PIV measurements and CFD simulation of the performance and flow physics and of a small-scale vertical axis wind turbine

The aerodynamics generated by a small small-scale vertical axis wind turbine 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 particle image velocimetry (PIV) and also by using a two-dimensional Reynolds-averaged Navier-Stokes-based computational fluid dynamics (CFD) model. Uniquely, therefore, the CFD model is validated against both PIV visualizations and performance measurements. At low tip speed ratios (=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 forward 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 experimental results and simulations. The most significant CFD-PIV differences are observed in predicting flow re-attachment. At a higher tip speed ratio (=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 re-attachment 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. Copyright (c) 2013 John Wiley & Sons, Ltd.