Vertical-Axis Wind Turbine Start-Up Modelled with a High-Order Numerical Solver

Vertical axis wind turbine (VAWT) start-up is a highly non-linear process, with turbines experiencing a long idling period of low acceleration before a sudden increase in rotational velocity to a final equilibrium state. The physics of start-up behaviour is not well understood, with some analyses showing VAWTs to be incapable of self-start, in spite of experimental and field evidence to the contrary. This study attempts to assess the impact of blade-wake interactions on start-up behaviour. A high-order discontinuous Galerkin (DG) solver was used to simulate the flow around a VAWT, with experimentally obtained acceleration applied to the turbine, forcing it from standing to a tip-speed ratio (TSR) of 2 in a typically non-linear pattern. Additionally, the DG code was run with a constant TSR of 1, a TSR at which blade-wake interactions are known to occur. A blade-element momentum (BEM) method was used to provide an additional simulation of the turbine at this speed. Since the DG code captures blade-wake interactions while the BEM does not, a comparison of the outputs of the two was made to assess the impact of the interactions on blade forces.