*Article* **Aerodynamic Performance of VAWT Airfoils: Comparison between Wind Tunnel Testing Using a New Three-Component Strain Gauge Balance and CFD Modelling**

**Luis Santamaría, Mónica Galdo Vega, Adrián Pandal, José González Pérez, Sandra Velarde-Suárez and Jesús Manuel Fernández Oro \***

> Fluid Mechanics Area, Department of Energy, University of Oviedo, C/Wifredo Ricart s/n, 33204 Gijon, Asturias, Spain

**\*** Correspondence: jesusfo@uniovi.es

**Abstract:** Vertical axis wind turbines are an emerging and in-development wind energy technology which are characterized by their complicated aerodynamics. Detached flow conditions, which are typically developed at operational tip speed ratios, demand a rigorous characterization of the airfoils for an accurate prediction of the turbine performance. In this work, a custom-built, threecomponent external strain gauge balance, specifically developed for airfoil testing, is validated. The physical reasons responsible for discrepancies with reference data are also analyzed. Two- and three-dimensional flat plates, as well as the DU06-W-200 airfoil, are tested in a wind tunnel. Lift and drag coefficients and pitching moments are obtained for a wide angular range at Re = 200,000. The results are compared with data from the bibliography and CFD simulations, performed with the recently developed GEKO (generalized k-omega) turbulence model, achieving remarkable agreement. Instantaneous forces are also analyzed with both experimental and CFD techniques, providing interesting results of the unsteady fluid dynamics. Finally, critical factors affecting the measurements are identified and enhancements are proposed for future works. In summary, a thorough evaluation of this new balance design is provided, showing its valuable potential for VAWT applications.

**Keywords:** airfoil testing; strain gauge balance; wind tunnel; GEKO turbulence model; vertical axis wind turbine; VAWT
