scholarly journals A contralateral wing stabilizes a hovering hawkmoth under a lateral gust

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Aerodynamic Force ◽  
Leading Edge ◽  
Static Stability ◽  
The Body ◽  
Leeward Side ◽  
Water Tank ◽  
Roll Moment ◽  
Close Proximity ◽  
Edge Vortex ◽  
Hinge Points

AbstractPrevious analysis on the lateral stability of hovering insects, which reported a destabilizing roll moment due to a lateral gust, has relied on the results of a single wing without considering a presence of the contralateral wing (wing-wing interaction). Here, we investigated the presence of the contralateral wing on the aerodynamic and flight dynamic characteristics of a hovering hawkmoth under a lateral gust. By employing a dynamically scaled-up mechanical model and a servo-driven towing system installed in a water tank, we found that the presence of the contralateral wing plays a significant role in the lateral static stability. The contralateral wing mitigated an excessive aerodynamic force on the wing at the leeward side, thereby providing a negative roll moment to the body. Digital particle image velocimetry revealed an attenuated vortical system of the leading-edge vortex. An excessive effective angle of attack in the single wing case, which was caused by the root vortex of previous half stroke, was reduced by a downwash of the contralateral wing. The contralateral wing also relocated a neutral point in close proximity to the wing hinge points above the actual center of gravity, providing a practical static margin to a hovering hawkmoth.

Aerodynamic characteristics of flapping wings under steady lateral inflow

2019 ◽  
Vol 870 ◽  
pp. 735-759 ◽  
Author(s):  
Jong-Seob Han ◽  
Anh Tuan Nguyen ◽  
Jae-Hung Han
Keyword(s):  
Aerodynamic Force ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Lateral Direction ◽  
Roll Moment ◽  
Centre Of Gravity ◽  
Lateral Inflow ◽  
Force Moment ◽  
Edge Vortex ◽  
Wing Interaction

This experimental study investigates the effect of a uniform lateral inflow on the aerodynamic characteristics of flapping wings. Seven designated sideward ratios in the hovering condition and in the presence of a contralateral wing and a body were taken into account as variables in order to secure a better understanding of wing–wing and/or wing–body interactions under the lateral inflow. Our results from the single-wing cases clarified that an inflow running from the wingroot strengthened the leading-edge vortex, thereby augmenting the aerodynamic force/moment. The inflow running in the opposite direction drastically bent the leading-edge vortex to the trailing edge, but the cycle-averaged aerodynamic force/moment was barely changed. This led to substantial imbalances in the force/moment on the two wings. The roll moment on a centre of gravity and the static margin suggested flight instability in the lateral direction, similar to previous studies. We found that the wing–wing interaction was not completely negligible overall under a lateral inflow. A massive downwash induced by the wing on the windward side nearly neutralized the aerodynamic force/moment augmentations on the other wing with lower effective angles of attack. The wing–wing interaction also gave rise to a low-lift high-drag situation during the pitching-up wing rotation, resulting in greater side force derivatives than the theory of flapping counterforce. Further calculations of the roll moment and the static margin with the centre of gravity showed that the wing–wing interaction can improve static stability in the lateral direction. This mainly stemmed from both the attenuation of the lift augmentation and the elimination of the positive roll moment of the flapping-wing system.

scholarly journals Schlieren photography on freely flying hawkmoth

2018 ◽  
Vol 14 (5) ◽  
pp. 20180198 ◽  
Author(s):  
Yun Liu ◽  
Jesse Roll ◽  
Stephen Van Kooten ◽  
Xinyan Deng
Keyword(s):  
Aerodynamic Force ◽  
Leading Edge ◽  
Vortical Flow ◽  
Natural Setting ◽  
Optical Flow Method ◽  
Flying Insects ◽  
Flow Features ◽  
Potential Applications ◽  
Edge Vortex ◽  
Schlieren Photography

The aerodynamic force on flying insects results from the vortical flow structures that vary both spatially and temporally throughout flight. Due to these complexities and the inherent difficulties in studying flying insects in a natural setting, a complete picture of the vortical flow has been difficult to obtain experimentally. In this paper, Schlieren , a widely used technique for highspeed flow visualization, was adapted to capture the vortex structures around freely flying hawkmoth ( Manduca ). Flow features such as leading-edge vortex, trailing-edge vortex, as well as the full vortex system in the wake were visualized directly. Quantification of the flow from the Schlieren images was then obtained by applying a physics-based optical flow method, extending the potential applications of the method to further studies of flying insects.

Wake Behavior Around Flapping Wings of Model Hawkmoth Moving Sideways

2019 ◽  
Author(s):  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Particle Image ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Digital Particle Image Velocimetry ◽  
Flapping Wings ◽  
Windward Side ◽  
Leeward Side ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
Edge Vortex

Abstract This study investigated nearwake behaviors around flapping wings moving sideways. A dynamically scaled-up flapping manipulator was installed on a servo-driven towing carriage to give the sideways movement. In the single wing configuration, the wing in the windward side did not encounter any noticeable effects on the aerodynamic characteristics. The wing in the leeward side, on the other hand, experienced a substantial lift augmentation. We found a stretched leading-edge vortex (LEV) on the wing in the leeward side, implying the additional feeding flux into the LEV. In this case, the moving sideways gave a continuous lateral wind, which became the source to maintain the lift augmentation with the less downward component. We also found that the moving sideways rather intensified the interaction between the wake of the wing in the windward side and the contralateral wing, i.e., the wing-wake interaction. Accordingly, the lift augmentation on the wing in the leeward side practically disappeared by the wing-wake interaction. A digital particle image velocimetry for nearwake behaviors found the less developed trailing-edge shear layer and wingroot vortex traces. This implied that the massive downwash induced by the wing in the windward side was the main source to neutralize the lift augmentation on the contralateral wing.

scholarly journals Aerodynamic Performance of a Passive Pitching Model on Bionic Flapping Wing Micro Air Vehicles

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Jinjing Hao ◽  
Jianghao Wu ◽  
Yanlai Zhang
Keyword(s):  
High Efficiency ◽  
Aerodynamic Force ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Torsional Stiffness ◽  
Important Goal ◽  
Edge Vortex ◽  
Yaw Moment ◽  
Air Vehicles

Reducing weight and increasing lift have been an important goal of using flapping wing micro air vehicles (FWMAVs). However, FWMAVs with mechanisms to limit the angle of attack (α) artificially by active force cannot meet specific requirements. This study applies a bioinspired model that passively imitates insects’ pitching wings to resolve this problem. In this bionic passive pitching model, the wing root is equivalent to a torsional spring. α obtained by solving the coupled dynamic equation is similar to that of insects and exhibits a unique characteristic with two oscillated peaks during the middle of the upstroke/downstroke under the interaction of aerodynamic, torsional, and inertial moments. Excess rigidity or flexibility deteriorates the aerodynamic force and efficiency of the passive pitching wing. With appropriate torsional stiffness, passive pitching can maintain a high efficiency while enhancing the average lift by 10% than active pitching. This observation corresponds to a clear enhancement in instantaneous force and a more concentrated leading edge vortex. This phenomenon can be attributed to a vorticity moment whose component in the lift direction grows at a rapid speed. A novel bionic control strategy of this model is also proposed. Similar to the rest angle in insects, the rest angle of the model is adjusted to generate a yaw moment around the wing root without losing lift, which can assist to change the attitude and trajectory of a FWMAV during flight. These findings may guide us to deal with various conditions and requirements of FWMAV designs and applications.

Vortex force of an impulsively started plate at high angle of attack

2017 ◽  
Vol 27 (11) ◽  
pp. 2402-2414
Author(s):  
Xiang Fu ◽  
Gaohua Li ◽  
Fuxin Wang
Keyword(s):  
Aerodynamic Force ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Aerodynamic Forces ◽  
Total Drag ◽  
Content Type ◽  
Vortical Structures ◽  
Edge Vortex ◽  
The Individual ◽  
Practical Implications

Purpose A quantitative study that can identify the primary aerodynamic forces and relate them to individual vortical structures is lacking. The paper aims to clarify the quantitative relationships between the aerodynamic forces and vortical structures. Design/methodology/approach The various contributions to the aerodynamic forces on the two-dimensional impulsively started plate are investigated from the perspective of the vorticity moment theorem. The angles of attacks are set to 45°, 58.5° and 72°, while the Reynolds number is 10,000 based on the chord length. Compared with the traditional pressure force analysis, this theorem not only tells us the total aerodynamic force during the motion, but also enables us to quantify the forces contributed from the fluid elements with non-zero vorticity. Findings It is found that the time-dependent force behaviors are dominated by the formations and evolutions of these vortical structures. The analysis of the time-averaged forces demonstrates that the lift contributed from the leading edge vortex (LEV) is nearly four times larger than the total lift and the drag contributed from the starting vortex (SV) is almost equal to the total drag when the angle of attack (AoA) increases to 72°, which means the LEV is “lift structure” whereas the SV is “drag structure”. Practical implications The present method provides a better perspective for flow control and drag reduction by relating the forces directly to the individual vorticity structures. Originality/value In this paper, the Vorticity Moment Theory is first used to study the quantitative relationships between the aerodynamic forces and the vortices.

scholarly journals Evolution of the leading-edge vortex over a flapping wing mechanism

2020 ◽  
Vol 14 (2) ◽  
pp. 6888-6894
Author(s):  
Muhamad Ridzuan Arifin ◽  
A.F.M. Yamin ◽  
A.S. Abdullah ◽  
M.F. Zakaryia ◽  
S. Shuib ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Flapping Wing ◽  
Unsteady State ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Advance Ratio ◽  
Lift Enhancement ◽  
Lift And Drag

Leading-edge vortex governs the aerodynamic force production of flapping wing flyers. The primary factor for lift enhancement is the leading-edge vortex (LEV) that allows for stall delay that is associated with unsteady fluid flow and thus generating extra lift during flapping flight. To access the effects of LEV to the aerodynamic performance of flapping wing, the three-dimensional numerical analysis of flow solver (FLUENT) are fully applied to simulate the flow pattern. The time-averaged aerodynamic performance (i.e., lift and drag) based on the effect of the advance ratio to the unsteadiness of the flapping wing will result in the flow regime of the flapping wing to be divided into two-state, unsteady state (J<1) and quasi-steady-state(J>1). To access the benefits of aerodynamic to the flapping wing, both set of parameters of velocities 2m/s to 8m/s at a high flapping frequency of 3 to 9 Hz corresponding to three angles of attacks of α = 0o to α = 30o. The result shows that as the advance ratio increases the generated lift and generated decreases until advance ratio, J =3 then the generated lift and drag does not change with increasing advance ratio. It is also found that the change of lift and drag with changing angle of attack changes with increasing advance ratio. At low advance ratio, the lift increase by 61% and the drag increase by 98% between α =100 and α =200. The lift increase by 28% and drag increase by 68% between α = 200 and α = 300. However, at high advance ratio, the lift increase by 59% and the drag increase by 80% between α =100 and α = 200, while between α =200 and α =300 the lift increase by 20% and drag increase by 64%. This suggest that the lift and drag slope decreases with increasing advance ratio. In this research, the results had shown that in the unsteady state flow, the LEV formation can be indicated during both strokes. The LEV is the main factor to the lift enhancement where it generated the lower suction of negative pressure. For unsteady state, the LEV was formed on the upper surface that increases the lift enhancement during downstroke while LEV was formed on the lower surface of the wing that generated the negative lift enhancement. The LEV seem to breakdown at the as the wing flap toward the ends on both strokes.      

Structure of Diffuser Stall and Unsteady Vortices in a Centrifugal Compressor With Vaned Diffuser

2016 ◽  
Author(s):  
Nobumichi Fujisawa ◽  
Sota Ikezu ◽  
Yutaka Ohta
Keyword(s):  
Centrifugal Compressor ◽  
Leading Edge ◽  
Rotating Stall ◽  
Design Flow ◽  
Tip Leakage Flow ◽  
Vaned Diffuser ◽  
Tip Leakage ◽  
Close Proximity ◽  
Edge Vortex ◽  
Flow Blockage

The characteristics of a diffuser rotating stall and the evolution of a vortex generated on the diffuser leading edge (i.e., leading-edge vortex (LEV)) in a centrifugal compressor were investigated using experiments and numerical analyses. The experimental results showed that both impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. Both the stall cells existed only on the shroud side of the flow passages, which is in close proximity to the source location of the LEV. The numerical results showed that the LEV is a combination of a separated vortex near the leading edge and the extended tip-leakage flow from the impeller. In the partial flow operation, the LEV develops as the velocity decreases in the diffuser passages and forms a huge flow blockage within the diffuser passages. Therefore, the LEV may be considered to be one of the causes of diffuser stall in the centrifugal compressor.

scholarly journals Flying in reverse: kinematics and aerodynamics of a dragonfly in backward free flight

2018 ◽  
Vol 15 (143) ◽  
pp. 20180102 ◽  
Author(s):  
Ayodeji T. Bode-Oke ◽  
Samane Zeyghami ◽  
Haibo Dong
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Force Production ◽  
Leading Edge ◽  
The Body ◽  
Body Posture ◽  
Immersed Boundary ◽  
Reconstruction Method ◽  
Free Flight ◽  
The Us

In this study, we investigated the backward free flight of a dragonfly, accelerating in a flight path inclined to the horizontal. The wing and body kinematics were reconstructed from the output of three high-speed cameras using a template-based subdivision surface reconstruction method, and numerical simulations using an immersed boundary flow solver were conducted to compute the forces and visualize the flow features. During backward flight, the dragonfly maintained an upright body posture of approximately 90° relative to the horizon. The upright body posture was used to reorient the stroke plane and the flight force in the global frame; a mechanism known as ‘force vectoring’ which was previously observed in manoeuvres of other flying animals. In addition to force vectoring, we found that while flying backward, the dragonfly flaps its wings with larger angles of attack in the upstroke (US) when compared with forward flight. Also, the backward velocity of the body in the upright position enhances the wings' net velocity in the US. The combined effect of the angle of attack and wing net velocity yields large aerodynamic force generation in the US, with the average magnitude of the force reaching values as high as two to three times the body weight. Corresponding to these large forces was the presence of a strong leading edge vortex (LEV) at the onset of US which remained attached up until wing reversal. Finally, wing–wing interaction was found to enhance the aerodynamic performance of the hindwings (HW) during backward flight. Vorticity from the forewings’ trailing edge fed directly into the HW LEV to increase its circulation and enhance force production.

Effect of wing mass on the free flight of a butterfly-like model using immersed boundary–lattice Boltzmann simulations

2019 ◽  
Vol 877 ◽  
pp. 614-647 ◽  
Author(s):  
K. Suzuki ◽  
I. Okada ◽  
M. Yoshino
Keyword(s):  
Lattice Boltzmann ◽  
Total Mass ◽  
Aerodynamic Force ◽  
Inertial Force ◽  
Leading Edge ◽  
The Body ◽  
Immersed Boundary ◽  
Mass Ratio ◽  
Free Flight ◽  
Lattice Boltzmann Simulations

The wings of butterflies are relatively heavier than those of other insects, and the inertial force and torque due to the wing mass are likely to have a significant effect on agility and manoeuvrability in the flapping flight of butterflies. In the present study, the effect of wing mass on the free flight of butterflies is investigated by numerical simulations based on an immersed boundary–lattice Boltzmann method. We use a butterfly-like model consisting of two square wings with mass connected by a rod-shaped body. We simulate the free flights of the model by changing the ratio of the wing mass to the total mass of the model and also changing the mass distributions of the wings. As a result, we find that the aerodynamic vertical and horizontal forces decrease as the wing-mass ratio increases, since for a large wing-mass ratio the body has large vertical and horizontal oscillations in each stroke and consequently the speeds of the wing tip and the leading edge relatively decrease. In addition, we find that the wing-mass ratio has a dominant effect on the rotational motion of the model, and a large wing-mass ratio reduces aerodynamic force and intensifies the time variation of the pitching angle. From the results of our free flight simulations, we clarify the critical wing-mass ratio between upward flight and downward flight and find that the critical wing-mass ratio is a function of the non-dimensional total mass and almost independent of the wing length. Then, we evaluate the effect of the wing-mass distribution on the critical wing-mass ratio. Finally, we discuss the limitations of the model.

scholarly journals The vortex wake of a ‘hovering’ model hawkmoth

1997 ◽  
Vol 352 (1351) ◽  
pp. 317-328 ◽  
Author(s):  
Coen van den Berg ◽  
Charles P. Ellington
Keyword(s):  
Lift Force ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
The Body ◽  
Tip Vortex ◽  
Vortex Rings ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Visualization Experiments

Visualization experiments with Manduca sexta have revealed the presence of a leading–edge vortex and a highly three–dimensional flow pattern. To further investigate this important discovery, a scaled–up robotic insect was built (the ‘flapper’) which could mimic the complex movements of the wings of a hovering hawkmoth. Smoke released from the leading edge of the flapper wing revealed a small but strong leading–edge vortex on the downstroke. This vortex had a high axial flow velocity and was stable, separating from the wing at approximately 75 % of the wing length. It connected to a large, tangled tip vortex, extending back to a combining stopping and starting vortex from pronation. At the end of the downstroke, the wake could be approximated as one vortex ring per wing. Based on the size and velocity of the vortex rings, the mean lift force during the downstroke was estimated to be about 1.5 times the body weight of a hawkmoth, confirming that the downstroke is the main provider of lift force.

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