Lift Recovery in Post-Stall Region

Accurate prediction of airfoil performance through stall underpins the successful design of modern proprotors and wind turbines, which can exhibit significantly stalled flow during normal operation. Existing stall models typically employ two-region approaches: coupling pre-stall data with semi-empirical deep-stall models. None of the current low-order methods accurately captures the initial drop and recovery of lift in the post-stall regime. This paper proposes a novel three-region lift model, which accurately predicts the regions of stall, recovery, and deep-stall across a range of airfoils and Reynolds numbers. This is achieved through the inclusion of a semi-empirical implementation of Rayleigh’s flat plate theory. The model is directly compared against published alternatives and integrated into a low-order solver. The inclusion of the new model results in thrust prediction improvements across the operational range when compared to current two-region approaches of 7% for a small-scale rotor. It is also shown to be up to 74% more accurate in the initial drop and recovery regions than other published methods for an isolated airfoil. In all scenarios, the model is shown to produce a more physical representation of an airfoil through stall, which has great potential for improving the fidelity of performance, structural, and acoustic simulations.