How to extrapolate 3D aerodynamic coefficients from HAWT CFD simulations: an inverse BEM approach

In the present work the authors developed a methodology based on an inverse BEM method, to easily extrapolate 3D aerodynamic coefficients from HAWT CFD 3D simulation results. Specifically, since the BEM method was based on the solution of a discrete number of blade radial sections, the CFD model was implemented in Ansys Fluent in such a way to split the surface of one of the blades in a certain number of sections already at the CAD level. Therefore, the normal and tangential aerodynamic forces were calculated for each radial section and subsequently provided directly within the modified BEM code developed in Matlab. Thus, the BEM code iterated for the axial and tangential induction factors and calculated the lift and drag coefficients, the related local angle of attack, the torque, the power and the power coefficient for each specific operating condition simulated. The methodology proposed here was validated using the NREL Phase VI rotor geometry for which a very good agreement between numerical and experimental data was found. Furthermore, this allowed for an insight into the 3D effects over the blade since it was possible to compare the experimental 2D and the 3D lift and drag coefficients section by section.