Simulations of unsteady cavitating turbulent flow in a Francis turbine using the RANS method and the improved mixture model of two-phase flows
Simulations of unsteady cavitating turbulent flow in a Francis turbine using the RANS method and the improved mixture model of two-phase flows
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DOI：
10.1007/s00366-010-0194-6
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发表时间：
2011-07
影响因子：
8.7
通讯作者：
Yulin Wu;Shuhong Liu;H. Dou;L. Zhang
中科院分区：
文献类型：
--
作者：
Yulin Wu;Shuhong Liu;H. Dou;L. Zhang
本文报道了用腔液两相流混合模型对弗朗西斯涡轮机内非定常空化湍流流动的模拟结果。采用RNGk-ε湍流模型求解雷诺平均Navier-Stokes方程。在混合模型中，采用了基于蒸发和冷凝机理的改进的传质表达式，考虑了非溶解气体、湍流、空腔处界面张力和相变速率等因素的影响，计算域包括导流叶片、转轮和导流筒，其用非结构化四面体形状的全三维网格系统离散化。采用有限体积法求解混合物模型的控制方程，并结合全耦合方法加速求解。将混合物模型的计算结果与单相流模型的计算结果以及实验数据进行了比较。模拟结果表明，基于改进混合物模型的空化流计算结果在压力脉动幅值和主导频率方面比单相流计算结果更符合实验数据。模拟结果还表明，小流量时的压力脉动幅度大于大流量时的压力脉动幅度，这与实验结果相吻合。
This paper reports the simulation results for the unsteady cavitating turbulent flow in a Francis turbine using the mixture model for cavity–liquid two-phase flows. The RNGk–εturbulence model is employed in the Reynolds averaged Navier–Stokes equations in this study. In the mixture model, an improved expression for the mass transfer is employed which is based on evaporation and condensation mechanisms with considering the effects of the non-dissolved gas, the turbulence, the tension of interface at cavity and the effect of phase change rate and so on. The computing domain includes the guide vanes, the runner, and the draft tube, which is discretized with a full three-dimensional mesh system of unstructured tetrahedral shapes. The finite volume method is used to solve the governing equations of the mixture model and a full coupled method is combined into the algorithm to accelerate the solution. The computing results with the mixture model have been compared with those by the single-phase flow model as well as the experimental data. The simulation results show that the cavitating flow computation based on the improved mixture model agrees much better with experimental data than that by the single-phase flow calculation, in terms of the amplitude and dominated frequency of the pressure fluctuation. It is also observed from the present simulations that the amplitude of the pressure fluctuation at small flow rate is larger than that at large flow rate, which accords with the experimental data.