Idealized simulations of wind farm interactions with intermittent turbulence in stable boundary layer conditions

Abstract

Abstract. Stable atmospheric boundary layer conditions typically correspond to low turbulence levels, but intermittent periods of elevated turbulence can occur during otherwise quiescent conditions. The interaction between intermittent turbulence and wind turbines is not well understood because of sparse observations, as well as the difficulty in realistically resolving small-scale turbulence during strongly stable conditions with numerical simulations. In this study, an explicit filtering and reconstruction approach for large-eddy simulation (LES) is used to simulate weakly and strongly stable conditions, with surface cooling rates of −0.2 and −2.0 K h−1, respectively. This approach can sustain resolved background turbulence at relatively coarse grid spacing and stronger stratification compared to conventional closures, resulting in more realistic intermittent stable boundary layer (SBL) turbulence. The idealized LES capability of the Weather Research and Forecasting model is employed with turbine rotors parameterized using generalized actuator disks to 1) determine how the presence of turbine wakes affects SBL evolution, and 2) examine the effect of intermittent turbulence on power production and wake recovery. Wakes increase mixing and therefore increase the height of the SBL, with this effect becoming more prominent as SBL strength increases. Intermittent turbulence does not have a significant impact on mean power generation and wake recovery because the relevant turbulent structures in this study only affect the bottom half of the rotor disk. Power production is, however, more variable during periods of elevated turbulence, demonstrating the impact of SBL intermittency. This study uses an idealized configuration, focusing on LES model performance and physical understanding, with the goal of informing future simulations of the conditions observed during the American Wake Experiment.

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