Numerical investigation of an insect-scale flexible wing with a small amplitude flapping kinematics

Abstract

To maintain flight, insect-scale air vehicles must adapt to their low Reynolds number flight conditions and generate sufficient aerodynamic force. Researchers conducted extensive studies to explore the mechanism of high aerodynamic efficiency on such a small scale. In this paper, a centimeter-level flapping wing is used to investigate the mechanism and feasibility of whether a simple motion with a certain frequency can generate enough lift. The unsteady numerical simulations are based on the fluid structure interaction (FSI) method and dynamic mesh technology. The flapping motion is in a simple harmonic law of small amplitude with high frequency, which corresponds to the flapping wing driven by a piezoelectric actuator. The inertial and aerodynamic forces of the wing can cause chordwise torsion, thereby generating the vertical aerodynamic force. The concerned flapping frequency refers to the structural modal frequency and FSI modal frequency. According to the results, we find that under the condition that frequency ratio is 1.0, that is, when the wing flaps at the first-order structural modal frequency, the deformation degree of the wing is the highest, but it does not produce good aerodynamic performance. However, under the condition that frequency ratio is 0.822, when the wing flaps at the first-order FSI modal frequency, the aerodynamic efficiency achieve the highest and is equal to 0.273. Under the condition that frequency ratio is 0.6, that is, when the wing flaps at a frequency smaller than the first-order FSI modal frequency, the flapping wing effectively utilizes the strain energy storage and release mechanism and produces the maximum vertical coefficient which is equal to 4.86. The study shows that this flapping motion can satisfy the requirements of lift to sustain the flight on this scale.