A Model to Account for the Virtual Camber Effect in the Performance Prediction of an H-Darrieus VAWT Using the Momentum Models

Abstract

This study reports an investigation on the influence of the virtual camber effect on the performance prediction of an H-Darrieus VAWT using a theoretical approach based on the Momentum Models. In detail, a simplified model is proposed which highlights a limit point below which the virtual camber effect must be neglected to correctly evaluate the performance of the airfoils. This correction provides a more accurate description of the unstable region of the power curve, for which very few in-depth studies are available. An accurate description of the left side of the power curve is, however, of particular importance for a correct prediction of the self-starting capabilities of the rotor, which are presently considered as a decisive requirement for small-power machines. On this basis, the effects of the new virtual camber estimation on the transient study of an H-Darrieus rotor are also presented here. This has been carried out by means of a specifically developed numerical code. All the theoretical conjectures and the numerical models have been validated with the experimental data of two wind-tunnel campaigns on two different models of H-Darrieus turbine.