Large eddy simulation and experimental study of the turbulence on wind turbines

In this research work, a micro horizontal axis wind turbine performance was assessed considering the upstream uniform and turbulent airflow of the rotor. The study was carried out experimentally, in an atmospheric boundary layer wind tunnel, and numerically, based on a Large Eddy Simulation model. The turbulent flow was modeled using a passive grid placed at different upstream distances from the rotor, providing different turbulence intensity values and integral length scales. The experimental results showed that the total efficiency decreased from 17.6% to 13.4% when operating in a turbulent environment. Total efficiency includes the power coefficient, as well as generator and inverter efficiencies, this is, the whole drive-train. On the other hand, numerical simulations showed that the turbulent inlet airflow enhanced the power coefficient. Unlike uniform inlet flow conditions, the eddies shedding resulted in torque fluctuations on the rotor shaft. Thus, the rotor absorbs these fluctuations to guarantee a quasi-stable rotation speed. So, the control system filters the signals to the lowest limit reducing the angular speed, as confirmed experimentally. Therefore, it is necessary to consider the whole drive-train to obtain conclusive results concerning the turbulent inflow.