15th European Conference on Turbomachinery Fluid dynamics & Thermodynamics

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Main Topic:

Wind Turbines



Nicoletta Franchina  - Università degli Studi di Bergamo, Dipartimento di Ingegneria e Scienze Applicate, Italy
Otman Kouaissah - Università degli Studi di Bergamo, Dipartimento di Ingegneria e Scienze Applicate, Italy
Giovanna Barigozzi - Università degli Studi di Bergamo, Dipartimento di Ingegneria e Scienze Applicate, Italy
Giacomo Persico - Politecnico di Milano, Dipartimento di Energia, Italy


The challenging targets set by the United Nations and the European Commission to mitigate climate change demand for a radical development of innovative technologies. Wind energy is, in terms of growth, one of the most promising renewable sources, provided that offshore installations reduce their levelized cost of energy and become widespread. Only lift-driven wind turbines, either horizontal (HAWT) or vertical (VAWT) are capable to meet this goal. In this work, the latter class is considered, since it is either suited for community-scale distributed applications in urban sites as well as for utility-scale applications in offshore wind farms, in particular for floating installations. As a matter of fact, VAWTs are not prone to the large overturning moments experienced by offshore HAWT on floating platforms, as the heavy components can all be sited at the base of the turbine. Moreover, VAWT performance is less affected than HAWT one to the periodic oscillation of relative wind caused by the motion of the platform. For these reasons, VAWTs can be competitive against HAWTs in the emerging floating offshore market; however, VAWTs are also characterized by a complex aerodynamics: inherent rotor unsteadiness, periodic operation of airfoils in post-stall and deep-stall conditions, fatigue load even in uniform wind. Detailed aerodynamic investigations are therefore necessary to understand the machine operation, maximize the rotor performance, and characterize the complex vortical structures developing within and behind the rotor. In this paper, we present a computational investigation of the aerodynamics and performance of different kind of VAWTs, considering and comparing a straight-blade “H-shaped” rotor with a Troposkein “egg-beater” one, and by considering different airfoil sections. Simulations are performed by resorting to fully 3D and unsteady Computational Fluid Dynamics, by considering the URANS formulation of the equation and relying upon the Spalart- Allmaras and the SST turbulence models; the computational model was assessed via systematic comparison against experimental data coming from corresponding wind-tunnel models of selected rotors. The performance of the selected wind turbine configurations are investigated at peak efficiency condition and at high load condition, both in terms of power coefficient and of near-wake development; the computed flow fields are employed to highlight the impact of rotor and airfoil design on the machine performance and wake development, so to derive engineering implications for the optimization of vertical axis rotors.


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