Influence of platform dynamic yaw motions on wake, and subsequent impacts on downwind turbine power and loads.

Abstract

The floating foundations of FOWTs cause turbine motions that introduce new unknowns to the field of wind turbine wake estimation, that again leads to uncertainties in the load and power estimation of wake affected turbines. Recent studies have shown significant effects of floater motions on power production and emphasizes the need for the effect to be integrated into existing wind farm energy yield tools. Also, field measurements in installed FOWT wind farms have shown that there are measurable effects of the wake on floater yaw motions and mooring line loads.This paper describes a study that aims to quantify the effect of time-varying yaw misalignment, from floater motion and/or turbine yaw control, on the power production and turbine loads. 2 IEA 15 MW wind turbines supported by the UMaine VolturnUS-S semisubmersible, serves as the case study. The wind field and power production was simulated including the effect of steady and time-varying yawed inflow. The response of the downwind turbine in the waked wind field was simulated.Power production and loads for the downwind turbine in yaw cases are benchmarked against results for the downwind turbine without time varying turbine yaw and show that including the upwind turbine yaw motion resulted in higher mean power (up to 4%), but also larger power fluctuations. It also lead to larger standard deviations in the mooring line tension. These effects seem to decrease with increasing wind speeds and turbine spacing, and increase with the amplitude of yaw motion.