Development of Free Vortex Wake Model for Wind Turbine Aerodynamics under Yaw Condition

The aerodynamics of a wind turbine is governed by the flow around the rotor. One of the most severe operating conditions for a wind turbine is the yaw misalignment, when the mean upstream flow is not perpendicular to the rotor plane. This asymmetrical flow changes significantly the velocity field around the rotor blades which in turn reduces power production of the wind turbine. It also makes a periodic load variation along the rotor blade which accordingly increases the fatigue load from the design point of view. In this paper, the effect of the skewed wake, due to the yaw misalignment, on the wake aerodynamics of wind turbine is studied. For this purpose, an in-house Vortex Lattice Free Wake (VLFW) code, based on the potential, inviscid and irrotational flow, is developed. The results are compared with the MEXICO wind tunnel measurements. For the axial traverses, there is a good agreement between the measured axial (w) and tangential (u) velocity components and the simulations. Although the magnitude of the mean radial velocity component (v) is fairly well predicted, its fluctuation is not captured by the simulation. Moreover, for the radial traverses, the simulations are remarkably verified by the measurements