Deformation of turbine wake cross-section due to yaw offset and wind veer – Results from CONFLOWS project

In this research, a new analytical model to represent the combined effect of the turbine yaw offset and the inflow vertical wind veer on the downstream wake of a wind turbine is introduced. To take the vertical wind veer into account, two approaches are used. First, the curled (kidney) shape of the wake due to the yaw misalignment is modelled. Later, the effect of lateral deflection due to vertical wind veer at each height was taken into account, assuming that the turbine wake is transported downstream as a function of the incoming flow velocity. In a more realistic approach, the second method considers the effect of wind veer on the wind velocity direction and the variation of yaw angle seen by the wind turbine with height. Accordingly, the model uses a local coordinate system defined based on the wind direction at each height to represent the wake region and then it is transformed to the global coordinate system attached to the ground. The results demonstrate similar outputs for small vertical wind veer changes across the rotor, while the difference is more noticeable with higher values of wind direction changes across the rotor. The model outputs for different operating conditions were also validated by LES simulations in a neutral atmospheric boundary layer.