Tuyen Quang Le

Improvement of the aerodynamic performance by wing flexibility and elytra--hind wing interaction of a beetle during forward flight.

In this work, the aerodynamic performance of beetle wing in free-forward flight was explored by a three-dimensional computational fluid dynamics (CFDs) simulation with measured wing kinematics. It is shown from the CFD results that twist and camber variation, which represent the wing flexibility, are most important when determining the aerodynamic performance. Twisting wing significantly increased the mean lift and camber variation enhanced the mean thrust while the required power was lower than the case when neither was considered. Thus, in a comparison of the power economy among rigid, twisting and flexible models, the flexible model showed the best performance. When the positive effect of wing interaction was added to that of wing flexibility, we found that the elytron created enough lift to support its weight, and the total lift (48.4 mN) generated from the simulation exceeded the gravity force of the beetle (47.5 mN) during forward flight.

Morphological effect of a scallop shell on a flapping-type tidal stream generator

Inspired by nature, flapping-type tidal stream generators have been introduced in recent years. The improvement in their power generation ability is known to be a critical factor in the success of these generators. So far, corrugation and camber observed in flying insects and swimming animals are known to enhance the performance of a flapping-type propulsive system. In this study, we explore the effect of corrugation and camber in a system that mimics a scallop shell in terms of its ability to extract flow energy through a two-dimensional Navier-Stokes simulation. The simulations show that the size and the activity of the leading edge vortex are strongly affected by the morphological factors of the mimicked foils, the effects of which are then advantageous in terms of the power efficiency of the flapping-type tidal stream generator. Eventually, an optimal mimicked foil, as suggested based on the morphological effects, would be a good alternative type of foil with a typical section with regard to the hydrodynamic performance and structural properties of tidal stream generators.

Numerical investigation of the aerodynamic characteristics of a hovering Coleopteran insect.

The aerodynamic characteristics of the Coleopteran beetle species Epilachna quadricollis, a species with flexible hind wings and stiff elytra (fore wings), are investigated in terms of hovering flight. The flapping wing kinematics of the Coleopteran insect are modeled through experimental observations with a digital high-speed camera and curve fitting from an ideal harmonic kinematics model. This model numerically simulates flight by estimating a cross section of the wing as a two-dimensional elliptical plane. There is currently no detailed study on the role of the elytron or how the elytron-hind wing interaction affects aerodynamic performance. In the case of hovering flight, the relatively small vertical or horizontal forces generated by the elytron suggest that the elytron makes no significant contribution to aerodynamic force.

Flexible Wing Kinematics of a Free-Flying Beetle (Rhinoceros Beetle Trypoxylus Dichotomus)

Detailed 3-Dimensional (3D) wing kinematics was experimentally presented in free flight of a beetle, Trypoxylus dichotomus, which has a pair of elytra (forewings) and flexible hind wings. The kinematic parameters such as the wing tip trajectory, angle of attack and camber deformation were obtained from a 3D reconstruction technique that involves the use of two synchronized high-speed cameras to digitize various points marked on the wings. Our data showed outstanding characteristics of deformation and flexibility of the beetle’s hind wing compared with other measured insects, especially in the chordwise and spanwise directions during flapping motion. The hind wing produced 16% maximum positive camber deformation during the downstroke. It also experienced twisted shape showing large variation of the angle of attack from the root to the tip during the upstroke.

Effect of Chord Flexure on Aerodynamic Performance of a Flapping Wing

Inspired by the fact that a high flexible wing in nature generates high aerodynamic performance, we investigated the aerodynamic performance of the flapping wing with different chord flexures. The unsteady, incompressible, and viscous flow over airfoil NACA0012 in a plunge motion was analyzed by using Navier-Stokes equation. Grid deformation, in which finite element and interpolation ideas are mixed, was introduced for computing large grid deformation caused by the chord flexures. We explored the optimal phase angle for thrust force and propulsive efficiency by varying the chord flexure from 0.05 to 0.7 when reduced frequency and plunge amplitude were fixed. Throughout parametric study on the phase angle and chord flexure amplitude, the maximum thrust force is achieved near at 0° in all given conditions, meanwhile, it is found that the optimal phase angle has dependency of chord flexure amplitude, which achieves higher aerodynamic performance compared to previous studies. These findings will provide a useful guideline for determining wing flexibility in design of a bio-mimetic air vehicle.

How Could Beetle's Elytra Support Their Own Weight during Forward Flight?

The aerodynamic role of the elytra during a beetle’s flapping motion is not well-elucidated, although it is well-recognized that the evolution of elytra has been a key in the success of coleopteran insects due to their protective function. An experimental study on wing kinematics reveals that for almost concurrent flapping with the hind wings, the flapping angle of the elytra is 5 times smaller than that of the hind wings. Then, we explore the aerodynamic forces on elytra in free forward flight with and without an effect of elytron-hind wing interaction by three-dimensional numerical simulation. The numerical results show that vertical force generated by the elytra without interaction is not sufficient to support even its own weight. However, the elytron-hind wing interaction improves the vertical force on the elytra up to 80%; thus, the total vertical force could fully support its own weight. The interaction slightly increases the vertical force on the hind wind by 6% as well.

Flow visualization of rhinoceros beetle ( Trypoxylus dichotomus ) in free flight

Aerodynamic characteristics of the beetle, Trypoxylus dichotomus, which has a pair of elytra (forewings) and flexible hind wings, are investigated. Visualization experiments were conducted for various flight conditions of a beetle, Trypoxylus dichotomus: free, tethered, hovering, forward and climbing flights. Leading edge, trailing edge and tip vortices on both wings were observed clearly. The leading edge vortex was stable and remained on the top surface of the elytron for a wide interval during the downstroke of free forward flight. Hence, the elytron may have a considerable role in lift force generation of the beetle. In addition, we reveal a suction phenomenon between the gaps of the hind wing and the elytron in upstroke that may improve the positive lift force on the hind wing. We also found the reverse clap-fling mechanism of the T. dichotomus beetle in hovering flight. The hind wings touch together at the beginning of the upstroke. The vortex generation, shedding and interaction give a better understanding of the detailed aerodynamic mechanism of beetle flight.

Non-Jumping Take off Performance in Beetle Flight (Rhinoceros Beetle Trypoxylus dichotomus)

In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes off without jumping. In this study, we used 3-Dimensional (3D) high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be considered as a main source of lift for heavy beetle.

Experimental and numerical study of a dual configuration for a flapping tidal current generator.

In this study, we conduct experimental and consecutive numerical analyses of a flapping tidal current generator with a mirror-type dual configuration with front-swing and rear-swing flappers. An experimental analysis of a small-scale prototype is conducted in a towing tank, and a numerical analysis is conducted by means of two-dimensional computational fluid dynamics simulations with an in-house code. An experimental study with a controller to determine the target arm angle shows that the resultant arm angle is dependent on the input arm angle, the frequency, and the applied load, while a high pitch is obtained simply with a high input arm angle. Through a parametric analysis conducted while varying these factors, a high applied load and a high input arm angle were found to be advantageous. Moreover, the optimal reduced frequency was found to be 0.125 in terms of the power extraction. In consecutive numerical investigations with the kinematics selected from the experiments, it was found that a rear-swing flapper contributes to the total amount of power more than a front-swing flapper with a distance of two times the chord length and with a 90° phase difference between the two. The high contribution stems from the high power generated by the rear-swing flapper, which mimics the tail fin movement of a dolphin along a flow, compared to a plunge system or a front-swing system, which mimics the tail fin movement of a dolphin against a flow. It is also due to the fact that the shed vorticities of the front-swing flapper slightly affect negatively or even positively the power performance of the rear-swing system at a given distance and phase angle.

Two- and Three-Dimensional Simulations of Beetle Hind Wing Flapping during Free Forward Flight

Aerodynamic characteristic of the beetle, Trypoxylus dichotomus, which has a pair of elytra (forewings) and hind wings, is numerically investigated. Based on the experimental results of wing kinematics, two-dimensional (2D) and three-dimensional (3D) computational fluid dynamic simulations were carried out to reveal aerodynamic performance of the hind wing. The roles of the spiral Leading Edge Vortex (LEV) and the spanwise flow were clarified by comparing 2D and 3D simulations. Mainly due to pitching down of chord line during downstroke in highly inclined stroke plane, relatively high averaged thrust was produced in the free forward flight of the beetle. The effects of the local corrugation and the camber variation were also investigated for the beetle’s hind wings. Our results show that the camber variation plays a significant role in improving both lift and thrust in the flapping. On the other hand, the local corrugation pattern has no significant effect on the aerodynamic force due to large angle of attack during flapping.