Numerical Analysis On Flow Characteristics In Full Flow Passage Of Francis Turbine

Francis turbine has been widely used with the characteristics of wide application scope, simple structure and reliable operation. The runner is a core component of water turbine generator set, and the flow state in a turbine runner directly affects the energy characteristics of the entire machine and the stability of the unit. Therefore, the design of runner is very important. The flow state in the runner and the running performance under different conditions are analyzed by using the CFD numerical simulation method. It is an important means for the optimization design of runner. The developments of domestic and foreign large-scale hydropower units are all based on this means for the development and optimization of new runners.The geometric model of full flow passage of water turbine is established on the basis of geometric parameters of a prototype Francis turbine in a hydropower station. By using 3-dimensional modeling software UGNX, the data of various wood-mould sections are introduced into UGNX software in the format of ".dat" by aiming at the data conversion of wood-mould drawing to be solved in the solid modeling of the runner of Francis turbine and by adopting fixed mesh division in CAD. Cubic spline surface method is adopted to recreate the turbine blade in UGNX, and numerical model for the fitting of turbine blade surface is provided for the analysis of flowing property of water turbine. The turbine runner model established in UGNX is introduced into gambit software. The meshes flow passage components are divided by adopting unstructured hybrid tetrahedral mesh. The steady field in A696 Francis turbine runner is numerically simulated by using FLUENT software. Many external properties such as excess flow, efficiency and other energy responses of the runner blade are analyzed in different running conditions. The cavitation performance of runner is foreseen according to the pressure distribution at the front and back of the runner. This provides more valuable references for the predication of runner performance.In addition, with the improving of water turbine efficiency, the operational stability and vibration of hydraulic units have drawn more and more attentions. In fact, the fluid flow among flowing components in the water turbine is a very complicated 3-dimensional unsteady viscous fluid movement. So only the calculation of steady flow field in water turbine is not enough to predict the stability of hydraulic unit, and the simulation and calculation of unsteady flow field in the water turbine is necessary. The mutual interference of flow between runner and guide vane and between runner and draft tube will lead to unsteady flow in the flow passage, and therefore affect the stability of the unit. Therefore, it is necessary to study the unsteady flow field in water turbine. The unsteady flow field in water turbine in this paper is analyzed after the convergence of steady flow field. The generating mechanism and characteristics of various kinds of vortexes in unsteady flow field in Francis turbine are studied. Effective methods to reduce the adverse effect of vortex are obtained.