The aerodynamics generated by a small small-scale vertical axis wind turbine (VAWT) are illustrated in detail as a NACA0022 rotor blade carries out a complete rotation at three tip speed ratios. These aerodynamic details are then linked to the wind turbine performance. This is achieved by using detailed experimental measurements of performance and near blade PIV and also using a 2D RANS based CFD model. Uniquely therefore, the CFD model is validated against both PIV visualisations and performance measurements. At low tip speed ratios (TSR = 2), the flow field is dominated by large scale stalling behaviour as shown in both the experimental results and simulations. The onset of stall appears to be different between the experiment and simulation, with the simulation showing a gradual separation progressing forwards from the trailing edge, while the experiment shows a more sudden leading edge roll-up. Overall, similar scales of vortices are shed at a similar rate in both. The most significant CFD-PIV differences are observed in predicting flow reattachment. At a higher tip speed ratio (TSR = 3), the flow separates slightly later than in the previous condition and as occurs in the lower tip speed ratio, the main differences between the experiment and the simulation are in the flow reattachment process, specifically that the simulations predicts a delay in the process. At a tip speed ratio of 4, smaller predicted flow separation in the latter stages of the upwind part of the rotation is the main difference in comparison to the experiment.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)