The effects of freestream turbulence and shear flows on the near-field wake of a lab-scale wind turbine

Wind turbines experience a wide range of turbulent shear flows within the atmospheric boundary layer, which is challenging to replicate in a wind tunnel setting. The classical methods of using passive flow conditioning devices to modify wind tunnel boundary layers has had limited success due to their inherent inability to separate shear from turbulence intensity. The present study uses an active grid to decouple shear and turbulence intensity in order to investigate their separate effects on the near field wake of a wind turbine model. A total of 7 flow profiles were created that covered a wide range of turbulence intensities and shear profiles. PIV results show that incoming flow conditions do not have a major influence on wake geometry compared to the incoming flow. Turbulence production in the wake under shear conditions skews toward the high velocity side. This in turn leads to higher variance in the local wake boundary. The behaviour of the hub velocity contour line before and after the blades are affected by shear only. Overall the macroscopic properties of the wake are not affected by incoming flow conditions, however shear has greater impact on velocity profile and turbulence production within the wake than turbulence intensity.