Large-Eddy Simulation-Based Study of Effect of Swell-Induced Pitch Motion on Wake-Flow Statistics and Power Extraction of Offshore Wind Turbines

Abstract

In this study, the effects of ocean swell waves and swell-induced pitch motion on the wake-flow statistics and power extraction of floating wind turbines are numerically investigated. A hybrid numerical model coupling wind large-eddy (LES) and high-order spectral-wave simulations is employed to capture the effects of ocean swell waves on offshore wind. In the simulation, 3 × 3 floating wind turbines with prescribed pitch motions were modeled using the actuator disk model. The turbulence statistics and wind-power extraction rate for the floating turbines are quantified and compared to a reference case with fixed turbines. Statistical analysis based on the phase-average approach shows significant swell-correlated wind-velocity variations in both cases, and the swell-induced pitch motion of floating turbines is found to cause oscillations of wind-turbulence intensity and Reynolds stress, as well as an increase of vertical velocity variance in the near-wake region. Swells also cause periodic oscillation in extracted power density in the fixed turbine case, and the turbine pitch motion in the floating turbine case could further modulate this oscillation by shifting the phase dependence by about 180 degrees with respect to the swell-wave phase.

Keywords

• offshore wind farm
• large-eddy simulation
• swell waves
• wind–wave interaction
• pitch motion effect