large. There was large eddy viscosity under large opening,the cavity was not easy to take off flow,i. e.,it was not easy to produce vane vortex. At a small open degree,the eddy viscosity was small,the vortex was obvious on the blade.