Measurement-Driven Large-Eddy Simulations of a Diurnal Cycle during a Wake Steering Field Campaign

Abstract. High-fidelity flow modeling with data assimilation enables accurate representation of the wind-farm operating environment under realistic, nonstationary atmospheric conditions. Capturing the temporal evolution of the turbulent atmospheric boundary layer is critical to understanding the behavior of wind turbines under operating conditions with simultaneously varying inflow and controls inputs. This paper covers the identification of a case study during a field evaluation of wake steering; the development of a tailored mesoscale-to-microscale coupling strategy that captured local flow conditions within a large-eddy simulation (LES), given observations that do not completely describe the wind and temperature fields throughout the simulation domain; and the application of this coupling strategy to validate high-fidelity aeroelastic predictions of turbine performance and wake interactions with and without wake steering. The case study spans 4.5 hours after midnight local time, during which wake steering was toggled on and off five times, achieving yaw offset angles ranging from 0° to 17°. To resolve these nonstationary nighttime conditions, the turbulence field was evolved starting from the diurnal cycle of the previous day. Given these simulated background conditions, an LES with actuator-disk turbines was compared to a steady-state engineering wake model, demonstrating agreement with measurements under partially and nearly waked conditions. The LES was also able to capture conditions during which an upstream turbine wake induced a speedup at a downstream turbine and increased power production by 10 %.