Transient Rotational Modelling of a Vertical Axis Wind Turbine

Abstract

The short-term aerodynamic behaviour of a vertical axis wind turbine (VAWT) will be investigated through numerical simulation (using 3D COMSOL Multiphysics modelling). To adequately account for the unsteady nature of air around the rotating blades, a time-dependent rotational simulation needs to be employed to capture the time-varying nature of unsteady flows caused by blade rotation and the angle of attack. The incompressible Navier-Stokes equations were then solved to solve how the flow behaves throughout the entire computational domain including a cylindrical sub-domain rotating with the Arbitrary-Lagrangian-Eulerian (ALE) method. During the torque development, the angular velocity and mechanical power of the VAWT were determined to have a constant cyclical behaviour while the rotor accelerated, generating a series of rotational positions (i.e. the torque had rapidly increased and then became steady state, thus exhibiting periodic oscillations relative to the blades’ rotational positions). Velocity contours also showed significant velocity gradients at the leading edges of the blades due to wind energy extraction from the turbine, as well as development of wake structures downstream of the turbine.