16. Visualising Dynamic Stall Around a Vertical Axis Wind Turbine Blade Through Particle Image Velocimetry

The vertical axis wind turbine aerodynamics are highly complex and unsteady. Inherent in the operation of VAWTs is the presence of the dynamic stall phenomenon that has a major influence in the overall performance of the rotor. The acquisition of a reliable experimental flow field data set presents a means to increase the level of understanding of VAWT performance and flow physics through visualisations. The method developed in this study includes the setup of the PIV system in the wind tunnel, surface treatment of the VAWT blades, verification of test settings, and image processing and data analysis. The measurement of the flow fields around a VAWT blade at tip speed ratios of λ = 2.5 and 4 were carried out and the results show significant differences in the stalling characteristics between different λ with increased occurrence of deep and prolonged separation of flow from the blade surface at lower λ. In both cases, however, dynamic stall is observed. The data acquired is an invaluable reference for VAWT flow physics as well as validation of numerical models such as CFD.