Evaluation of the radial flow effects on micro HAWTs through the use of a transition CFD 3D model - Part II: Post-processing and comparison of the results

The importance and the complexity of the phenomena related to the development of radial flows is demonstrated in the first part of this paper. In order to further study the radial flow effects and to extend the analysis to laminar and transitional flows, the authors used a CFD 3D model, validated in the wind tunnel owned by the University of Catania. In the second part of this paper, the authors describe the strategy which was used to post-process the simulation results. Furthermore, a comparison of the results was made. Several simulations were first carried out at various wind and rotational speeds. Angles of Attack and aerodynamic coefficients were evaluated on cylindrical surfaces at different radial stations using the ANSYS Fluent Solver and ANSYS Post. Local velocities and forces, related to the sectional airfoil, were obtained in each cylindrical surface along with pressure coefficient distributions. In this way, it was possible to demonstrate the close relationship between radial flows and the strong depressurization of the suction side of the blade. Moreover, the results proved that the increase of lift and drag coefficients is linked to rotational speed and Angle of Attack as well. The radial effects were found to be enforced by laminar and transitional flows related to low Reynolds numbers. This will affect both design and analysis of wind rotor performance, more so than that which was originally suggested by empirical stall delay models.