An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies

Abstract

The relative importance of the wing's inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wing's elastic and fluid forces is dynamically similar to that of the actual insect, while the wing's inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wing's elastic forces and the wing's inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wing's elastic and aerodynamic forces, while it will be enhanced by the wing's inertial force.

Biomechanics and biomimetics in insect-inspired flight systems

“…A completely passive pitching of rigid wings with compliant attachment was detected when assuming the feathering motion driven by the fluid–structure interaction [31]. A passive feathering motion [32] was further observed using a dynamically scaled rigid wing model with an elastic attachment at the leading edge, and 80–90% of the deformation was found owing to the aerodynamic and elastic restoring forces with the remaining 10–20% due to the inertia.…”

Aerodynamic Ground Effect in Fruitfly Sized Insect Takeoff

“…Therefore, if the kinematics of the wings operating in ground effect is adjusted such that P ave,IGE /P ave,OGE = 100% at any time, the force ratio F z,ave,IGE /F z,ave,OGE is likely to increase. Among other factors, the feathering angle is very likely to change passively, when in ground effect, due to compliance of the wing [14,27,15]. Such effects would need further investigation.…”

Pseudoelastic mesh–moving using a general scenario of the selective mesh stiffening

“…The amplitude of θ z changes from 10° to 110°. In addition, a rotational displacement θ y about the y-axis, which corresponds to the flapping motion, was applied to the rigid body incrementally [4]. The amplitude of θ y is set as 60°.…”

“…This scenario gives better mesh quality in the mesh-moving of a rectangular domain with a structure consisting of a square and a fin undergoes large rotations. This is because the shear deformation of the element is adaptively considered.Keywords: Finite element method, Pseudoelastic mesh-moving, Interface tracking sisting of a square and a fin that undergoes large deformation [3,4].…”

“…Keywords: Finite element method, Pseudoelastic mesh-moving, Interface tracking sisting of a square and a fin that undergoes large deformation [3,4].…”