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.
Highlights
The continuous growth of global energy consumption has imposed great challenges on energy supply.In recent years, wind energy has been playing a vital role in providing clean and renewable energy to fulfil demands without generating major adverse impact on the environment like other conventional energy sources based on fossil fuels [1]
Because swell waves have a well-organized long-crest shape and can induce strong distortion to the wind field near the wave surface, in this study we applied the phase-average method to quantify the statistics of the turbulent flows and identify their correlation with the swell-wave phase
Because we configured the simulations to have an equal spacing of three swell wavelengths between each turbine row, we could further average ensemble average h f i0 among each turbine to get final-phase averaged quantity h f i( x, y, z; θl ) =
Summary
The continuous growth of global energy consumption has imposed great challenges on energy supply. Performed pioneering studies using LES and ADM to simulate complex turbulent-flow physics, vertical kinetic-energy entrainments, and scalar transport in fully developed wind-turbine array boundary layer. Yang et al [7,9] coupled LES with a wave simulation based on the high-order spectral method (HOSM), and studied the effect of wind sea as well as swell waves on flow structures and turbulence in offshore wind farms with fixed turbines. We use the LES–HOSM model of Yang et al [7,9] to study the effect of swell-induced pitch motion on turbulence statistics and wind-power extraction rate in an array of floating wind turbines.
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