Wind tunnel experiments on wind turbine wakes in yaw: effects of inflow turbulence and shear

The wake characteristics behind a yawed model wind turbine exposed to different customized inflow conditions are investigated. Laser Doppler anemometry is used to measure the wake flow in two planes at x/D = 3 and x/D = 6, while the turbine yaw angle is varied from gamma = 30 degrees to 0 degrees to +30 degrees. The objective is to assess the influence of grid-generated inflow turbulence and shear on the mean and turbulent flow components. The wake flow is observed to be asymmetric with respect to negative and positive yaw angles. A counter rotating vortex pair is detected creating a kidney-shaped velocity deficit for all inflow conditions. Exposing the rotor to non-uniform highly turbulent shear inflow changes the mean and turbulent wake characteristics only insignificantly. At low inflow turbulence the curled wake shape and wake center deflection are more pronounced than at high inflow turbulence. For a yawed turbine the rotor-generated turbulence profiles peak in regions of strong mean velocity gradients, while the levels of peak turbulence decrease at approximately the same rate as the rotor thrust.