Zongxian Liang

3D reconstruction and analysis of wing deformation in free-flying dragonflies

SUMMARY Insect wings demonstrate elaborate three-dimensional deformations and kinematics. These deformations are key to understanding many aspects of insect flight including aerodynamics, structural dynamics and control. In this paper, we propose a template-based subdivision surface reconstruction method that is capable of reconstructing the wing deformations and kinematics of free-flying insects based on the output of a high-speed camera system. The reconstruction method makes no rigid wing assumptions and allows for an arbitrary arrangement of marker points on the interior and edges of each wing. The resulting wing surfaces are projected back into image space and compared with expert segmentations to validate reconstruction accuracy. A least squares plane is then proposed as a universal reference to aid in making repeatable measurements of the reconstructed wing deformations. Using an Eastern pondhawk (Erythimus simplicicollis) dragonfly for demonstration, we quantify and visualize the wing twist and camber in both the chord-wise and span-wise directions, and discuss the implications of the results. In particular, a detailed analysis of the subtle deformation in the dragonflys right hindwing suggests that the muscles near the wing root could be used to induce chord-wise camber in the portion of the wing nearest the specimens body. We conclude by proposing a novel technique for modeling wing corrugation in the reconstructed flapping wings. In this method, displacement mapping is used to combine wing surface details measured from static wings with the reconstructed flapping wings, while not requiring any additional information be tracked in the high speed camera output.

Effects of Ipsilateral Wing-Wing Interactions on Aerodynamic Performance of Flapping Wings

Dragonflies are masters of using the ipsilateral wing-wing interaction for different kinds of flying modes. It has been discovered that the phase difference between ipsilateral forewings and hindwings plays important role on wing aerodynamic performance. In the current study, we continue our research of a modeled dragonfly in slow flight (Liang and Dong (2009)) by varying the phase difference between the forewings and hindwings and look at the changes of aerodynamic performance of hindwings. Results of this work will help with the design of quadwinged MAVs. NOMENCLATURE Ψf flapping or azimuth angle of forewing, deg Ψh flapping or azimuth angle of hindwing, deg ω angular rate of flapping motion, rad/s △δ phase difference of azimuth angle between forewing and hindwing, deg

An Integrated Analysis of a Dragonfly in Free Flight

There were few literatures on the discussion of the wing flexion and associated aerodynamic performance of dragonfly wings in dragonfly free flights, which are potential candidates for developing bio-inspired micro aerial vehicles (MAVs) that can match the hovering and maneuvering performance of winged insects. To this end, we experimentally measure the wing flexion of a free flying dragonfly during take-off using high-speed photogrammetry and three-dimensional surface reconstructions. From the collected data, analysis of body motion Euler angles, SVD analysis of wing kinematics, wing surface deformation and topologies, and direct numerical simulations will provide insights into the selection of flapping wing and kinematics for quad-winged MAV designs and applications.

Optimal Settings of Aerodynamic Performance Parameters in Hovering Flight

Flapping foils are being considered for lift generation and/or propulsion in design of Micro-Air Vehicles (MAVs). In this paper, a computational analysis of the aerodynamic performance of a 2D rigid flapping wing is conducted for examining the effect of basic morphological and kinematics parameters on unsteady flow field properties, wing loading, and lift efficiency. It focuses primarily on steady hovering flight with different kinds of wing trajectories. Key aerodynamic performance parameters are selected and evaluated to reflect three potential design modes of MAV flight, performance (or high-lift) mode, cruise (or high-efficiency) mode, and a “quiet” mode which reflects the overall steadiness of a particular set of wing kinematics. A fractional factorial design method is used to conduct the sensitivity study of performance parameters. Results aim to provide insight into the selection of wing planform and flapping kinematics for MAV designs.

Computational Study of Wing-Wake Interactions between Ipsilateral Wings of Dragonfly in Flight

Bilateral and ipsilateral wing-wing interactions can be commonly observed in insect flights. As a representative example of ipsilateral wing-wing interaction, dragonflies in flight have been widely studied. It has been discovered that they utilize changes of phase between ipsilateral forewings and hindwings at different kinds of flying mode. In the current study, we present a direct numerical simulation of a modeled dragonfly in slow flight as reported in Azuma et al (1985). Realistic morphologies of wing, body, and kinematics are used for maximum including wing and body features of a dragonfly. This work aims to study the relations between waketopology and aerodynamic performance due to wing-wing and wing-wake interactions of dragonfly ipsilateral wings. Current high fidelity numerical results are also compared with lowerfidelity aerodynamic modeling method discussed in Azuma et al (1985).

Computational Analysis of Hovering Hummingbird Flight

Different from large-size birds, hummingbirds are found to share more common flight patterns with insects, especially in hovering motion. Comparing to hovering insects, hummingbird wing kinematics uses apparent asymmetric motions during downstroke and upstroke. In current study, we present a direct numerical simulation of modeled hummingbird wings undergoing hover flight (Tobalske et al. JEB 2007). 3D wake structures and associated aerodynamic performance are of particular interests in this paper. Computational results are also compared with PIV experiments (Warrick et al. 2005 ).

On the symmetry of proper orthogonal decomposition modes of a low-aspect-ratio plate

In this paper, the symmetry property and corresponding virtual force contribution of the proper orthogonal decomposition (POD) modes are numerically investigated for the low-Reynolds number flows passing over a low-aspect-ratio pitching-plunging plate. It is found that the flow and its POD modes have the same reflectional symmetry about the spanwise central plane. However, about the crossflow central plane, the spatio-temporal flow symmetry results in a change of symmetry pattern every two POD modes, which corresponds to odd or even multiples of the vortex shedding frequency. Based on a wake survey method for virtual forces, the POD modes are further classified into two groups, thrust- and lift-producing modes, respectively. Results have also shown that the distinct symmetry properties of these modes can be used to identify the correlation between the wake structure and the hydrodynamic force production.

The Wing Kinematics Effects on Performance and Wake Structure Produced by Finite-Span Hovering Wings

Throughout the past decades, the mechanisms of aerodynamic force production and lift augmentation in flapping insect wings have been the subject of many thorough computational, experimental, and analytical investigations. Despite the fact that in nature, insect wings tend to be of low or moderate aspect ratio, most experimental and numerical studies in this area have focused on examining large- or infinite-aspect-ratio flapping foils. Systematic efforts are still being expected for detailed investigations of finite aspect ratio flapping foil undergoing hovering motion due to the difficulties in both experimental and numerical methodologies. In the current study, a DNS solver for computing flows with moving immersed boundaries has been used to explore the wake structures and aerodynamic performance of finite aspect-ratio flapping foils undergoing two different hovering motions: optimal fruit fly motion and optimal bumblebee motion. The results of these numerical simulations indicate that the wake topologies of these relatively low aspect-ratio foils are significantly different from that observed for infinite-/largeaspect-ratio foils and vary with the kinematics. Lift augmentation has been studied for “clap-andfling” wing-wing interaction and associated wake structures are investigated, too.

Vortex Formation of Freely Falling Plates

The problem of a freely uttering or tumbling plate is studied using direct numerical simulation (DNS) by solving the Navier-Stokes equations and body dynamic equations simultaneously. The vortex formation in the transient process and periodic motion of the falling plate is investigated. The correlation between the body kinematics and force generation is discussed. The dierent roles played by viscous force in uttering and tumbling plates are also pointed out.

Unsteady Flow and Its Reduced-Order Modeling of A Finite-Aspect-Ratio Flapping Foil

Direct numerical simulation (DNS) and proper orthogonal decomposition(POD)Galerkin projection are conducted for a 3-D foil undergoing pitching and plunging motion. POD analysis shows that most turbulent kinetic energy (96%) is contained by the first six POD modes, whereas the first four modes are sufficient to reconstruct the vortices formation in the far wake zone. Reconstruction coefficients of the first two POD modes could be accurately predicted by using a pressure correction based Galerkin projection method. Complex topological structures are found existing in iso-surfaces of velocity and Q-criterion of POD modes.