Vertical axis wind turbines (VAWTs), such as the lift-driven H-Darrieus turbine, are widespread renewable energy devices for generating electricity in the built environment, where their insensitivity to the wind direction is a particularly attractive feature. These machines are also being considered for larger, utility-scale applications. Vertical axis turbines are also being developed and tested for tidal power applications. In all these cases, the aero- or hydromechanical design of vertical axis rotors requires a very accurate prediction of their formidably complex unsteady fluid mechanics. The prediction of such flows based on research and commercial Navier-Stokes Computational Fluid Dynamics software and aiming at substantially improving VAWT design technologies is an activity we are strongly engaged with in collaboration with the Department of Industrial Engineering at the University of Florence.
The two figures below report views of a typical structured multi-block computational grid used for the analysis of the flow field of a 3-blade Darrieus turbine. The figure on the left refers to the rotor area and that on the right is an enlarged view of the grid around one of the blades. The grid reported in both figures has been coarsened to enhance graphical clarity.
The grid depicted above has been used to obtain the vorticity contours reported below, which highlight a significant level of interaction between the blades and their wakes. The same grid has been used to solve this unsteady flowfield using our Navier-Stokes research code COSA (left) and the commercial package FLUENT. An excellent agreement of the two predictions is observed.