The near-field of a lab-scale wind turbine in tailored turbulent shear flows

Real wind turbines experience a wide range of turbulent shear flows that naturally occur within the atmospheric boundary layer, however, these are often difficult to simulate in experiments. An active grid was used to expand the testable parameter space compared to conventional methods. Specific focus was placed on decoupling the shear from the turbulence intensity. Particle image velocimetry was used to capture the mean velocity and velocity fluctuation fields in the near-field wake of a model wind turbine subjected to seven different combinations of shear and turbulence intensity. It was found that if the incoming mean profile was removed, the velocity deficit is approximately symmetric about the hub, even for highly sheared cases. The absolute wake velocity deficit profiles are asymmetric for the sheared cases, and the combination of the wake and shear flow results in a local increase in shear on the high-velocity side of the wake immediately downstream of the turbine. This in turn leads to higher turbulence production within that region, leading to larger velocity fluctuations. It is also demonstrated that the mean power of the model turbine is not particularly sensitive to the incoming shear, but the power fluctuations scale linearly with the incoming turbulence intensity.