Abstract
Due to abundant wind resources and land saving, offshore wind farms have been vigorously developed worldwide. The wake of wind turbines is an important topic of offshore wind farms, in which the wake expansion is a key issue for the wake model and the layout optimization of a wind farm. The large eddy simulation (LES) is utilized to investigate various offshore wind farms under different operating conditions. The numerical results indicate that it is more accurate to calculate the wake growth rate using the streamwise turbulence intensity or the total turbulence intensity in the environment. By fitting the results of the LES, two formulae are proposed to calculate the wake growth rate of the upstream wind turbine. The wake expansion of the downstream wind turbine is analyzed, and the method of calculating the wake growth rate is introduced. The simulation indicates that the wake expansion of the further downstream wind turbines is significantly reduced. The smaller lateral distance of wind turbines in the offshore wind farm has the less wake expansion of the wind turbines. The wake expansion under different inflow wind speeds is also analyzed, while the wake expansion of wind turbines under more complex conditions needs to be further studied.
Highlights
Wind energy as a kind of renewable energy has been increasingly developed in many countries in the recent years
The solver used in the present work is the Simulator for Wind Farm Applications (SOWFA), which is developed by the National Renewable Energy Laboratory (NREL) [16,27], Colorado, USA
The large eddy simulation (LES) technique is used to simulate a series of offshore wind farms
Summary
Wind energy as a kind of renewable energy has been increasingly developed in many countries in the recent years. Troldborg et al [7] used the LES to research the wake of wind turbines and obtained the effect of inflow turbulence on the wake. In the analytical wake model, it is difficult to accurately express the wake growth rate in theory, which can be obtained by fitting high-fidelity LES data. The earlier studies have fitted the formulas of wake growth rate based on a single wind turbine with a fixed inflow wind velocity. Based on the simulation results, the effect of different turbulence intensities on the wake growth rate is analyzed in the offshore wind farms. Two formulae of the wake growth rate are proposed by fitting the LES data, which are subsequently examined in the offshore wind farm and compared with the formulae introduced in earlier works.
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