Aerodynamic analysis of complex flapping motions based on free-flight biological data

Area of Science:

• Aerospace Engineering
• Biomechanics
• Fluid Dynamics

Background:

• Bird wings utilize complex morphing mechanisms for aerial maneuvers, described by flapping, bending, folding, sweeping, and twisting.
• The aerodynamic impact of these coupled wing motions across different flight phases is not fully understood, limiting biomimetic aircraft design.

Purpose of the Study:

• To numerically investigate the effects of four flapping-based coupled wing motions (flap-bending, flap-folding, flap-sweeping, flap-twisting) on aerodynamic performance.
• To analyze these motions during distinct flight phases: take-off, level flight, and landing.
• To provide insights for designing bionic flapping-wing aircraft with multi-degree-of-freedom wings.

Main Methods:

• Utilized computational fluid dynamic (CFD) simulations on a pigeon-like airfoil model.
• Analyzed wingbeat motion data from real flying pigeons for four coupled motions.
• Examined the effects on flow field, transient aerodynamic forces, and work done by each motion.

Main Results:

• Flap-bending causes angle of attack variations, influencing leading-edge vortex (LEV) attachment and lift.
• Flap-folding regulates LEV attachment and vortex detachment, significantly impacting lift generation.
• Flap-sweeping showed minimal influence on the flow field across flight phases.
• Flap-twisting enables dynamic aerodynamic adjustments, reducing drag during take-off and increasing it during landing.

Conclusions:

• Coupled wing motions significantly affect aerodynamic performance and lift generation in birds.
• Flap-bending, flap-folding, and flap-twisting offer distinct aerodynamic control mechanisms.
• Understanding these coupled motions provides crucial theoretical guidance for developing advanced biomimetic aircraft.