Numerical Studies of the Upstream Flow Field around a Horizontal Axis Wind Turbine

Paper in proceeding, 2015

The aerodynamics of a wind turbine is governed by the flow around the rotor. Prediction of the velocity field, both upstream and downstream, is one of the challenges for wind turbine performance in terms of the aerodynamic loads and the generated power at different operational conditions. For simplicity, the wind velocity at the rotor plane is assumed to be equal to far upstream flow where the interaction of the rotor blades with upstream flow, close to the rotor plane, is not taken into account. This paper aims to study the effect of the rotor blade azimuthal position and the trailing wake, on upstream and downstream flow near to the rotor plane. 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. They show that the wind speed decreases in the axial direction upstream the rotor plane because of the induced velocity field by the rotor blades and the trailing wake vortices. This leads to a power reduction of the wind turbine. Furthermore, contrary to the traditional actuator disk model, the VLFW simulations predicts a tangential velocity component upstream the rotor due to the blade rotation which is in agreement with the measurement data. Finally, it is found that the flow field downstream and upstream the rotor blades depends on the blade azimuthal direction.