Influence of aspect ratio on wing–wake interaction for flapping wing in hover

Addo-Akoto, Reynolds; Han, Jong-Seob; Han, Jae‐Hung

doi:10.1007/s00348-019-2816-0

Cited by 12 publications

(11 citation statements)

References 46 publications

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Section: Sensitivity To Input Parametersmentioning

confidence: 99%

“…I believe it is useful to stop here and consider the aspect ratio effect on wake capture lift, in light of some of the recent findings within the flapping wing aerodynamics field [35,36]. In particular, a recent experimental campaign from Addo-Akoto et al [35] considered the wing aspect ratio influence on wake capture aerodynamics. The main outcome of this study was that lower aspect ratio values lead to a higher wake capture lift, which in turn can somehow compensate for the lower lift production of lower aspect ratio wings within the wing translation phase after wake capture has diminished.…”

Section: Sensitivity To Input Parametersmentioning

confidence: 99%

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A simple model of wake capture aerodynamics

Nabawy

2023

J. R. Soc. Interface.

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Flapping wings may encounter or ‘capture’ the wake from previous half-stroke, leading to local changes in the instantaneous aerodynamic force on the wing at the start of each half-stroke. In this paper, I developed a simple approach to integrating prediction of these wake capture effects into existing analytical quasi-steady models for hovering insect flapping flight. The local wake flow field is modelled as an additional induced velocity component normal to the stroke plane of the flapping motion that is blended/switched in at the start of each half-stroke. Comparison of model results against experimental data in the literature shows satisfactory agreement in predicting the wake capture lift and drag variations for eight different test cases. Sensitivity analysis shows that the form of the translation velocity time history has a significant effect on the magnitude of wake capture forces. Profiles that retain high translational velocity right up to stroke reversal evoke a much larger effect from wake capture compared with sinusoidal. This result is significant because while constant flapping translation velocity profiles can be generated in the laboratory, the very high accelerations required near stroke reversals incur high mechanical cost that prevents practical adoption in nature or engineered flapping flight vehicles.

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Section: Sensitivity To Input Parametersmentioning

confidence: 99%

Section: Sensitivity To Input Parametersmentioning

confidence: 99%

A simple model of wake capture aerodynamics

Nabawy

2023

J. R. Soc. Interface.

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“…They also noted that smaller acceleration and pitching durations lead to higher peaks in lift and drag coefficients at the beginning of a flapping half-stroke, suggesting stronger stroke reversal aerodynamic effects for those cases. Addo-Akoto et al [26] also used force measurements and DPIV to study wing-wake interaction of a 3D Drosophila wing model. They found a strong downward jet near the wing root induced by the residual TEV-starting vortex (SV) pair in the subsequent half-stroke.…”

Section: Introductionmentioning

confidence: 99%

Capturing wake capture: a 2D numerical investigation into wing–wake interaction aerodynamics

Nabawy

2022

Bioinspir. Biomim.

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A wing generating lift leaves behind a region of disturbed air in the form of a wake. For a hovering insect, the wings must return through the wake produced by the previous half-stroke and this can have significant effects on the aerodynamic performance. This paper numerically investigates 2D wings interacting with their own wake at Reynolds numbers of 102 and 103, enabling an improved understanding of the underlying physics of the ‘wake capture’ aerodynamic mechanism of insect flight. We adopt a simple kinematic motion pattern comprised of a translational stroke motion followed by a complete stop to expose wake interaction effects. Representative stroke distance to chord ratios between 1.5 and 6.0 are considered, enabling different leading-edge vortex attachment states. We also allow pitching rotation towards the end of stroke, leading to wake intercepting angles of 135º, 90º, and 45º, analogous to delayed, symmetric, and advanced pitching rotations of insect wings. It is shown that both vortex suction and jet flow impingement mechanisms can lead to either positive or negative effects depending on the leading-edge vortex attachment state, and that stroke distances resulting in a detached/attached leading-edge vortex lead to beneficial/detrimental wake interaction lift. Pitching rotation at the end of the stroke motion is found to induce a strong rotational trailing-edge vortex. For advanced pitching, this rotational trailing-edge vortex serves to enable either a stronger flow impingement effect leading to positive wake interaction lift if the leading-edge vortex is detached, or a less favourable vortex suction effect leading to negative wake interaction lift if the leading-edge vortex is closely attached. The higher Reynolds number led to faster development of the wake vortices, but the primary wake interaction mechanisms remained the same for both Reynolds numbers.

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“…The complex nature of insect wing design coupled with three-dimensional wing deformation (bend, torsion, and geometric twist) has led to the use of rigid wings in many studies. The rigid wings are rather made to mimic insect-like motions with a hawkmothlike [7][8][9], fruitfly-like [10][11][12][13][14] or a rectangular wing [15][16][17][18] planform. Studies employing rigid wings have unraveled essential aerodynamic mechanisms, such as delayed stall, rotational lift, and wake capture, which are now known to be important for lift augmentation of insect flight [7,10,13].…”

Section: Introductionmentioning

confidence: 99%

“…The rigid wings are rather made to mimic insect-like motions with a hawkmothlike [7][8][9], fruitfly-like [10][11][12][13][14] or a rectangular wing [15][16][17][18] planform. Studies employing rigid wings have unraveled essential aerodynamic mechanisms, such as delayed stall, rotational lift, and wake capture, which are now known to be important for lift augmentation of insect flight [7,10,13]. However, reports from other studies show that wing flexibility improves the aerodynamic performance in comparison to the rigid wing [8, 19-22, 55, 58, 59].…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic performance of flexible flapping wings deformed by slack angle

Addo-Akoto

Han

2020

Bioinspir. Biomim.

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Wing flexibility is unavoidable for flapping wing flyers to ensure a lightweight body and for higher payload allowances on board. It also effectively minimizes the inertia force from high-frequency wingbeat motion. However, related studies that attempt to clarify the essence of wing flexibility remain insufficient. Here, a parametric study of a flexible wing was conducted as part of the effort to build an aerodynamic model and analyze its aerodynamic performance. The quasi-steady modeling was adopted with experimentally determined translational forces. These forces were determined from 84 flexible wing cases while varying the angle of attack at the wing root α r and the flexibility parameter, slack angle θ S, with 19 additional rigid wing cases. This study found α r for optimum lift generation to exceed 45° irrespective of θ S. The coefficient curves were well-fitted with a cubed-sine function. The model was rigorously validated with various wing kinematics, giving a good estimation of the experimental results. The estimated error was less than 5%, 6%, and 8% for the lift, drag, and moment, respectively, considering fast to moderate wing kinematics. The study was extended to analyze the pure aerodynamic performance of the flexible wing. The most suitable wing for a flapping-wing micro-aerial vehicle wing design with a simple vein structure was found to be the 5° slack-angled wing. The inference from this study further shows that a small amount of deformation is needed to increase the lift, as observed in natural flyers. Thus, wing deformation could allow living flyers to undertake less pitching motion in order to reduce the mechanical power and increase the efficiency of their wings.

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Influence of aspect ratio on wing–wake interaction for flapping wing in hover

Cited by 12 publications

References 46 publications

A simple model of wake capture aerodynamics

A simple model of wake capture aerodynamics

Capturing wake capture: a 2D numerical investigation into wing–wake interaction aerodynamics

Aerodynamic performance of flexible flapping wings deformed by slack angle

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