Abstract: This paper presents a study of laminar to turbulent transition on a profile specifically designed for wind turbine blades, the DU91-W2-250, which belongs to a class of wind turbine dedicated airfoils, developed by Delft University of Technology. A comparison between the experimental behavior of the airfoil studied at Delft wind tunnel and the numerical predictions of the commercial CFD solver ANSYS FLUENT® has been performed. The prediction capabilities of the Spalart-Allmaras turbulence model and of the γ-θ Transitional model have been tested. A sensitivity analysis of the numerical results to the spatial domain discretization has also been performed using four different computational grids, which have been created using the mesher GAMBIT®. The comparison between experimental measurements and CFD results have allowed to determine the importance of the numerical prediction of the laminar to turbulent transition, in order not to overestimate airfoil friction drag due to a fully turbulent-regime flow computation.
Abstract: This paper presents a numerical analysis of the
performance of a three-bladed Darrieus vertical-axis wind turbine
based on the DU91-W2-250 airfoil. A complete campaign of 2-D
simulations, performed for several values of tip speed ratio and based
on RANS unsteady calculations, has been performed to obtain the
rotor torque and power curves. Rotor performances have been
compared with the results of a previous work based on the use of the
NACA 0021 airfoil. Both the power coefficient and the torque
coefficient have been determined as a function of the tip speed ratio.
The flow field around rotor blades has also been analyzed. As a final
result, the performance of the DU airfoil based rotor appears to be
lower than the one based on the NACA 0021 blade section. This
behavior could be due to the higher stall characteristics of the NACA
profile, being the separation zone at the trailing edge more extended
for the DU airfoil.