An investigation of flow fields around flanged diffusers using CFD

Numerical investigations are carried out for flow fields around flanged diffusers to develop small-type wind turbines under 1.5 kW. In the calculations, an advanced closure approximation is adopted, within the framework of non-linear eddy-viscosity modeling, which aims specifically at an improved representation of turbulence anisotropy. Comparison of the computed results with the corresponding experimental data shows that the present calculation has the capability of providing reasonable predictions for the present complex turbulent flows. Furthermore, by processing the computational results, the input-power coefficient is estimated under various conditions of diffuser opening angle and loading coefficient. It is shown that the performance of a flanged diffuser strongly depends on the loading coefficient as well as the opening angle because it greatly affects the nature of the separation appearing inside the diffuser. The present investigation suggests that the loading coefficient for the best performance of a flanged diffuser is considerably smaller than that for a bare wind turbine.