An Experimental Study of the Aerodynamics and Performance of a Vertical Axis Wind Turbine in a Confined and Unconfined Environment

TLDR

This study experimentally investigates an H‑type vertical axis wind turbine at Politecnico di Milano to evaluate its aerodynamics and performance. The turbine was tested in a large‑scale wind tunnel under both confined and unconfined conditions, with integral torque and thrust measurements and detailed aerodynamic flow field measurements to assess blockage effects. Experimental data indicate that existing blockage correlations are inadequate for VAWTs, with thrust and power curves peaking at a coefficient of ~0.28 at TSR 2.5, and flow measurements revealing a fully three‑dimensional, nonsymmetrical wake with time‑dependent tip vortices and dynamic stall at TSR < 2.

Abstract

This paper presents the results of a wide experimental study on an H-type vertical axis wind turbine (VAWT) carried out at the Politecnico di Milano. The experiments were carried out in a large-scale wind tunnel, where wind turbines for microgeneration can be tested in real-scale conditions. Integral torque and thrust measurements were performed, as well as detailed aerodynamic measurements to characterize the flow field generated by the turbine downstream of the rotor. The machine was tested in both a confined (closed chamber) and unconfined (open chamber) environment, to highlight the effect of wind tunnel blockage on the aerodynamics and performance of the VAWT under investigation. The experimental results, compared with the blockage correlations presently available, suggest that specific correction models should be developed for VAWTs. The experimental thrust and power curves of the turbine, derived from integral measurements, exhibit the expected trends with a peak power coefficient of about 0.28 at tip-speed ratio equal to 2.5. Flow measurements, performed in three conditions for tip speed ratio equal to 1.5, 2.5, and 3.5, show the fully three-dimensional character of the wake, especially in the tip region where a nonsymmetrical wake and tip vortex are found. The unsteady evolution of the velocity and turbulence fields further highlights the effect of aerodynamic loading on the wake unsteadiness, showing the time-dependent nature of the tip vortex and the onset of dynamic stall for tip speed ratio lower than 2.