Gust response alleviation via wingtip bending freely with fluid-structure interaction approach based on dynamic modal rotation method

This paper presents a flexible wingtip bending freely for alleviating large amplitude gust loads at low Reynolds numbers. The Modal Rotation Method (MRM) is extended to a form capable of solving nonlinear structural dynamics by time discretization and iterative solving. By integrating the dynamic MRM with Computational Fluid Dynamics (CFD), this paper presents a parallelized Fluid-Structure Interaction (FSI) approach to depict the large gust encounter of the wingtip's freely bending. The numerical results of the proposed method are in great agreement with experimental data, while achieving a 63% reduction in computation time compared to a direct CFD/CSD coupling approach. The effects of bending stiffness and mass ratio of the wingtip on gust response under 1-cos gust conditions are investigated. The results show that the gust-induced lift decreases by over 15% when mass ratio is reduced to 0.027 and stiffness ratio is reduced to 0.004 under Gust Ratios (GR) of 0.5 and 1. The velocity generated by the wingtip is essential to alleviate gust. The flow field results show that under large amplitude gust conditions, the wingtip bending freely reduces the intensity of the leading-edge vortex, thus alleviating the wing's lift. In addition, it is verified that the wingtip bending freely reduces lift by over 10% for sinusoidal gusts in the frequency range of 2–7 Hz at GR of 0.5. The phase of wingtip bending is a key parameter in sinusoidal gust alleviation, with better alleviation effects observed when it is close to π/2.