Virtual incidence effect on rotating airfoils in Darrieus wind turbines. (1st March 2016)

• Record Type: Journal Article
• Authors: Bianchini, Alessandro; Balduzzi, Francesco; Ferrara, Giovanni; Ferrari, Lorenzo
• Is Part Of: Energy conversion and management. Volume 111(2016)
• Page Start: 329
• Page End: 338
• Publication Date: 2016-03-01
• Subjects: Darrieus -- Vertical axis wind turbine -- Flow curvature -- Virtual incidence -- CFD -- Angle of attack -- BEM; Direct energy conversion -- Periodicals; Energy storage -- Periodicals; Energy transfer -- Periodicals; Énergie -- Conversion directe -- Périodiques; Direct energy conversion; Periodicals; 621.3105
• DOI: 10.1016/j.enconman.2015.12.056
• Languages: English
• ISSNs: 0196-8904

Abstract

Abstract : Graphical abstract: Highlights: Novel methods to reduce CFD results into 1D aerodynamic parameters. Assessment of the virtual incidence (VI) effect on Darrieus VAWT blades. It is shown that blades experience a virtual AoA variation with respect to theoretical expectations. Real AoAs are calculated for different airfoils in motion and compared to BEM predictions. Abstract: Small Darrieus wind turbines are one of the most interesting emerging technologies in the renewable energies scenario, even if they still are characterized by lower efficiencies than those of conventional horizontal-axis wind turbines due to the more complex aerodynamics involved in their functioning. In case of small rotors, in which the chord-to-radius ratios are generally high not to limit the blade Reynolds number, the performance of turbine blades has been suggested to be moreover influenced by the so-called "flow curvature effects". Recent works have indeed shown that the curved flowpath encountered by the blades makes them work like virtually cambered airfoils in a rectilinear flow. In the present study, focus is instead given to a further effect that is generated in reason of the curved streamline incoming on the blades, i.e. an extra-incidence seen by the airfoil, generally referred to as "virtual incidence". In detail, a novel computational method to define the incidence angle has been applied to unsteady CFD simulations of three airfoils in a Darrieus-like motion and their effective angles of attack have been compared to theoretical expectations. The analysis confirmed the presence of an additional virtual incidence on the airfoils and quantified it for different airfoils, chord-to-radius ratios and tip-speed ratios. A comparative discussion on BEM prediction capabilities is finally reported in the study.