Turbulent flow computation through a model Francis turbine and its performance prediction

In this paper an improved k-omega turbulence model is proposed, which brings the nonlinear term of the mean fluid flow transition to the. equation in the original k-omega model of Wilcox. Based on the improved k-omega turbulence model, three dimensional turbulent flow computation is carried out through the whole flow passage including the spiral casing, stay vanes, guide vanes, runner and draft tube of a model Francis turbine. In calculation the direct coupling method is used to solve the RANS turbulent flow governing equations for the Francis model turbine by Ansys CFX software. Since the feasibility of the improved k-omega turbulence model to hydro-turbine performance prediction is the present main concern, its validation is conducted by the steady flow simulation. Comparisons of the computational results on energy characteristics with test data and with different turbulence models at different flow rate cases indicate that the present method has sufficient potential to simulate the turbulent flow in hydraulic turbines and to predict their performances.