Micro H-Darrieus wind turbines: CFD modeling and experimental validation

The scientific interest toward micro wind turbine power generation is growing thanks to the fact that these systems appear to be very suitable for small stand-alone devices such as controllers, actuators, sensors, small lightning systems which cannot be easily powered through electricity grids. Furthermore, micro wind turbines are widely used for wind tunnel testing as the wind tunnel dimensions are usually quite limited. The present paper deals with the CFD modeling of a micro H-Darrieus wind turbine, designed and tested in the subsonic wind tunnel, owned by the University of Catania. Such small rotors are usually very difficult to simulate accurately due to the very low Reynolds number effects and the strong unsteadiness related to their operation. Through the use of an accurate unsteady Delayed Detached Eddy Simulation approach for turbulence modeling, the authors demonstrated the possibility to obtain reliable CFD 2D model of such micro rotors. The modeling methodology was developed by means of an accurate grid and time step sensitivity study and by comparing different approaches for turbulence closure. The model was validated using data obtained from experiments carried out in the wind tunnel, which showed a rather satisfactory predictive capability of the model. Therefore, the proposed numerical model allowed for a better comprehension of the fluid dynamic behavior of such micro rotors. Furthermore, the model will be used for trying to optimize micro H-Darrieus turbines which usually show poor efficiency compared to micro horizontal axis wind turbines.