Relationship between aerodynamic forces, flow structures and wing camber for rotating insect wing planforms

2013 ◽  
Vol 730 ◽  
pp. 52-75 ◽  
Author(s):  
R. R. Harbig ◽  
J. Sheridan ◽  
M. C. Thompson
Keyword(s):  
Leading Edge ◽  
Fruit Fly ◽  
Reynolds Numbers ◽  
Flow Structures ◽  
Aerodynamic Forces ◽  
Insect Wing ◽  
Deformation Parameters ◽  
Edge Vortex ◽  
Wing Deformation ◽  
Rigid Wing

AbstractWing deformation is observed during the flight of some insect species; however, the effect of these distorted wing shapes on the leading edge vortex (LEV) is not well understood. In this study, we investigate the effect of one of these deformation parameters, (rigid) wing camber, on the flow structures and aerodynamic forces for insect-like wings, using a numerical model of an altered fruit fly wing revolving at a constant angular velocity. Both positive and negative camber was investigated at Reynolds numbers of 120 and 1500, along with the chordwise location of maximum camber. It was found that negatively cambered wings produce very similar LEV structures to non-cambered wings at both Reynolds numbers, but high positive camber resulted in the formation of multiple streamwise vortices at the higher Reynolds number, which disrupt the development of the main LEV. Despite this, positively cambered wings were found to produce higher lift to drag ratios than flat or negatively cambered wings. It was determined that a region of low pressure near the wing’s leading edge, combined with the curvature of the wing’s upper surface in this region, resulted in a vertical tilting of the net force vector for positively cambered wings, which explains how insects can benefit from wing camber.

Reynolds number and aspect ratio effects on the leading-edge vortex for rotating insect wing planforms

2013 ◽  
Vol 717 ◽  
pp. 166-192 ◽  
Author(s):  
R. R. Harbig ◽  
J. Sheridan ◽  
M. C. Thompson
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Leading Edge ◽  
Fruit Fly ◽  
Flow Structures ◽  
Leeward Side ◽  
Aerodynamic Forces ◽  
Leading Edge Vortex ◽  
Wing Span ◽  
Edge Vortex

AbstractPrevious studies investigating the effect of aspect ratio ($\mathit{AR}$) for insect-like regimes have reported seemingly different trends in aerodynamic forces, however no detailed flow observations have been made. In this study, the effect of $\mathit{AR}$ and Reynolds number on the flow structures over insect-like wings is explored using a numerical model of an altered fruit fly wing revolving at a constant angular velocity. Increasing the Reynolds number for an $\mathit{AR}$ of 2.91 resulted in the development of a dual leading-edge vortex (LEV) structure, however increasing $\mathit{AR}$ at a fixed Reynolds number generated the same flow structures. This result shows that the effects of Reynolds number and $\mathit{AR}$ are linked. We present an alternative scaling using wing span as the characteristic length to decouple the effects of Reynolds number from those of $\mathit{AR}$. This results in a span-based Reynolds number, which can be used to independently describe the development of the LEV. Indeed, universal behaviour was found for various parameters using this scaling. The effect of $\mathit{AR}$ on the vortex structures and aerodynamic forces was then assessed at different span-based Reynolds numbers. Scaling the flow using the wing span was found to apply when a strong spanwise velocity is present on the leeward side of the wing and therefore may prove to be useful for similar studies involving flapping or rotating wings at high angles of attack.

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

scholarly journals UNSTEADY AERODYNAMIC PERFORMANCE OF MODEL WINGS AT LOW REYNOLDS NUMBERS

1993 ◽  
Vol 174 (1) ◽  
pp. 45-64 ◽  
Author(s):  
M. H. Dickinson ◽  
K. G. Gotz
Keyword(s):  
Insect Flight ◽  
Delta Wing ◽  
Force Production ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Aerodynamic Forces ◽  
Trailing Edge ◽  
Leading Edge Vortex ◽  
Precise Knowledge ◽  
Edge Vortex

The synthesis of a comprehensive theory of force production in insect flight is hindered in part by the lack of precise knowledge of unsteady forces produced by wings. Data are especially sparse in the intermediate Reynolds number regime (10<Re<1000) appropriate for the flight of small insects. This paper attempts to fill this deficit by quantifying the time-dependence of aerodynamic forces for a simple yet important motion, rapid acceleration from rest to a constant velocity at a fixed angle of attack. The study couples the measurement of lift and drag on a two-dimensional model with simultaneous flow visualization. The results of these experiments are summarized below. 1. At angles of attack below 13.5°, there was virtually no evidence of a delay in the generation of lift, in contrast to similar studies made at higher Reynolds numbers. 2. At angles of attack above 13.5°, impulsive movement resulted in the production of a leading edge vortex that stayed attached to the wing for the first 2 chord lengths of travel, resulting in an 80 % increase in lift compared to the performance measured 5 chord lengths later. It is argued that this increase is due to the process of detached vortex lift, analogous to the method of force production in delta-wing aircraft. 3. As the initial leading edge vortex is shed from the wing, a second vortex of opposite vorticity develops from the trailing edge of the wing, correlating with a decrease in lift production. This pattern of alternating leading and trailing edge vortices generates a von Karman street, which is stable for at least 7.5 chord lengths of travel. 4. Throughout the first 7.5 chords of travel the model wing exhibits a broad lift plateau at angles of attack up to 54°, which is not significantly altered by the addition of wing camber or surface projections. 5. Taken together, these results indicate how the unsteady process of vortex generation at large angles of attack might contribute to the production of aerodynamic forces in insect flight. Because the fly wing typically moves only 2–4 chord lengths each half-stroke, the complex dynamic behavior of impulsively started wing profiles is more appropriate for models of insect flight than are steady-state approximations.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

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.

scholarly journals Morphological diversification has led to inter-specific variation in elastic wing deformation during flight in scarab beetles

2020 ◽  
Vol 7 (4) ◽  
pp. 200277 ◽  
Author(s):  
Y. Meresman ◽  
J. F. Husak ◽  
R. Ben-Shlomo ◽  
G. Ribak
Keyword(s):  
Aerodynamic Force ◽  
Leading Edge ◽  
Dung Beetles ◽  
Food Sources ◽  
Wing Vein ◽  
Geometric Morphometric ◽  
Insect Wing ◽  
Specific Variation ◽  
Wing Deformation ◽  
Scarab Beetles

Insect wing shapes and the internal wing-vein arrangement are remarkably diverse. Although the wings lack intrinsic musculature to adjust shape actively, they elastically deform due to aerodynamic and inertial loads during flapping. In turn, the deformations alter the shape of the wing profile affecting the aerodynamic force. To determine how changes in wing-vein arrangement affect elastic wing deformation during free flight, we compared elastic wing deformations between free-flying rose chafers ( Protaetia cuprea ) and dung beetles ( Scarabaeus puncticollis ), complementing the comparison with wing static bending measurements. The broader relevance of the results to scarab beetle divergence was examined in a geometric morphometric (GM) analysis of wing-vein arrangement in 20 species differing in phylogeny and ecology. Despite rose chafers and dung beetles demonstrating similar flapping kinematics and wing size, the rose chafer wings undergo greater elastic deformation during flapping. GM analyses corrected for phylogenetic relatedness revealed that the two beetles represent extremes in wing morphology among the scarab subfamilies. Most of the differences occur at the distal leading edge and the proximal trailing edge of the wing, diversifying the flexibility of these regions, thereby changing the pattern of elastic wing deformation during flapping. Changes to local wing compliance seem to be associated with the diversification of scarab beetles to different food sources, perhaps as an adaptation to meet the demands of diverse flight styles.

scholarly journals Fruit fly scale robots can hover longer with flapping wings than with spinning wings

2016 ◽  
Vol 13 (123) ◽  
pp. 20160730 ◽  
Author(s):  
Elliot W. Hawkes ◽  
David Lentink
Keyword(s):  
Scaling Laws ◽  
Leading Edge ◽  
Fruit Fly ◽  
Flapping Wings ◽  
High Lift ◽  
Micro Robot ◽  
Actuator System ◽  
Edge Vortex ◽  
Level Analysis ◽  
Flying Robots

Hovering flies generate exceptionally high lift, because their wings generate a stable leading edge vortex. Micro flying robots with a similar wing design can generate similar high lift by either flapping or spinning their wings. While it requires less power to spin a wing, the overall efficiency depends also on the actuator system driving the wing. Here, we present the first holistic analysis to calculate how long a fly-inspired micro robot can hover with flapping versus spinning wings across scales. We integrate aerodynamic data with data-driven scaling laws for actuator, electronics and mechanism performance from fruit fly to hummingbird scales. Our analysis finds that spinning wings driven by rotary actuators are superior for robots with wingspans similar to hummingbirds, yet flapping wings driven by oscillatory actuators are superior at fruit fly scale. This crossover is driven by the reduction in performance of rotary compared with oscillatory actuators at smaller scale. Our calculations emphasize that a systems-level analysis is essential for trading-off flapping versus spinning wings for micro flying robots.

An analysis of aerodynamic forces on a delta wing

1996 ◽  
Vol 316 ◽  
pp. 173-196 ◽  
Author(s):  
Chien-Cheng Chang ◽  
Sheng-Yuan Lei
Keyword(s):  
Mach Number ◽  
Stokes Equations ◽  
Delta Wing ◽  
Leading Edge ◽  
Navier Stokes ◽  
Flow Structures ◽  
Aerodynamic Forces ◽  
Navier Stokes Equations ◽  
Lift And Drag ◽  
Secondary Vortices

The present study aims at relating lift and drag to flow structures around a delta wing of elliptic section. Aerodynamic forces are analysed in terms of fluid elements of non-zero vorticity and density gradient. The flow regime considered is Mα = 0.6 ∼ 1.8 and α = 5° ∼ 19°, where Mα denotes the free-stream Mach number and α the angle of attack. Let ρ denote the density, u velocity, and ω vorticity. It is found that there are two major source elements Re(x) and Ve(x) which contribute about 95% or even more to the aerodynamic forces for all the cases under consideration, \[R_e({\bm x})=-\frac{1}{2} {\bm u}^2 \nabla\rho \cdot \nabla\phi\quad {\rm and}\quad V_e ({\bm x}) = -\rho{\bm u}\times {\bm \omega}\cdot \nabla\phi,\] where θ is an acyclic potential, generated by the delta wing moving with unit velocity in the negative direction of the force (lift or drag). All the physical quantities are non-dimensionalized. Detailed force contributions are analysed in terms of the flow structures and the elements Re(x) and Ve(x). The source elements Re(x) and Ve(x) are concentrated in the following regions: the boundary layer in front of (below) the delta wing, the primary and secondary vortices over the delta wing, and a region of expansion around the leading edge. It is shown that Ve(x) due to vorticity prevails as the source of forces at relatively low Mach number, Mα < 0.7. Above about Mα = 0.75, Re(x) due to compressibility generally becomes the dominating contributor to the lift, while the overall contribution from Ve(x) decreases with increasing Mα, and even becomes negative at Mα = 1.2 for the lift, and at a higher Mα for the drag. The analysis is carried out with the aid of detailed numerical results by solving the Reynolds-averaged Navier–Stokes equations, which are in close agreement with experiments in comparisons of the surface pressure distributions.

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.

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