Wake Dynamics of Wind Turbines for Various Operating Conditions.*

Wind turbines traditionally operate as "greedy individuals", but more and more research now explore possibilities of controlling wind turbines to improve performance of entire wind farms. Two main approaches have usually been investigated, namely induction based control and wake steering control. The former aims to decrease the wake deficit, whereas the latter aims to improve the performance of subsequent turbines by deflecting the wake away from the next turbine. The wake dynamics are investigated for different control scenarios to elucidate on how and why the performance of the next turbines could potentially improve. The wind turbine and its wake is modelled using EllipSys3D(Michelsen, 1992, and Sørensen, 1995), where large eddy simulation is fully coupled to the aero-elastic tool, Flex5(Øye, 1996) through the actuator line method(Sørensen and Shen, 2002). Various statistical measures as well as proper orthogonal decomposition(POD) is used to analyse the dynamics and large coherent structures of the turbulent wakes.