scholarly journals Petiolate wings: effects on the leading-edge vortex in flapping flight

2017 ◽  
Vol 7 (1) ◽  
pp. 20160084 ◽  
Author(s):  
Nathan Phillips ◽  
Kevin Knowles ◽  
Richard J. Bomphrey
Keyword(s):  
Lift Coefficient ◽  
Leading Edge ◽  
Field Measurements ◽  
Wing Surface ◽  
Tip Vortex ◽  
Leading Edge Vortex ◽  
Crane Flies ◽  
Image Velocimetry ◽  
Edge Vortex ◽  
Wing Stroke

The wings of many insect species including crane flies and damselflies are petiolate (on stalks), with the wing planform beginning some distance away from the wing hinge, rather than at the hinge. The aerodynamic impact of flapping petiolate wings is relatively unknown, particularly on the formation of the lift-augmenting leading-edge vortex (LEV): a key flow structure exploited by many insects, birds and bats to enhance their lift coefficient. We investigated the aerodynamic implications of petiolation P using particle image velocimetry flow field measurements on an array of rectangular wings of aspect ratio 3 and petiolation values of P = 1–3. The wings were driven using a mechanical device, the ‘Flapperatus’, to produce highly repeatable insect-like kinematics. The wings maintained a constant Reynolds number of 1400 and dimensionless stroke amplitude Λ * (number of chords traversed by the wingtip) of 6.5 across all test cases. Our results showed that for more petiolate wings the LEV is generally larger, stronger in circulation, and covers a greater area of the wing surface, particularly at the mid-span and inboard locations early in the wing stroke cycle. In each case, the LEV was initially arch-like in form with its outboard end terminating in a focus-sink on the wing surface, before transitioning to become continuous with the tip vortex thereafter. In the second half of the wing stroke, more petiolate wings exhibit a more detached LEV, with detachment initiating at approximately 70% and 50% span for P = 1 and 3, respectively. As a consequence, lift coefficients based on the LEV are higher in the first half of the wing stroke for petiolate wings, but more comparable in the second half. Time-averaged LEV lift coefficients show a general rise with petiolation over the range tested.

Scaling law for the lift force of autorotating falling seeds at terminal velocity

2017 ◽  
Vol 835 ◽  
pp. 406-420 ◽  
Author(s):  
Injae Lee ◽  
Haecheon Choi
Keyword(s):  
Numerical Simulation ◽  
Lift Force ◽  
Lift Coefficient ◽  
Scaling Law ◽  
Leading Edge ◽  
Terminal Velocity ◽  
Leading Edge Vortex ◽  
Actuator Disk ◽  
Vortex Theory ◽  
Edge Vortex

We provide a scaling law for the lift force of autorotating falling seeds at terminal velocity to describe the relation among the lift force, seed geometry and terminal descending and rotating velocities. Two theories, steady wing-vortex theory and actuator-disk theory, are examined to derive the scaling law. In the steady wing-vortex theory, the strength of a leading-edge vortex is scaled with the circulation around a wing and the lift force is modelled by the time derivative of vortical impulse, whereas the conservations of mass, linear and angular momentum, and kinetic energy across the autorotating falling seed are applied in the actuator-disk theory. To examine the validity of the theoretical results, an unsteady three-dimensional numerical simulation is conducted for flow around an autorotating seed (Acer palmatum) during free fall. The sectional lift coefficient predicted from the steady wing-vortex theory reasonably agrees with that from the numerical simulation, whereas the actuator-disk theory fails to provide an estimation of the sectional lift coefficient. The weights of 11 different species of autorotating falling seeds fall on the scaling law derived from the steady wing-vortex theory, suggesting that even a simple theoretical approach can explain how falling seeds support their weights by autorotation once the circulation from a leading-edge vortex is properly included in the theory.

scholarly journals Genetic Algorithm Based Optimization of Wing Rotation in Hover

Fluids ◽  
2018 ◽  
Vol 3 (3) ◽  
pp. 59 ◽  
Author(s):  
Alexander Gehrke ◽  
Guillaume Guyon-Crozier ◽  
Karen Mulleners
Keyword(s):  
Genetic Algorithm ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Airfoil Surface ◽  
Pitching Motion ◽  
Leading Edge Vortex ◽  
Final Population ◽  
Edge Vortex ◽  
Effective Angle

The pitching kinematics of an experimental hovering flapping wing setup are optimized by means of a genetic algorithm. The pitching kinematics of the setup are parameterized with seven degrees of freedom to allow for complex non-linear and non-harmonic pitching motions. Two optimization objectives are considered. The first objective is maximum stroke average efficiency, and the second objective is maximum stroke average lift. The solutions for both optimization scenarios converge within less than 30 generations based on the evaluation of their fitness. The pitching kinematics of the best individual of the initial and final population closely resemble each other for both optimization scenarios, but the optimal kinematics differ substantially between the two scenarios. The most efficient pitching motion is smoother and closer to a sinusoidal pitching motion, whereas the highest lift-generating pitching motion has sharper edges and is closer to a trapezoidal motion. In both solutions, the rotation or pitching motion is advanced with respect to the sinusoidal stroke motion. Velocity field measurements at selected phases during the flapping motions highlight why the obtained solutions are optimal for the two different optimization objectives. The most efficient pitching motion is characterized by a nearly constant and relatively low effective angle of attack at the start of the half stroke, which supports the formation of a leading edge vortex close to the airfoil surface, which remains bound for most of the half stroke. The highest lift-generating pitching motion has a larger effective angle of attack, which leads to the generation of a stronger leading edge vortex and higher lift coefficient than in the efficiency optimized scenario.

scholarly journals Numerical Investigation of a Dynamic Stall on a Single Rotating Blade

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 90
Author(s):  
Yin Ruan ◽  
Manfred Hajek
Keyword(s):  
Numerical Investigation ◽  
Vortex Structure ◽  
Leading Edge ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Dynamic Stall ◽  
Leading Edge Vortex ◽  
Pitching Airfoil ◽  
Edge Vortex ◽  
High Reynolds

Dynamic stall is a phenomenon on the retreating blade of a helicopter which can lead to excessive control loads. In order to understand dynamic stall and fill the gap between the investigations on pitching wings and full helicopter rotor blades, a numerical investigation of a single rotating and pitching blade is carried out. The flow phenomena thereupon including the Ω-shaped dynamic stall vortex, the interaction of the leading edge vortex with the tip vortex, and a newly noticed vortex structure originating inboard are examined; they show similarities to pitching wings, while also possessing their unique features of a rotating system. The leading edge/tip vortex interaction dominates the post-stall stage. A newly noticed swell structure is observed to have a great impact on the load in the post-stall stage. With such a high Reynolds number, the Coriolis force exerted on the leading edge vortex is negligible compared to the pressure force. The force history/vortex structure of the slice r/R = 0.898 is compared with a 2D pitching airfoil with the same harmonic pitch motion, and the current simulation shows the important role played by the swell structure in the recovery stage.

A Study of the Leading Edge Vortex and Tip Vortex on Prop-Fan Blades

1987 ◽  
Vol 109 (3) ◽  
pp. 325-331 ◽  
Author(s):  
C. M. Vaczy ◽  
D. C. McCormick
Keyword(s):  
Flow Visualization ◽  
Systematic Study ◽  
Leading Edge ◽  
Lower Surface ◽  
Tip Vortex ◽  
Leading Edge Vortex ◽  
Edge Loading ◽  
Oil Flow ◽  
Oil Flow Visualization ◽  
Edge Vortex

An oil flow visualization study was conducted on the blades of a counterrotating prop-fan model, the CRP-X1. A kink in the oil streaks was interpreted as an indication of the leading edge vortex reattachment line. The leading edge vortex was found to be on the lower surface for cases with negative leading edge loading and on the upper surface for cases with positive leading edge loading. For most cases, the leading edge vortex merged with a tip vortex. The results presented here represent the first systematic study of this phenomenon.

scholarly journals The three–dimensional leading–edge vortex of a ‘hovering’ model hawkmoth

1997 ◽  
Vol 352 (1351) ◽  
pp. 329-340 ◽  
Author(s):  
Coen van den Berg ◽  
Charles P. Ellington
Keyword(s):  
Wing Length ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Tip Vortex ◽  
Flow Visualisation ◽  
High Lift ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Wing Chord

Recent flow visualisation experiments with the hawkmoth, Manduca sexta , revealed small but clear leading–edge vortex and a pronounced three–dimensional flow. Details of this flow pattern were studied with a scaled–up, robotic insect (‘the flapper’) that accurately mimicked the wing movements of a hovering hawkmoth. Smoke released from the leading edge of the flapper wing confirmed the existence of a small, strong and stable leading–edge vortex, increasing in size from wingbase to wingtip. Between 25 and 75 % of the wing length, its diameter increased approximately from 10 to 50 % of the wing chord. The leading–edge vortex had a strong axial flow veolocity, which stabilized it and reduced its diamater. The vortex separated from the wing at approximately 75 % of the wing length and thus fed vorticity into a large, tangled tip vortex. If the circulation of the leading–edge vortex were fully used for lift generation, it could support up to two–thirds of the hawkmoth's weight during the downstroke. The growth of this circulation with time and spanwise position clearly identify dynamic stall as the unsteady aerodynamic mechanism responsible for high lift production by hovering hawkmoths and possibly also by many other insect species.

scholarly journals The Leading-Edge Vortex of Swift Wings

2017 ◽  
Author(s):  
Rowan Eveline Muir ◽  
Ignazio Maria Viola
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Wing Model ◽  
Image Velocimetry ◽  
Edge Vortex ◽  
First Time ◽  
Swept Wings ◽  
Sharp Leading Edge

1AbstractRecent investigations on the aerodynamics of natural fliers have illuminated the significance of the Leading-Edge Vortex (LEV) for lift generation in a variety of flight conditions. A well documented example of an LEV is that generated by aircraft with highly swept, delta shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowledge will serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, the wing of a common swift Apus apus is simplified to a model with swept wings and a sharp leading-edge, making it readily comparable to a model delta shaped wing of the same leading-edge geometry. Particle image velocimetry provides an understanding of the effect of the tapering swift wing on LEV development and stability, compared with the delta wing model. For the first time a dual LEV is recorded on a swift shaped wing, where it is found across all tested conditions. It is shown that the span-wise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the common swift is able to generate a dual LEV while gliding, potentially delaying vortex breakdown by exploiting other features non explored here, such as wing twist and flexibility. It is further suggested that the vortex system could be used to damp loading fluctuations, reducing energy expenditure, rather than for lift augmentation.

scholarly journals The leading-edge vortex of swift wing-shaped delta wings

2017 ◽  
Vol 4 (8) ◽  
pp. 170077 ◽  
Author(s):  
Rowan Eveline Muir ◽  
Abel Arredondo-Galeana ◽  
Ignazio Maria Viola
Keyword(s):  
Reynolds Number ◽  
Delta Wing ◽  
Leading Edge ◽  
Trailing Edge ◽  
Delta Wings ◽  
Leading Edge Vortex ◽  
Wing Model ◽  
Image Velocimetry ◽  
Edge Vortex ◽  
First Time

Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the leading-edge vortex (LEV) for lift generation in a variety of flight conditions. A well-documented example of an LEV is that generated by aircraft with highly swept, delta-shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowledge can serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, a model non-slender delta-shaped wing with a sharp leading edge is tested at low Reynolds number, along with a delta wing of the same design, but with a modified trailing edge inspired by the wing of a common swift Apus apus . The effect of the tapering swift wing on LEV development and stability is compared with the flow structure over the unmodified delta wing model through particle image velocimetry. For the first time, a leading-edge vortex system consisting of a dual or triple LEV is recorded on a swift wing-shaped delta wing, where such a system is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the trailing-edge geometry of the swift wing alone does not prevent the common swift from generating an LEV system comparable with that of a delta-shaped wing.

Aspect-ratio effects on rotating wings: circulation and forces

2015 ◽  
Vol 767 ◽  
pp. 497-525 ◽  
Author(s):  
Zakery R. Carr ◽  
Adam C. DeVoria ◽  
Matthew J. Ringuette
Keyword(s):  
Aspect Ratio ◽  
Lift Force ◽  
Slow Growth ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Tip Vortex ◽  
Trailing Edge ◽  
Data Set ◽  
Edge Vortex ◽  
Total Circulation

AbstractWe employ experiments to study aspect ratio ($\def\AR{A\mkern-8muR}\AR$) effects on the vortex structure, circulation and lift force for flat-plate wings rotating from rest at 45° angle of attack, which represents a simplified hovering-wing half-stroke. We use the time-varying, volumetric $\AR =2$ data of Carr et al. (Exp. Fluids, vol. 54, 2013, pp. 1–26), reconstructed from phase-locked, phase-averaged stereoscopic digital particle image velocimetry (S-DPIV), and an $\AR =4$ volumetric data set matching the span-based Reynolds number ($\mathit{Re}$) of $\AR =2$. For $\AR =1{-}4$ and $\mathit{Re}_{\mathit{span}}$ of $O$($10^{3}$–$10^{4}$), we directly measure the lift force. The total leading-edge-region circulation for $\AR =2$ and 4 compares best overall using a span-based normalization and for matching rotation angles. The total circulation increases across the span to the tip region, and is larger for $\AR =2$. After the startup, the total circulation for each $\AR$ has a similar slope and a slow growth. The first leading-edge vortex (LEV) and the tip vortex (TV) for $\AR =4$ move past the trailing edge, followed by substantial breakdown. For $\AR =2$ the outboard, aft-tilted LEV merges with the TV and resides over the tip, although breakdown also occurs. Where the LEV is ‘stable’ inboard, its circulation saturates for $\AR =2$ and the growth slows for $\AR =4$. Aft LEV tilting reduces the spanwise LEV circulation for each $\AR$. Both positive and negative axial flow are found in the first LEV for $\AR =2$ and 4, with the positive component being somewhat larger. This yields a generally positive (outboard) average vorticity flux. The average lift coefficient is essentially constant with $\AR$ from 1 to 4 during the slow growth phase, although the large-time behaviour shows a slight decrease in lift coefficient with increasing $\AR$. The S-DPIV data are used to obtain the lift impulse and the spanwise and streamwise components contributing to the lift coefficient. The spanwise contribution is similar for $\AR =2$ and 4, due to similar trailing-edge vortex interactions, LEV saturation behaviour and total circulation slopes. However, for $\AR =2$ the streamwise contribution is much larger, because of the stronger, coherent TV and aft-tilted LEV, which will create a relatively lower-pressure region over the tip.

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