Aerodynamics, Scaling, and Performance of a Flexible Flapping Wing.

Aerodynamics of Flexible Wings;Computational Fluid Dynamics;Fluid-structure Interaction;Micro-air-Vehicles;Aerospace Engineering;Engineering;Aerospace Engineering

Kang, Chang-KwonYoung, Yin Lu ;

University of Michigan

关键词: Aerodynamics of Flexible Wings;    Computational Fluid Dynamics;    Fluid-structure Interaction;    Micro-air-Vehicles;    Aerospace Engineering;    Engineering;    Aerospace Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/86519/kangck_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Effects of flexibility on the force generation and the propulsive efficiency of flapping flexible wings are elucidated. First, based on a control volume analysis around a moving body immersed in viscous fluid, different types of forces, as a function of the Reynolds number, reduced frequency, and Strouhal number, acting on the moving body are identified based on a scaling argument. i) At the Reynolds number regime of O(104) and reduced frequency of 0.25 the vortex force term is the most dominant: for a thin rigid flat-plate massive leading-edge separation is observed due to its sharp leading-edge under a combined pitch-plunge kinematics. This geometric effect is seen to dominate over the viscosity effects, such that the Reynolds number dependence on both the flow field and the lift is small. Compared to a SD7003 airfoil with blunter leading-edge, small radius of curvature in the leading-edge of the flat-plate leads to an earlier and stronger leading-edge vortex, which enhances the resulting lift; ii) At the Reynolds number regime of O(103 – 104) and the reduced frequency of O(1), the added mass forces, which are proportional to the acceleration of the wing, are dominant. In this parameter space, chordwise, spanwise, and isotropic flexibilities are considered to identify the dominant mechanisms in the force generation and propulsive efficiency of flapping wings. By modeling the wing as a linear beam, a relationship between the propulsive force and the maximum relative wing tip deformation is established by considering the energy balance of the wing: The lift generation of insect flyers, approximated by its weight, largely follows the same scaling relationship. Furthermore, a scaling for the propulsive efficiency is found. The current study predicts that the maximum propulsive force is obtained when the motion is near the resonance, whereas the optimal propulsive efficiency is reached when the wing flaps at about half of the natural frequency, consistent with the results reported in the literature. The resulting scaling parameter, given as a combination of a priori known wing geometry, structural and fluid properties, and motion kinematics, helps to gain more insight in the combined fluid and structural dynamics.