Effect of Di erent Geometries in Simulation of 3D Viscous Flow in Francis Turbine Runners

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares di erent geometries for numerical investigation of the 3D ow in the runner of a Francis turbine, and presents an optimum geometry with least computational e ort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal ows, 1989) in which the geometry and detailed best eciency measurements were publically accessible. In this simulation, the ow is assumed to be steady and the inlet boundary condition is prescribed using experimental data. The e ect of turbulence is considered by the k 􀀀" model. The present investigation demonstrates that consideration of 2-blade geometry with periodic boundary conditions is the best choice of computational domain. By 1-blade geometry, convergence of the numerical simulation is not appropriate, whereas 13-blade geometry leads to a coarse grid that can increase inaccuracy and computational cost. Finally, this paper presents a qualitative survey to forecast cavitation region inception which correlates satisfactorily with experimental observations.