混流式水轮机上冠空腔结构内部流场及单向流固耦合分析

为研究上冠空腔结构对混流式水轮机水力性能与结构特性的影响，建立了不含上冠空腔结构（No UpperCrown Cavity Structure，NUCCS）和含上冠空腔结构（Upper Crown Cavity Structure，UCCS）的两种混流式水轮机全流道几何模型，基于SST湍流模型、顺序耦合法、预应力模态分析，对NUCCS与UCCS的两种混流式水轮机展开数值模拟和单向瞬态流固耦合计算，发现泄水锥处上冠空腔结构可减少转轮内部二次流动损失。在0.8Q_d、Q_d和1.2Q_d的3种流量工况点，分别对混流式水轮机展开瞬态流固耦合计算，对比研究转轮结构的应力应变特性。研究发现含UCCS时，转轮等效应力和变形量均有减小。在小流量0.8Q_d工况点，转轮结构等效应力及应变较小，其最大变形点位于下环附近。在设计流量Q_d和大流量1.2Q_d工况点，转轮等效应力及应变较大，其最大变形点位于上冠附近。在NUCCS与UCCS的转轮进行预应力模态分析时，发现上冠空腔结构对转轮的模态影响很小。本文研究内容可为提升混流式水轮机设计水平提供一定参考依据。

Numerical simulation of fluid-solid coupling of a Francis turbine with an upper crown cavity

In order to study the influence of the upper crown cavity on the hydraulic performance and structural characteristics of the hydraulic turbine, a geometric model of the whole passage of the hydraulic turbine including the clearance passage and the upper crown cavity is established. Based on the SST Turbulence model,the numerical simulation is carried out for the two kinds of runner with and without the clearance and cavity,and the one-way fluid solid coupling calculation is carried out. It is found that the upper part reduces the negative pressure at the discharge cone and reduces the backflow caused by the negative pressure in the runner. The fluid structure coupling calculation is carried out for the turbine with three flow rates of 0.8Q_d, Q_d and 1.2Q_d. The stress-strain characteristics of the runner structure under three flow conditions are compared and studied. It is found that the equivalent stress and deformation of the runner structure are reduced when the upper crown clearance and cavity are considered. Under the flow rate of 0.8 Q_d, the equivalent stress and strain of the runner structure are small, and the maximum deformation point is near the ring. Under Q_d and 1.2 Q_d flow conditions,the equivalent stress and strain of runner are large,and the maximum deformation point is near the upper crown of blade. The pre stress modal analysis of runner with and without upper crown cavity and clearance is carried out, and the results show that the influence of upper crown cavity and clearance on runner modal is very small. The research content of this paper can provide some reference for the design of turbine clearance in numerical simulation, the application and improvement of turbine crown cavity structure.