The influence of Blade Chord on the Aerodynamics and Performance of Vertical Axis Wind Turbines

The climate change due to emissions from the combustion of fossil fuel to meet the ever increasing energy demands of the growing world population has roused the attention of governments and individuals to protect the environment. The formulated policies to protect the environment have aroused interest in wind turbines as an alternative source of energy. The suitability of the vertical axis wind turbines (VAWTs) in harnessing energy from the wind in the built areas have been shown, but there still exists a large knowledge gaps in the aerodynamics and performance of the VAWT especially in the design and selection of an appropriate blade chord. This thesis studied the influence of the blade chord on the aerodynamics and performance of vertical axis wind turbines through experimental and computational fluid dynamics methods. Two VAWT configurations of blade chords 0.04m (AR = 15) and 0.03m (AR = 20) with corresponding solidities of 0.34 and 0.26 were used for the investigations. The performance and the flow fields of the two configurations were measured experimentally through the use of performance measurement method and Particle Image Velocimentry (PIV) measurement techniques. All the experimental tests were conducted in a low-speed open suction wind tunnel and the results are presented. Computational fluid dynamics modelling based on the Unsteady Reynolds Average Navier-stokes (URANS) was employed to simulate the two configurations at the same wind tunnel test conditions to complement the revelations from the experimental tests. The developed CFD models after a parametric study that enabled the selection of the model’s features were validated against experimental data by comparing both forces and the flow physics. Vorticity of the CFD flow visualisation and blade forces provided an additional and penetrating insight into the aerodynamics and performance of the VAWTs by linking flow physics, and performance to the aerodynamics. The VAWT flow physics, aerodynamics and performances have been shown to depend on the Reynolds numbers that ranges from 1.27x103 to 1.1x105, the blade chord (solidity), the azimuth angle blade stall is initiated and the dynamic stall associated with the flow fields around the blade. At 6m/s test condition, the C = 0.04m VAWT attained peak CP = 0.165 at λ = 4, while the C = 0.03m VAWT performed in the negative region at all the λ. The better performance attained by the C = 0.04m VAWT over the C = 0.03m VAWT was repeated at all other wind speeds tested in the experiments and also in the computational fluid dynamics investigations. The C = 0.04m VAWT attained a higher peak CP = 0.326 at 8m/s at λ = 3.75 indicating increased performance with increases in Reynolds numbers. This trend was equally seen with the C = 0.03m VAWT in the experiments and also the computational fluid dynamics results. The VAWT with σ = 0.34 performed better than σ = 0.26 VAWT in all the conditions tested due to its higher Reynolds numbers and solidity differences that influence the nature of the dynamic stall phenomenon associated with the flow fields around the blades.