Performance analysis of low Reynolds number vertical axis wind turbines using low-fidelity and mid-fidelity methods and wind conditions in the city of Nottingham

The aerodynamics of small-scale Darrieus vertical axis wind turbines (VAWT) is investigated at chord-based Reynolds number between 1 x 105 and 1 x 106. Initially, wind resource assessment is done for two locations in Nottingham, UK for 4 years. Both locations experience highly unsteady wind and the average wind speed is lower for the location within the city than outside the city. Next, two analytical aerodynamic methods are compared: low-fidelity Double Multiple Streamtube and mid-fidelity Lifting Line Free Vortex Wake methods. Five 3D design parameters are investigated: number of blades, blade shape, chord length, blade height and blade pitch angle. Overall, the power coefficient values and trends agree well between the two methods. The differences arise either in cases of very low solidity or high solidity. The unsteady flow field is visualized for each case using instantaneous vortices and streamwise velocity contours in the wake. The aim of the current work is twofold. Firstly, to investigate the difference between the two methods based on the physical principles modeled by each method. The second aim is to have a better understanding of the VAWT flow physics by studying the complex 3D force and flow field, and fluid dynamic interactions in the VAWT wake.