【作者】 黄剑峰；

【导师】 张立翔；

【作者基本信息】 昆明理工大学 ， 工程力学， 2013， 博士

【摘要】 水轮机是水力发电系统中的核心部件,工作在旋转湍流下会产生非定常压力脉动、空化、泥沙磨损、流激振动等严重影响机组正常运行的问题。研究该类问题具有工程实际意义和理论学术价值。数值模拟已成为当前研究水轮机内部流场及其复杂流动机理的重要工具。本文采用现代计算流体动力学中的先进数值模拟方法,围绕困扰水轮机领域安全高效稳定运行的一些技术难题开展工作,研究内容和取得的成果如下：(1)基于三维瞬态N-S方程,采用大涡模拟(LES)方法中的Smargorinsky-Lilly亚格子应力模型,应用模拟动静干扰效果较好的滑移网格技术,以标准k-ε湍流模型稳态计算的结果作为初始条件,对某原型混流式水轮机全流道进行了三维瞬态湍流数值模拟。采用非结构化的混合网格和压力速度耦合的PISO算法,成功地模拟了水轮机在运行中的各种瞬态细节过程,如涡旋的卷起、增长、合并、破碎和脱落。模拟结果给出了偏工况下水轮机导水机构和转轮流道内大尺度涡结构的瞬态发展演变过程。计算结果表明大涡模拟方法能较好地模拟水轮机内水流的瞬态流动特性和瞬时涡的发展演化过程,该方法可为探索研究水力机械复杂流道湍流运动状态下涡旋的形成机理提供有价值的参考。(2)基于不可压缩流体瞬态N-S方程对混流式水轮机内部三维非定常流进行精细模拟分析,以标准k-ε湍流模型对水轮机进行全流道定常计算的结果作为初始流场,应用较新的分离涡模拟(DES)和滑移网格技术进行了水轮机考虑两级动静干扰的非定常湍流数值模拟,得到了偏工况下活动导叶出口及转轮叶道内涡量场及速度场分布特性。模拟了大尺度涡旋结构的卷起、发展等瞬态演化过程,结果表明DES方法可以更加全面真实地模拟水轮机内部的流动情况,捕捉到水力机械中复杂流道内的三维动态涡结构。该研究对于探讨影响水力发电机组出力摆动的水轮机涡激振动的内在机理、确保机组的安全稳定运行具有重要意义。(3)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,加入考虑气穴影响的Schnerr and Sauer空化模型,采用标准k-ε湍流模型和压力速度耦合的SIMPLEC算法,转动区域应用多重参考系模型(MRF),对某原型混流式水轮机全流道进行了三维定常空化湍流数值模拟。获得了该水轮机在偏工况下转轮叶道和尾水管内空泡相的主要流动特征,分析了水轮机流道内空化发生的部位与程度。计算结果表明与单相流体模型相比该方法能有效地预测水轮机内的三维空化湍流场,可以较好地模拟水轮机内真实的有空化发生的多相流动情况,对揭示水力机械内部包含气穴影响的气液两相流场的内在特性、优化水轮机的水力设计和改善水轮机的空化性能具有重要参考价值。(4)基于欧拉-欧拉方法中的代数滑移混合多相流模型,采用标准k-ε湍流模型和多重参考系模型(MRF),对某原型混流式水轮机全流道进行了三维定常泥沙磨损湍流数值模拟。获得了该水轮机在偏工况下转轮叶道和尾水管内泥沙颗粒相的体积分数分布,分析了水轮机流道内泥沙磨损的特征规律。计算结果表明该方法能有效地预测水轮机内的三维泥沙磨损固液两相湍流场,可以较好地模拟水轮机内真实的有泥沙磨损发生的多相流动情况,对揭示水力机械内部包含泥沙颗粒影响的固液两相流场的内在特性、提高水轮机的运行效率和改善水轮机的磨蚀性能具有重要参考价值。(5)基于任意拉格朗日欧拉框架下的二维时均瞬态N-S方程,应用非结构动网格技术,对某型号混流式水轮机单个活动导叶在槽道内模拟导水机构在一段直线关闭规律和两段折线关闭规律下的关闭过程,进行了动态湍流数值模拟。采用非结构化三角形网格,标准k-ε湍流模型和压力速度耦合的PISO算法,真实地模拟了导水机构关闭的动态过程中活动导叶流道内的压力场、速度场和湍流特性的瞬态变化过程。数值计算结果表明,在两种导叶关闭规律过程中,随着活动导叶开度的减小,流场发展呈现明显的非定常特性,水流绕过活动导叶后出现强的旋涡,会对水轮机过渡过程的动态特性产生影响。该方法能有效地模拟由于活动导叶动作诱发的流场脉动。(6)基于三维非定常不可压缩粘性流体N-S方程,用浸入边界法(IBM)处理活动导叶运动产生的动边界,大涡模拟(LES)的亚格子应力(SGS)使用动态Smagoringsky-Lilly模型,对槽道内某混流式水轮机单个活动导叶翼型、双列线性动静叶栅及导水机构双列非线性环列叶栅动态绕流场进行了瞬态湍流精细数值模拟。计算很好地捕捉了活动导叶关闭动作典型时刻压力和分离尾迹涡拓扑结构随时间的变化规律。结果表明,活动导叶的调节运动动态绕流将产生大量而复杂的瞬态流动结构,其向上在管道系统中诱发水击波动,向下影响转轮叶道中的暂态特性。本文提出的基于Smagoringsky-Lilly动态SGS模型的LES-IBM方法可有效地模拟高雷诺数下活动导叶关闭运动与叶道湍流之间的相互作用过程,揭示水轮机调节过程中活动导叶动态绕流尾迹结构产生的机制及其向下游方向的演化特性。更多还原

【Abstract】 As a core component of hydroelectric system, hydraulic turbine will be confronted with serious questions such as unsteady pressure pulsation, cavitation, silt abrasion and flow-induced vibration, which will influence hydraulic turbine work. The study of such problems has practical significance as well as theoretical values. Numerical simulations are an important tool to study the internal flow features for a Francis hydro-turbine. The dissertation mainly focuses on several technical problems which are affecting the high efficiency and the stable operation of hydraulic turbine by using the state-of-the-art numerical methods in modern computational fluid dynamics. The main work and results are stated as following.(1) Numerical simulation of three dimensional transient turbulent flow in the whole flow passage of a Francis hydro turbine based upon the Reynolds averaged Navier-Stokes equations was conducted with the large eddy simulation (LES) technique on Smargorinsky-Lilly model and sliding mesh technology. The steady flows simulated with the standard k-ε model were used as the initial conditions of the flow in the unsteady simulation. The large scale structures evolving in spatially and temporally were visualized by using unstructured hybrid-grid and PISO algorithm. The evolution details of the large scale structures such as eddy from generate to shedding in vane cascades and blade passages are well captured at special case. The results show that LES can simulate well transient turbulent flow and its evolution in a Francis hydro turbine with complex geometry. The computational method provides some reference for exploring mechanism of eddy formation in a complex turbulent of hydraulic machinery.(2) Finely numerical simulation of the three-dimension unsteady turbulent flows in whole flow passage of a Francis hydro-turbine based on the uncompressible viscous Navier-Stokes equations was conducted. The steady turbulent flow was firstly simulated with the standard k-ε model in different opening cases of the moving guide vanes and then used as the initial flow of the unsteady flow to be simulated. The detached eddy simulation (DES) and the sliding mesh technique were applied to the simulation of the unsteady turbulent flow. The flow structures in the turbine in the different opening cases were well captured, and the evolving of the large scale structures was finely shown spatially and temporally. The results show that DES is able to well simulate the unsteady turbulent flow and to obtain the finely dynamic eddy structures in a Francis hydro-turbine. The research relies on the understandings of the vibrating of a hydro-turbine due to the turbulent flow.(3) The numerical simulation of three dimensional cavitation turbulent flow in Francis hydro-turbine passage was conducted based on the mixture model for homogeneous multiphase flow hypothesis in the Euler-Euler approach and the Schnerr and Sauer cavitation models. The standard k-s model, SIMPLEC algorithm and multiple reference frame model were used. The distributions of the water-vapor volume fraction in blade passage and draft tube were obtained in special case. The position and degree of cavition in turbine passage were analyzed. The results show that the method can be used to simulate the3D cavitation turbulent flow and true multiphase flow with cavitation in Francis turbine than one-phase model. The calculation provides significant reference for revelation the feature of gas-liquid phase flow of hydraulic machinery and optimal design for the runner. The study is valuable for improving the cavitation of performance in Francis turbine.(4) The numerical simulation of three dimensional two phases turbulent flow in Francis hydro-turbine passage was conducted based on the mixture model for an algebraic slip formulation in the Euler-Euler approach. The standard k-s model, SIMPLEC algorithm and multiple reference frame model were used. The distributions of the silt volume fraction in blade passage and draft tube were obtained in special case. The position and degree of silt abrasion in turbine passage were analyzed. The results show that the method can be used to simulate the3D turbulent flow and true multiphase flow with silt abrasion in Francis turbine. The calculation provides significant reference for revelation the feature of solid-liquid phase flow of hydraulic machinery and improved hydraulic performance. The study is valuable for improving the abrasion of performance in Francis turbine.(5) The numerical simulation of two dimensional transient turbulent flow in a guide vane passage of wicket gate in a benchmark hydro-turbine was conducted based on the ALE(Arbitrary Lagrangian-Eulerian) and dynamic mesh technology. The dynamical changes of the pressure, velocity and turbulence characteristic are simulated, using unstructured-triangle grid, standard k-ε turbulence model and PISO algorithm as the guide vane is moving at linear and polyline closure. The results show that the evolution of the flow field is unsteady with decrease of the vane opening. Based on these researches, the eddy structures evolving spatially and temporally were visualized. The calculation provides some reference for vortex-induced vibration in a complex turbulent flow of hydraulic machinery. The study is valuable for simulating the turbulence induced by the guide vane adjustment.(6) The fine numerical simulation of three dimensional dynamic turbulent flow around one moving guide vane in a channel, linear and nonlinear oscillating cascade of the wicket gate of a benchmark hydro turbine unit was conducted based on the uncompressible viscous Navier-Stokes equations flow and immersed boundary method (IBM) for moving boundary. The dynamical subgrid stresses (SGS) on Smagorinsky-Lilly model was used in large eddy simulation (LES). The distributions of the pressure and the topological structures of wake were well captured as closure of the vane. The production and evolution of the wake vortices passing the kinetic guide vane was clearly shown, and the physics of the structures were analyzed. The results show that the flow around a moving guide vane will be produced numerous complex transient structure whose induce water hammer of upstream duct system and transient behavior of downstream runner passage. The numerical results show that the numerical method of LES-IBM with dynamical Smagorinsky-Lilly SGS model is able to well simulate the interaction between high Reynolds number turbulent flow with motion of the vane closure and reveal the mechanism evolution properties of the wake to the downstream in the hydro turbine adjustment process.更多还原