Aerodynamic Measurements on a Vertical Axis Wind Turbine in a Large Scale Wind Tunnel

TLDR

Vertical axis wind turbines are gaining attention as promising alternatives for small and micro generation, yet their complex fluid dynamics make aerodynamic optimization an open issue, necessitating detailed experimental analyses to inform design. This paper presents the first wide experimental investigation of vertical axis wind turbine aerodynamics and critically analyzes the models and correlations used to correct wind tunnel blockage effects. Experiments were conducted in the Politecnico di Milano large‑scale wind tunnel, testing real‑scale turbines under open and closed configurations to quantify blockage influence, measuring integral torque, thrust, and detailed aerodynamic fields, including unsteady flow and turbulent components resolved with hot‑wire techniques. Results show that existing theoretical blockage correction models are inaccurate for vertical axis turbines, and that tip aerodynamic phenomena and large‑scale unsteadiness are key to performance, with a simple flow model explaining differences from horizontal axis turbines.

Abstract

This paper presents the first results of a wide experimental investigation on the aerodynamics of a vertical axis wind turbine. Vertical axis wind turbines have recently received particular attention, as interesting alternative for small and micro generation applications. However, the complex fluid dynamic mechanisms occurring in these machines make the aerodynamic optimization of the rotors still an open issue and detailed experimental analyses are now highly recommended to convert improved flow field comprehensions into novel design techniques. The experiments were performed in the large-scale wind tunnel of the Politecnico di Milano (Italy), where real-scale wind turbines for micro generation can be tested in full similarity conditions. Open and closed wind tunnel configurations are considered in such a way to quantify the influence of model blockage for several operational conditions. Integral torque and thrust measurements, as well as detailed aerodynamic measurements were carried out to characterize the 3D flow field downstream of the turbine. The local unsteady flow field and the streamwise turbulent component, both resolved in phase with the rotor position, were derived by hot wire measurements. The paper critically analyses the models and the correlations usually applied to correct the wind tunnel blockage effects. Results highlight that the presently available theoretical correction models do not provide accurate estimates of the blockage effect in the case of vertical axis wind turbines. The tip aerodynamic phenomena, in particular, seem to play a key role for the prediction of the turbine performance; large-scale unsteadiness is observed in that region and a simple flow model is used here to explain the different flow features with respect to horizontal axis wind turbines.