Demonstrating that power and instantaneous loads are decoupled in a vertical-axis wind turbine



The flow in the meridian plane of a high aspect ratio vertical-axis wind turbine (VAWT) can be described as two dimensional. The wake that is generated by the VAWT in a two-dimensional flow consists of shed vorticity and is a result of the temporal variation of bound circulation on the blades, following Kelvin's theorem. The strength and location of the vorticity that is produced by the VAWT in a two-dimensional flow are thus independent of the average bound circulation on the blade. Two independent computational models—a potential flow panel model and a method that is based on the vorticity–velocity formulation of the Navier–Stokes equations—have been used to show that the VAWT can produce the same power for different azimuthal distributions of the blade aerodynamic loading. It is thus demonstrated that the instantaneous blade aerodynamic loading and the power conversion of a VAWT are decoupled. This observation has, potentially, significant impact on the design of the VAWT and reopens the research on asymmetric blade shapes in order to optimize the performance of this turbine configuration. Copyright © 2013 John Wiley & Sons, Ltd.