Wake-added turbulence characteristics and modeling in the stratified atmospheric boundary layer

To achieve decarbonization targets, wind turbines are growing in hub height, rotor diameter, and are being deployed in new locations with diverse atmospheric conditions not previously seen, such as offshore. Physics-based analytical wake models commonly used for the design and control of wind farms simplify atmospheric boundary layer (ABL) and wake physics to achieve computational efficiency. This is accomplished primarily through a simplified model form that neglects certain flow processes, such as stratification, and through the parameterization of ABL and wake turbulence through a wake spreading rate. In this study, we analyze wind turbine wakes over a range of atmospheric stabilities and ambient turbulence intensities using large eddy simulation (LES). To parse the turbulence in the wake from the turbulent, incident ABL flow, we decompose the flow into the base ABL flow and the deficit flow produced by the turbine. The subsequent deficit budget analysis allows for isolation of wake-added quantities, such as wake-added turbulence kinetic energy, which we then utilize in Reynolds-Averaged Navier Stokes (RANS) based eddy viscosity models to predict mean wake momentum. With this dataset, we analyze the primary forcing and transport mechanisms that influence wake-added turbulence in stratified ABL flow. We also evaluate the assumptions present in engineering models for wake-added turbulence through turbulence budget analysis.