Driving mechanism of dragonfly’s wing flapping pattern for liquid circulation inside wing

Flying animals can inspire practical approaches to a more advanced way of flying. Dragonflies demonstrate a special flapping pattern in which their wings perform torsional movement while flapping, which is different from that of birds. This flapping pattern is referred to as nonsynchronous flapping in this article. We present a hypothesis that nonsynchronous flapping provides a driving force for enhancing the haemolymph circulation inside dragonfly wings. To support this hypothesis, a controlled experiment was designed and conducted with living dragonflies. By observing the liquid motion inside the vein within free flapping wings and restricted wings of living dragonflies, this hypothesis was supported. A mathematical model of the flapping wing was built and numerically studied to further support the function of the nonsynchronous flapping pattern in driving the circulation. With these studies, a theoretical explanation for the mechanism of enhancing the haemolymph circulation by nonsynchronous flapping was provided.