13th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
The paper presents the results of a computational study on the aerodynamics and the performance of a small-scale Vertical Axis Wind Turbine (VAWT) for distributed micro-generation. The complexity of VAWT aerodynamics, which are inherently unsteady and three-dimensional, makes high-fidelity flow models extremely demanding in terms of computational cost, limiting the analysis to mainly 2D or 2.5D Computational Fluid-Dynamic (CFD) approaches. This paper discusses how a proper setting of the flow model and of the numerical solution opens the way for carrying out fully 3D unsteady CFD simulations of a VAWT with engineering-relevant computational cost. Two operating conditions are considered, covering both peak efficiency condition as well as off-design operation. The fidelity of the numerical predictions is assessed via a systematic comparison with the experimental benchmark data available for this turbine, consisting of both performance and wake measurements carried out in the large-scale wind tunnel of the Politecnico di Milano. The analysis of the flow field on the equatorial plane allows highlighting its time-dependent evolution, with the aim of identifying both the periodic flow structures and the onset of dynamic stall. The 3D computational model allows investigating the aerodynamics of the struts and the evolution of the trailing vorticity at the tip of the blades, eventually resulting in periodic large-scale vortices.