【作者】 胡英；

【导师】 程赫明；

【作者基本信息】 昆明理工大学 ， 工程力学， 2008， 博士

【摘要】 水轮机中的流动是非定常的三维粘性不可压缩紊流流动,三维非定常紊流流动的研究一直是水轮机流场研究中所面临的难题。由于混流式水轮机组向大型化发展的趋势中,振动问题愈显突出,流场不稳定现象是引起振动的主要原因之一,因而对水轮机非定常紊流流场的研究就凸显重要。在水轮机研究开发中,流态解析和性能预测则是不可或缺的手段,水轮机外特性与流场流态密切相关,只有具有良好的流态分布,才会有优良的外特性指标和性能。目前,国内外在该领域前沿的研究视角多为采用CFD分析软件计算和模拟流场。针对非定常紊流计算在混流式水轮机研究领域中的重要地位,本文确定了将非定常紊流计算作为其主要研究内容。本论文的研究框架和方法主要为：(1)进行了混流式模型水轮机转轮中的非定常紊流计算。在三维时均N-S方程的基础上,运用Realizable k-ε模型及CFX-TASCflow软件对一混流式模型转轮进行了三维非定常紊流计算,数值模拟了转轮内部三维紊流流场,且通过模型水轮机的外特性试验证明了该计算可较真实地模拟模型转轮的内部流动,流场计算结果合理。(2)根据流场计算结果预测了该模型转轮的能量性能、空化性能,并与试验值进行了比较,结果表明,计算所得的效率值和空化系数与实测值比较接近,从而提升、丰富了现有的水轮机设计方法(3)进行了混流式模型水轮机全流道中的非定常紊流计算。运用CFX-TASCflow软件和RNG k-ε紊流模型计算了混流式模型水轮机全流道三维非定常紊流,得到了蜗壳、导水机构和尾水管内的瞬时流场及蜗壳进口、固定导叶进出口、转轮前和尾水管内压力场的脉动频率和幅值。通过标准k-ε紊流模型与RNG k-ε紊流模型的比较计算,显示出了尾水管内的旋转涡带现象。经与试验结果比较,RNG k-ε紊流模型比标准k-ε紊流模型能更好地模拟由自激引起的非定常流动,计算结果与实际情况较为符合。通过模型水轮机全流道瞬变流计算,不仅模拟到转轮前的压力脉动,而且模拟出尾水管中非定常涡带,从而预估出了水轮机中的水力非稳定现象。本研究可对正确进行水轮机全流道三维非定常紊流计算提供一定的参考本文所取得的研究成果充实了水轮机研发设计领域的理论研究成果。对优化混流式水轮机的设计,提高水轮机的效率,缩短研发周期,准确预测水轮机的水力性能,具有较好的理论指导意义及技术支持,且具有较强的工程应用价值。更多还原

【Abstract】 The flow in a hydraulic turbine is three-dimensional viscid, incompressible and unsteady turbulent flow. The research on a 3D unsteady turbulent flow is a challenging problem, which the study of the flow field in a turbine has to face. As hydraulic turbines are developed toward large-sized, the problem of vibration is becoming more prominent. The unsteady flow phenomena are one of the main reasons that cause vibrations. Therefore, it is of great importance for research on the unsteady turbulent flow in a turbine. Nowadays, in the field of research and development of a hydraulic turbine, computation fluid dynamics (CFD) has become an indispensable method for analyzing the flow patterns and predicting turbine performance. Turbine characteristics are closely related to the state of flow in a flow field. Only if the flow is well distributed, a turbine has excellent characteristics and performance. In all advanced flow research all over the world, the CFD analysis is applied to calculate and simulate a flow field, hence to predict the efficiency of a runner and the performance of cavitation.The numerical simulation on the unsteady turbulent flow characteristics of Francis turbines flow filed has a great importance for turbine research. This thesis focuses on the unsteady turbulent flow calculations and its analysis. The framework of theoretical studies and methods in this dissertation are as follows:(1) Unsteady turbulent flow simulation in a model Francis turbine runner. Based on the 3D time average N-S equations, the 3D unsteady turbulent flow in a model Francis turbine runner is numerically simulated using realizable k-εturbulent model and CFX-TASCflow software. The calculation has been proven by characteristic tests of the model turbine. The reasonable comparison of the calculation and experiment reveals that the inner flow in the model runner may be truly simulated.(2) The energy and cavitation performances are predicted by means of numerical simulation. Compared with the test results, it shows that the computed efficiency and cavitation coefficient agree with the experiment data. The numerical calculation methods has improved and enriched the hydraulic turbine design.(3) Unsteady turbulent calculation in an entire model Francis turbine. The 3D unsteady turbulent flow in an entire model Francis turbine is simulated using the RNG k-sturbulent model and CFX-TASCflow software. Transient flow fields are simulated in the spiral casing, including the entire stay vane ring, and the draft tube. Based on the standard k-εmodel and RNG k-εmodel, the whirl vortexes in the draft tube are simulated. In comparison with the experimental data, it concludes that the self-stimulated unsteady flow is simulated better with RNG k-εmodel than the standard k-εmodel. The results computed with RNG k-smodel are in good agreement with experiment data. We simulated not only the pressure fluctuation in front of the runner, but also the unsteady vortex in the draft tube by means of the unsteady flow computation in an entire model turbine. Thus, the realistic hydraulic unsteady phenomena occurring in the turbine was predicted. The result shows that this research provides the great value on calculating 3D unsteady turbulent flow in an entire turbine accurately.The results of this study fill up deficiencies on the theoretical research in the studying and developing fields of a hydraulic turbine. These provide significant theoretical guide and technical support to optimize the design of a Francis turbine, to increase the efficiency, to shorten the time of research and development, to accurately predict the hydraulic performance. It will be valuable in engineering application.更多还原