Wong Jasmin C M, Joshi Vaibhav, Jaiman Rajeev K, Altshuler Douglas L
School of Civil, Aerospace, and Design Engineering, University of Bristol, Bristol BS8 1TR, UK.
Department of Mechanical Engineering, Birla Institute of Technology & Science Pilani, K K Birla Goa Campus, Zuarinagar, Goa 403726, India.
J R Soc Interface. 2025 May;22(226):20240753. doi: 10.1098/rsif.2024.0753. Epub 2025 May 7.
During flight, birds instigate remarkably large changes in wing shape, commonly termed 'wing morphing'. These changes in shape, particularly extension-flexion, have been well documented to influence the production of aerodynamic forces. However, it is unknown how wing stiffness changes as a result of the structural rearrangements needed for morphing. We address this gap in knowledge through mechanical testing of flight feathers in anaesthetized pigeons and found that while the most distal portion of the feathered wing remained unaffected, proximal areas saw an increase in out-of-plane stiffness due to wing folding. Following this, we used computational fluid-structure interaction simulations to evaluate how this morphing-coupled change in stiffness might modulate local flow patterns to affect aerodynamic performance. We found that flexible wings perform better than entirely rigid wings as an increase in near-wall vorticity delayed flow separation. Furthermore, an increase in stiffness in a folded wing during high-speed flight prevented the reduction in lift seen in more flexible cases caused by aeroelastic flutter modes destructively interfering with shed leading-edge vortices. Collectively, these results reveal that mechanical changes coupled with wing morphing can provide a speed-dependent mechanism to enhance flight performance.
在飞行过程中，鸟类会引发翅膀形状的显著变化，通常称为“翅膀变形”。这些形状变化，尤其是伸展-弯曲，已被充分证明会影响气动力的产生。然而，由于变形所需的结构重排，翅膀刚度如何变化尚不清楚。我们通过对麻醉鸽子的飞羽进行力学测试来填补这一知识空白，发现虽然带羽翅膀的最远端部分不受影响，但由于翅膀折叠，近端区域的面外刚度增加。在此之后，我们使用计算流体-结构相互作用模拟来评估这种与变形相关的刚度变化如何调节局部流动模式以影响空气动力学性能。我们发现，柔性翅膀比完全刚性的翅膀表现更好，因为近壁涡度的增加延迟了流动分离。此外，在高速飞行过程中，折叠翅膀刚度的增加防止了在更柔性情况下因气动弹性颤振模式对脱落的前缘涡旋产生破坏性干扰而导致的升力降低。总的来说，这些结果表明，与翅膀变形相关的力学变化可以提供一种依赖速度的机制来提高飞行性能。
