Assessment of complex wind turbine wake flow using scanning wind lidar measurements and numerical analysis techniques

Utilising scanning lidar devices deployed in active wind farms the results presented detail the evolution of the wind speed profile in the wake of wind turbines operating in both the on and offshore environment. The results of each of the deployments are compared against a variety of wake simulation models. Focussing on the measurement of wake data at hub height, data captured from the nacelle of an offshore wind turbine detailing flow evolution behaviour across a wide range of operational wind speeds and inlet operating conditions is presented. Binned in 2m/s wind speed bins the measurements clearly show a consistent profile across the captured speed range. This profile encompasses an initial flow deficit from inlet measured on the downstream side of the rotor. For undisturbed inflow this is seen to be around 30%, slightly larger for the disturbed inflow and larger still for waked inflow. Moving downstream the measured flow values indicate a flow evolution to a maximum deficit from inlet at two rotor diameters downstream, the differences between the inflow situations are preserved through to this point. This deficit is at a maximum in the 6-8m/s wind speed bins where the Power Coefficient is at its highest. As the wind speeds increase, and the Power Coefficient decreases, the magnitude of the maximum deficit decreases. Beyond this point the flow recovers towards inlet values. None of the profiles are found to recover fully within thirteen rotor diameters of the rotor plane. The wake simulation models employed each identify different areas of strength in comparison to the lidar measurements. The Eddy-Viscosity model with a Turbulence Intensity of 6% shows the closest correlation with the results at the maximum deficit through the recovery and into the far wake. It does not attempt to model the flow behaviour in the near wake region.Utilising scanning lidar devices deployed in active wind farms the results presented detail the evolution of the wind speed profile in the wake of wind turbines operating in both the on and offshore environment. The results of each of the deployments are compared against a variety of wake simulation models. Focussing on the measurement of wake data at hub height, data captured from the nacelle of an offshore wind turbine detailing flow evolution behaviour across a wide range of operational wind speeds and inlet operating conditions is presented. Binned in 2m/s wind speed bins the measurements clearly show a consistent profile across the captured speed range. This profile encompasses an initial flow deficit from inlet measured on the downstream side of the rotor. For undisturbed inflow this is seen to be around 30%, slightly larger for the disturbed inflow and larger still for waked inflow. Moving downstream the measured flow values indicate a flow evolution to a maximum deficit from inlet at two rotor diameters downstream, the differences between the inflow situations are preserved through to this point. This deficit is at a maximum in the 6-8m/s wind speed bins where the Power Coefficient is at its highest. As the wind speeds increase, and the Power Coefficient decreases, the magnitude of the maximum deficit decreases. Beyond this point the flow recovers towards inlet values. None of the profiles are found to recover fully within thirteen rotor diameters of the rotor plane. The wake simulation models employed each identify different areas of strength in comparison to the lidar measurements. The Eddy-Viscosity model with a Turbulence Intensity of 6% shows the closest correlation with the results at the maximum deficit through the recovery and into the far wake. It does not attempt to model the flow behaviour in the near wake region