The operation of a group of wind turbines operating in extreme transient wind conditions has been simulated using LES and actuator models. The wind condition models are based on the extreme coherent gust (ECG) structure from the International Wind Turbine Design Standard IEC61400-l:2005 which consists of both a gust and wind direction change simultaneously. The implementation of the models is discussed, particularly in regard to the issues encountered in adapting the models for a CFD domain. Wind turbines are modelled using the actuator sector method in a coupling framework in which the FAST aero-elastic simulation code operates within the CFD environment. This allows dynamic turbine operation with pitch and yaw control. A turbulent atmospheric boundary layer passing through three rows of turbines was simulated. The ECG was then introduced, initially as independent gust and direction change components and then as a combined wind event. The propagation of the wind event structures are analysed, along with the operation of the wind turbine array. The gust model simulations showed the transport of a high velocity region through the computational domain although some transformation of the gust profile was observed. The high velocities of the gust event trigger significant pitch actuation of the turbines. The wind shift simulations show a coherent wind shift front propagating through the domain at the free-stream wind-speed and the resulting yaw actuation of the wind turbines. Some decay of the shift front due to high levels of turbulence is also observed. Results from the ECG demonstrate the successful implementation of the combined wind event structure. The resulting flow field showed high levels of turbulent mixing as the event front propagated through the domain resulting in significant transformation of the wind signal. The simulations demonstrate the ability to model groups of turbines operating in transient wind conditions which can used study turbine loading or test turbine control strategies.
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