Numerical study of wind shear effects on the aerodynamics and wake field of wind turbines

Abstract

Inhomogeneous and unsteady inflow wind speed caused by wake to the downstream wind turbine impairs its aerodynamic performances inevitably. To attenuate the adverse effects of the wake, the underlying flow mechanism of three-dimensional unsteady and rotational wake should be understood in depth. This paper investigates wind shear effects on the wake profile and the aerodynamic characteristics of wind turbines. Aerodynamic performances and wake flow of a scaled-down NREL 1.5 MW wind turbine are predicted numerically. Unsteady Reynolds-Averaged Navier-Stokes equations, the k-. SST turbulence model and the sliding mesh method are used. The calculated velocity profiles of the wake are validated against the windtunnel experimental data. The simulation results show that the combined effects of wind shear and tower shadow can produce periodic fluctuations of the aerodynamic thrust and the torque of rotating blades. When the wind shear coefficient increases from 0 to 0.2, its thrust and torque are reduced by 0.4% and 1.4% respectively. On the other hand, the tower also leads to the asymmetry velocity profile of the wake. This implies that the combined effects of wind shear and tower shadow significantly complicate the wake flow. This work might contribute to improving the aerodynamic modelling of the three-dimensional wake flow.