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

High-Altitude-Long-Endurance (HALE) Unmanned Aerial Vehicles (UAV) operating at low Reynolds numbers face significant challenges from atmospheric gusts, which can intensify flow separation and induce critical structural loads. Conventional gust alleviation techniques using control surfaces have limitations under high-amplitude gusts at transitional Reynolds numbers. Existing fluid-structure interaction (FSI) methods struggle to efficiently capture both nonlinear aerodynamics and large structural deformations during severe gust encounters.

In a recent study published in the Chinese Journal of Aeronautics (https://doi.org/10.1016/j.cja.2025.103851), Dr. Yang Zheng, Prof. Yuting Dai, and colleagues from Beihang University proposed a novel approach using passively bending flexible wingtips to mitigate gust loads. This method leverages fluid-structure interaction through an advanced computational framework.

"The core innovation lies in extending the Modal Rotation Method to dynamic simulations," explained Prof. Dai. "This allows us to efficiently model large nonlinear deformations while capturing changes in load distribution during gust events." The wingtip, designed to bend freely under aerodynamic loads, consists of a lightweight flexible segment replacing the conventional rigid tip. Crucially, this system requires no active control mechanisms or additional energy input.

The team developed a parallelized FSI solver integrating their dynamic Modal Rotation Method (MRM) with Computational Fluid Dynamics (CFD). They established a theoretical framework relating gust alleviation performance to wingtip parameters like bending stiffness ratio and mass ratio. Numerical validation against wind tunnel experiments showed excellent agreement. Remarkably, their method achieved a 63% reduction in computation time compared to conventional CFD/CSD coupling while maintaining accuracy.

Key findings demonstrate significant performance benefits:

*Over 15% reduction in peak lift coefficient under 1-cos gusts (Gust Ratio=0.5) when reducing wingtip mass ratio to 0.027 and stiffness ratio to 0.004.

*17% lift reduction and 26% wing-root bending moment alleviation under severe gusts (Gust Ratio=1).

*25% sinusoidal gust lift reduction achieved at 3 Hz gust frequency, with effectiveness maintained across 2-7 Hz.

*Flow analysis revealed the mechanism: Wingtip bending generates upward velocity at peak lift, suppressing leading-edge vortex intensity and reducing effective angle of attack. Phase alignment near π/2 between gust peak and wingtip motion proved critical for optimal damping.

"Our integrated FSI approach verifies both the feasibility and significant performance gains of freely bending wingtips," stated Dr. Zheng. "The wingtip's morphing velocity is key to disrupting detrimental vortex structures."

The authors highlight advantages including structural simplicity, passive operation, and effectiveness across diverse gust types (transient 1-cos and continuous sinusoidal). Challenges remain in optimizing material properties for real-world implementation, understanding complex vortex interactions at extreme deformations, and scaling for different aircraft configurations. "We are actively researching these aspects to mature this technology," Prof. Dai noted. They anticipate this concept will enhance the safety and efficiency of future high-altitude long-endurance UAVs operating in gusty environments.

Original Source

Yang Zheng, Yuting Dai, Guangjing Huang, Yating Hu. Gust response alleviation via wingtip bending freely with fluid-structure interaction approach based on dynamic modal rotation method [J]. Chinese Journal of Aeronautics, 2025, https://doi.org/10.1016/j.cja.2025.103851.

About Chinese Journal of Aeronautics 

Chinese Journal of Aeronautics (CJA) is an open access, peer-reviewed international journal covering all aspects of aerospace engineering, monthly published by Elsevier. The Journal reports the scientific and technological achievements and frontiers in aeronautic engineering and astronautic engineering, in both theory and practice. CJA is indexed in SCI (IF = 5.7, Q1), EI, IAA, AJ, CSA, Scopus.