The Influence of Unsteady Wind on the Performance and Aerodynamics of Vertical Axis Wind Turbines

Interest in small–scale wind turbines as energy sources in the built environment has increased due to the desire of consumers in urban areas to reduce their carbon footprint. Vertical axis wind turbines (VAWTs) have shown to be potentially well suited within the urban landscape. However, there is a large gap in the fundamental understanding of VAWT operation in turbulent, unsteady wind that is typical of the built environment.

This dissertation investigates the aerodynamics and performance of VAWTs in fluctuating wind through experiments and numerical simulations. All experimental investigations utilise a low–speed open section wind tunnel. The use of a shutter mechanism that generates unsteady wind in the wind tunnel is detailed. Performance measurements for turbine power use a validated method previously developed in the same laboratory with slight modification for unsteady wind performance. Both steady and unsteady power performance tests results are presented. Near–blade flow physics during steady wind operation is scrutinised using Particle Image Velocimetry (PIV).

Complementing the findings in experiments, numerical simulations using Unsteady Reynolds Averaged Navier–Stokes Computational Fluid Dynamics (URANS CFD) are employed. The numerical model is validated using experimental data. Blade force measurements that are not available from experiments are extracted from the numerical models to provide additional insight for performance analysis. A survey of varying unsteady wind parameters is conducted to examine the effects of various unsteady wind conditions on the performance of the VAWT. The aerodynamics is inspected through vorticity visualisations alongside blade force metrics to link performance to blade stall. Results show marginal improvement on VAWT performance (CP) with small wind speed fluctuations versus steady wind CP. Operating the VAWT at tip speed ratios (λ) higher than steady wind peak CP λ also improve performance. Conditions other than the stated above reduce VAWT CP.