The effect of coastal terrain on nearshore offshore wind farms: A large-eddy simulation study

Abstract

Performance of offshore wind farms built in the nearshore region will be affected by onshore terrain with higher turbulence in the flow when wind is blowing from land toward sea. Current study employs large-eddy simulation to investigate the effect of coastal terrain on the performance of large nearshore offshore wind farms. At first, two atmospheric boundary layer (ABL) simulation cases are defined to investigate the evolution of an internal boundary layer (IBL) during the sea-to-land and land-to-sea transition of the flow. The growth rate of the IBL was similar for both ABL simulation cases. However, the mean velocity-based definition of IBL heights, which essentially are the equilibrium layer, were half the height of shear stress-based IBLs. The first wind farm simulation case only considers an offshore surface, while the second case includes the region with land-to-sea transition upstream of the wind farm. Better wake recovery is observed in the case that considers the effect of onshore terrain. This is attributed to the higher inflow turbulence level, which resulted in higher entrainment of kinetic energy from the flow above. The farm-induced IBL for a land-to-sea transition case shows rapid growth for the first few turbine rows, while the offshore only case shows gradual growth. However, the difference between the two IBLs decreases with downstream distance, implying that for sufficiently long wind farms, both IBLs will converge. Total power output of the land-to-sea transition case is 17% higher than the offshore only case for the farm layout and roughness heights considered in this study.