Technical modeling challenges for large idling wind turbines

Abstract

This paper presents comprehensive investigations into idling instability occurring on the IEA 15 MW reference turbine. The systematic studies are carried out by means of Blade Element Momentum (BEM) and free wake vortex (Vortexline) methods. Two state-of-the-art dynamic stall models are tested in the present investigations, namely the Beddoes-Leishman and the IAG dynamic stall models, implemented into a development version of the wind turbine design code Bladed. The studies highlight the importance of unsteady aerodynamic modeling to predict idling instabilities and emphasize the characteristics of each modeling strategy. It is demonstrated that the IAG dynamic stall model predicts a more physically reasonable idling instabilities. Furthermore, Vortexline enables the calculations of the induced velocities even under idling conditions in contrast to BEM. The combination of the Vortexline method and the IAG model is considered to provide the most reasonable turbine response. The studies will be helpful for load engineers to select appropriate modeling strategies and shed some light into future engineering modeling improvements of wind turbines.