Experimental Assessment of an Actuator-Line Simulation Tool for VAWTs

The paper presents the detailed experimental assessment of an intermediate-fidelity computational model for the resolution of the flow around Vertical Axis Wind Turbine (VAWT) rotors. This technique, which treats the blade aerodynamics using an actuator-line (ACL) representation, allows largely limiting the computational effort normally associated to 3D calculations, thus providing the ideal framework for simulating wind turbines immersed within the atmospheric boundary layer or operating in the urban environment. The highly unsteady and fully three-dimensional character of VAWT aerodynamics complicates the model implementation and makes it prone to reliability issues; for this reason, experimental validation is decisive for evaluating the reliability of the simulation tool, and for investigating the impact of the various corrective sub-models implemented. In this paper, such procedure is carried out by comparing the ACL prediction with the data coming from an extensive wind tunnel characterization of a real-scale model of a H-shaped VAWT for micro-generation, for which both performance and detailed wake measurements are available. The comparison is made for different tip-speed ratio conditions and combinations of sub-models in the ACL tool. Results show that the turbine performance and the main features of the rotor aerodynamics are well reproduced by the model, resulting in a very good prediction of the wake profile in the equatorial section of the turbine. The quantitative agreement between experiments and calculations locally drops close to the blade tip, where the flow field is fully dominated by 3D effects, even though the model is still able to reproduce qualitatively the most relevant wake features.