The Dynamic Coupling Between the Pulse Wake Mixing Strategy and Floating Wind Turbines

In recent years control techniques such as dynamic induction control (often referred to as "The Pulse'') have shown great potential in increasing wake mixing with the goal of minimizing turbine-to-turbine interaction within a wind farm. Dynamic induction control disturbs the wake by varying the thrust of the turbine over time, which results in a time-varying induction zone. If applied to a floating wind turbine, this time-varying thrust force will, besides changing the wake, change the motion of the platform. This work investigates if the coupling between the Pulse and floater dynamics has an impact on the wake mixing performance of the Pulse. This is done by considering first the magnitude of motions of the floating wind turbine due to the application of a time-varying thrust force and secondly the effect of these motions on the wake mixing. A frequency response experiment shows that the movement of the floating turbine is heavily frequency-dependent, as is the thrust force. Time domain simulations, using a free wake vortex method with uniform inflow, show that the expected gain in average wind speed at a distance of five rotor diameters downstream is more sensitive to the excitation frequency compared to a bottom-fixed turbine with the same Pulse applied. This is due to the fact that platform motion decreases the thrust force variation and thus reduces the onset of wake mixing.