Improving the performance of wind turbines in urban environment by integrating the action of a diffuser with the aerodynamics of the rooftops

We investigated the effectiveness of combining the concentration effects generated by a dual-pitched roof and a diffuser-shaped wall mounted over a Darrieus turbine, which is rooftop mounted with horizontal shaft running close to the roof ridge. A2D CFD study was carried out in three steps: (1) we predicted the turbine basic performance with and without a convergent-divergent diffuser in a infinite and undisturbed domain; (2) the behavior of the concentration system on the rooftop were simulated in a simplified urban contest; (3) we improved both the operating conditions and the domain geometry to make them more similar to realistic urban environments. The simulations are performed by means a fully URANS since both the turbine aerodynamic forces and the urban wind field are simulated. Results show that by integrating the actions of rooftop and diffuser a significant power increasing is obtained in skewed winds. Moreover, the diffuser allows a drastic abatement of torque fluctuations.