scholarly journals The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing

2015 ◽  
Vol 10 (5) ◽  
pp. 056020 ◽  
Author(s):  
Nathan Phillips ◽  
Kevin Knowles ◽  
Richard J Bomphrey
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Flapping Wing ◽  
Leading Edge Vortex ◽  
Edge Vortex

scholarly journals Leading-Edge Vortex Characteristics of Low-Aspect-Ratio Sweptback Plates at Low Reynolds Number

2021 ◽  
Vol 11 (6) ◽  
pp. 2450
Author(s):  
Jong-Seob Han ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Leading Edge ◽  
Flapping Wing ◽  
Flat Plates ◽  
Leading Edge Vortex ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Oil Flow ◽  
Edge Vortex

A sweptback angle can directly regulate a leading-edge vortex on various aerodynamic devices as well as on the wings of biological flyers, but the effect of a sweptback angle has not yet been sufficiently investigated. Here, we thoroughly investigated the effect of the sweptback angle on aerodynamic characteristics of low-aspect-ratio flat plates at a Reynolds number of 2.85 × 104. Direct force/moment measurements and surface oil-flow visualizations were conducted in the wind-tunnel B at the Technical University of Munich. It was found that while the maximum lift at an aspect ratio of 2.03 remains unchanged, two other aspect ratios of 3.13 and 4.50 show a gradual increment in the maximum lift with an increasing sweptback angle. The largest leading-edge vortex contribution was found at the aspect ratio of 3.13, resulting in a superior lift production at a sufficient sweptback angle. This is similar to that of a revolving/flapping wing, where an aspect ratio around three shows a superior lift production. In the oil-flow patterns, it was observed that while the leading-edge vortices at aspect ratios of 2.03 and 3.13 fully covered the surfaces, the vortex at an aspect ratio of 4.50 only covered up the surface approximately three times the chord, similar to that of a revolving/flapping wing. Based on the pattern at the aspect ratio of 4.50, a critical length of the leading-edge vortex of a sweptback plate was measured as ~3.1 times the chord.

The leading-edge vortex and aerodynamics of insect-based flapping-wing micro air vehicles

2009 ◽  
Vol 113 (1142) ◽  
pp. 253-262 ◽  
Author(s):  
P. C. Wilkins ◽  
K. Knowles
Keyword(s):  
Entire Range ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Flapping Wing ◽  
Computational Method ◽  
Leading Edge Vortex ◽  
Air Vehicle ◽  
Edge Vortex

AbstractThe aerodynamics of insect-like flapping are dominated by the production of a large, stable, and lift-enhancing leading-edge vortex (LEV) above the wing. In this paper the phenomenology behind the LEV is explored, the reasons for its stability are investigated, and the effects on the LEV of changing Reynolds number or angle-of-attack are studied. A predominantly-computational method has been used, validated against both existing and new experimental data. It is concluded that the LEV is stable over the entire range of Reynolds numbers investigated here and that changes in angle-of-attack do not affect the LEV’s stability. The primary motivation of the current work is to ascertain whether insect-like flapping can be successfully ‘scaled up’ to produce a flapping-wing micro air vehicle (FMAV) and the results presented here suggest that this should be the case.

Aerodynamic forces and flow structures of the leading edge vortex on a flapping wing considering ground effect

2013 ◽  
Vol 8 (3) ◽  
pp. 036007 ◽  
Author(s):  
Tien Van Truong ◽  
Doyoung Byun ◽  
Min Jun Kim ◽  
Kwang Joon Yoon ◽  
Hoon Cheol Park
Keyword(s):  
Leading Edge ◽  
Ground Effect ◽  
Flapping Wing ◽  
Flow Structures ◽  
Aerodynamic Forces ◽  
Leading Edge Vortex ◽  
Edge Vortex

ON THE PROLONG ATTACHMENT OF LEADING EDGE VORTEX ON A FLAPPING WING

2009 ◽  
Vol 23 (03) ◽  
pp. 357-360 ◽  
Author(s):  
T. T. LIM ◽  
C. J. TEO ◽  
K. B. LUA ◽  
K. S. YEO
Keyword(s):  
Constant Velocity ◽  
Leading Edge ◽  
Flapping Wing ◽  
Constant Acceleration ◽  
Leading Edge Vortex ◽  
Velocity Flow ◽  
Edge Vortex ◽  
Per Se ◽  
Spanwise Flow ◽  
Negligible Influence

In this paper, we take a fundamental approach to investigate the effect of spanwise flow on the prolonged attachment of leading edge vortex (LEV) on a flapping wing. By imposing a constant acceleration-constant velocity flow on elliptic wings of various sweep angles and angles of attack, our experimental and numerical results show that while spanwise flow per se has negligible influence on the prolong attachment of the LEV, vortex stretching can significantly delay detachment of the LEV, even for a small spanwise flow.

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.      

scholarly journals A computational fluid dynamic study of hawkmoth hovering

1998 ◽  
Vol 201 (4) ◽  
pp. 461-477 ◽  
Author(s):  
H Liu ◽  
C P Ellington ◽  
K Kawachi ◽  
C van den Berg ◽  
A P Willmott
Keyword(s):  
Fluid Dynamic ◽  
Translational Motion ◽  
Three Dimensional ◽  
Axial Flow ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Flapping Wing ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Rotational Motions

A computational fluid dynamic (CFD) modelling approach is used to study the unsteady aerodynamics of the flapping wing of a hovering hawkmoth. We use the geometry of a Manduca sexta-based robotic wing to define the shape of a three-dimensional 'virtual' wing model and 'hover' this wing, mimicking accurately the three-dimensional movements of the wing of a hovering hawkmoth. Our CFD analysis has established an overall understanding of the viscous and unsteady flow around the flapping wing and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. &lt;P&gt; A coherent leading-edge vortex with axial flow was detected during translational motions of both the up- and downstrokes. The attached leading-edge vortex causes a negative pressure region and, hence, is responsible for enhancing lift production. The axial flow, which is derived from the spanwise pressure gradient, stabilises the vortex and gives it a characteristic spiral conical shape. &lt;P&gt; The leading-edge vortex created during previous translational motion remains attached during the rotational motions of pronation and supination. This vortex, however, is substantially deformed due to coupling between the translational and rotational motions, develops into a complex structure, and is eventually shed before the subsequent translational motion. &lt;P&gt; Estimation of the forces during one complete flapping cycle shows that lift is produced mainly during the downstroke and the latter half of the upstroke, with little force generated during pronation and supination. The stroke plane angle that satisfies the horizontal force balance of hovering is 23.6 degrees , which shows excellent agreement with observed angles of approximately 20-25 degrees . The time-averaged vertical force is 40 % greater than that needed to support the weight of the hawkmoth.

The role of advance ratio and aspect ratio in determining leading-edge vortex stability for flapping flight

2014 ◽  
Vol 751 ◽  
pp. 71-105 ◽  
Author(s):  
R. R. Harbig ◽  
J. Sheridan ◽  
M. C. Thompson
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Leading Edge Vortex ◽  
Aspect Ratios ◽  
Edge Vortex ◽  
Advance Ratio ◽  
Vorticity Production ◽  
The Stability

AbstractThe effects of advance ratio and the wing’s aspect ratio on the structure of the leading-edge vortex (LEV) that forms on flapping and rotating wings under insect-like flight conditions are not well understood. However, recent studies have indicated that they could play a role in determining the stable attachment of the LEV. In this study, a numerical model of a flapping wing at insect Reynolds numbers is used to explore the effects of these parameters on the characteristics and stability of the LEV. The word ‘stability’ is used here to describe whether the LEV was attached throughout the stroke or if it was shed. It is demonstrated that increasing the advance ratio enhances vorticity production at the leading edge during the downstroke, and this results in more rapid growth of the LEV for non-zero advance ratios. Increasing the wing aspect ratio was found to have the effect of shortening the wing’s chord length relative to the LEV’s size. These two effects combined determine the stability of the LEV. For high advance ratios and large aspect ratios, the LEV was observed to quickly grow to envelop the entire wing during the early stages of the downstroke. Continued rotation of the wing resulted in the LEV being eventually shed as part of a vortex loop that peels away from the wing’s tip. The shedding of the LEV for high-aspect-ratio wings at non-zero advance ratios leads to reduced aerodynamic performance of these wings, which helps to explain why a number of insect species have evolved to have low-aspect-ratio wings.

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