Abstract: A simplified geometric model of a bat wing was utilized to study its morphology and deformation, along with its aerodynamic characteristics, using computational fluid dynamics methods. A model was established with a parallelogram-shaped inner wing and a combined triangular outer wing. The wing deformations were categorized into four types:area variation, outer wing bending, chordwise cambering, and wing twisting. Two flight modes, slow and fast, were defined based on experimental data. The results demonstrate that the aerodynamic forces acting on the bat wing model in both slow and fast flight modes are similar in spatial-temporal distribution, with both lift and thrust generated during the downstroke phase. The forces during the upstroke phase are comparatively smaller. Thrust is generated entirely by the outer wing, whereas lift is generated by both the outer and the inner wings. Furthermore, it was found that slow flight achieves velocity adaptation primarily through angle-of-attack adjustments, supplemented by minor flapping frequency modulation. In contrast, fast flight relies predominantly on frequency adjustments, with fine-tuning of the angle of attack to maintain force equilibrium across different speeds. The analysis of the aerodynamic forces acting on the deforming bat wing contributes to a more profound comprehension of the mysteries of bat flight.

Key words: flapping, angle-of-attack, bat-like wing, aerodynamic force, computational fluid dynamics