Academic literature on the topic 'Vortex-motion. Leading edges (Aerodynamics)'
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Journal articles on the topic "Vortex-motion. Leading edges (Aerodynamics)"
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Buzica, Andrei, Lisa Debschütz, Florian Knoth, and Christian Breitsamter. "Leading-Edge Roughness Affecting Diamond-Wing Aerodynamic Characteristics." Aerospace 5, no. 3 (September 19, 2018): 98. http://dx.doi.org/10.3390/aerospace5030098.
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Diamond wing configurations for low signature vehicles have been studied in recent years. Yet, despite numerous research on highly swept, sharp edged wings, little research on aerodynamics of semi-slender wings with blunt leading-edges exists. This paper reports on the stall characteristics of the AVT-183 diamond wing configuration with variation of leading-edge roughness size and Reynolds number. Wind tunnel testing applying force and surface pressure measurements are conducted and the results presented and analysed. For the investigated Reynolds number range of 2.1 × 10 6 ≤ R e ≤ 2.7 × 10 6 there is no significant influence on the aerodynamic coefficients. However, leading-edge roughness height influences the vortex separation location. Trip dots produced the most downstream located vortex separation onset. Increasing the roughness size shifts the separation onset upstream. Prior to stall, global aerodynamic coefficients are little influenced by leading-edge roughness. In contrast, maximum lift and maximum angle of attack is reduced with increasing disturbance height. Surface pressure fluctuations show dominant broadband frequency peaks, distinctive for moderate sweep vortex breakdown. The experimental work presented here provides insights into the aerodynamic characteristics of diamond wings in a wide parameter space including a relevant angle of attack range up to post-stall.
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Zhao, Hong Yan, Peng Fei Zhang, and Yun Ma. "The Influence of the Flight Aerodynamic for Interactions of Wings and Body of the Honeybee." Applied Mechanics and Materials 670-671 (October 2014): 700–704. http://dx.doi.org/10.4028/www.scientific.net/amm.670-671.700.
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The flight mechanism of flapping-wing was studied by using the translation-rotation model. We established the flapping-coordinate of the wing, gave the equation of the motion, and simplified the flapping-wing model. The aerodynamic and vortices were simulated by the CFD software of Fluent. The leading-edge vortex generated in the translation phase, and delayed stall mechanism had an important effect on the high lift. In the rotation phase, lift peaks appear due to the wing rapidly rotating and rotational circulation mechanism. The aerodynamics were obtained in different amplitudes, frequencies, angles of attack, the locations of rotating axis and timings of rotation. The influence of these parameters on average lift coefficient is obvious, while it can be ignored to average drag coefficient. Keywords: wing, aerodynamics, vortices, numerical simulation.
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Willmott, Alexander P., Charles P. Ellington, and Adrian L. R. Thomas. "Flow visualization and unsteady aerodynamics in the flight of the hawkmoth, Manduca sexta." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 352, no. 1351 (March 29, 1997): 303–16. http://dx.doi.org/10.1098/rstb.1997.0022.
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The aerodynamic mechanisms employed durng the flight of the hawkmoth, Manduca sexta , have been investigated through smoke visualization studies with tethered moths. Details of the flow around the wings and of the overall wake structure were recorded as stereophotographs and high–speed video sequences. The changes in flow which accompanied increases in flight speed from 0.4 to 5.7 m s −1 were analysed. The wake consists of an alternating series of horizontal and vertical vortex rings which are generated by successive down– and upstrokes, respectively. The downstroke produces significantly more lift than the upstroke due to a leading–edge vortex which is stabilized by a radia flow moving out towards the wingtip. The leading–edge vortex grew in size with increasing forward flight velocity. Such a phenomenon is proposed as a likely mechanism for lift enhancement in many insect groups. During supination, vorticity is shed from the leading edge as postulated in the ‘flex’ mechanism. This vorticity would enhance upstroke lift if it was recaptured diring subsequent translation, but it is not. Instead, the vorticity is left behind and the upstroke circulation builds up slowly. A small jet provides additional thrust as the trailing edges approach at the end of the upstroke. The stereophotographs also suggest that the bound circulation may not be reversed between half strokes at the fastest flight speeds.
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Viswanath, P. R., and S. R. Patil. "Aerodynamic characteristics of delta wing–body combinations at high angles of attack." Aeronautical Journal 98, no. 975 (May 1994): 159–70. http://dx.doi.org/10.1017/s0001924000049848.
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AbstractAn experimental study investigating the aerodynamic characteristics of generic delta wing-body combinations up to high angles of attack was carried out at a subsonic Mach number. Three delta wings having sharp leading edges and sweep angles of 50°, 60° and 70° were tested with two forebody configurations providing a variation of the nose fineness ratio. Measurements made included six-component forces and moments, limited static pressures on the wing lee-side and surface flow visualisation studies. The results showed symmetric flow features up to an incidence of about 25°, beyond which significant asymmetry was evident due to wing vortex breakdown, forebody vortex asymmetry or both. At higher incidence, varying degrees of forebody-wing vortex interaction effects were seen in the mean loads, which depended on the wing sweep and the nose fineness ratio. The vortex breakdown on these wings was found to be a gradual process, as implied by the wing pressures and the mean aerodynamic loads. Effects of forebody vortex asymmetry on the wing-body aerodynamics have also been assessed. Comparison of Datcom estimates with experimental data of longitudinal aerodynamic characteristics on all three wing-body combinations indicated good agreement in the symmetric flow regime.
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Saputra, Do Young Byun, Yung Hwan Byun, and Hoon Cheol Park. "Experimental and Numerical Study on Flapping Wing Kinematics and Aerodynamics of Coleoptera." Key Engineering Materials 326-328 (December 2006): 175–78. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.175.
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In this study we have experimentally and numerically analyzed the flapping mechanism and wing kinematics of coleoptera (Propylea japonica Thunberg). Using digital high speed camera, we captured the continuous wing kinematics and visualized the flight motion of the free-flying coleoptera. The experimental visualization shows that the elytra flapped concurrently with the main wing both in the downstroke and upstroke motions. In order to define the wing kinematics of coleoptera, the displacement of a wing cross section (50% span-wise) was measured for each sequence of the wing motion. Using these data, the flight motion of coleoptera was numerically simulated to investigate the aerodynamic performance. The computational aerodynamic simulation shows that leading edge vortex shedding plays a key role in generating lift to keep the insect aloft.
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Liu, H., C. P. Ellington, K. Kawachi, C. van den Berg, and A. P. Willmott. "A computational fluid dynamic study of hawkmoth hovering." Journal of Experimental Biology 201, no. 4 (February 15, 1998): 461–77. http://dx.doi.org/10.1242/jeb.201.4.461.
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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. <P> 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. <P> 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. <P> 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.
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Lamar, J. "A career in vortices and edge forces." Aeronautical Journal 116, no. 1176 (February 2012): 101–52. http://dx.doi.org/10.1017/s0001924000006667.
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Abstract This lecture recognises the background and distinguished work of Frederick William Lanchester, and notes that my background has a few similarities with his. These include a shared interest in wings, lift and vortices. My career at the NASA Langley Research Center spans the time-frame from America’s Super Sonic Transport through 2009. An early emphasis involved wind-tunnel testing of research aircraft models and the development of computer codes for subsonic aerodynamics of wing planforms. These attached-flow codes were applied to various configurations, including those with variable-sweep, dihedral, and more than one planform in both the analysis- and design-modes. These codes were used to provide a connection between leading-edge-forces and the associated additional lift on delta-wings with shed-vortex systems through the leading-edge suction analogy of Edward C. Polhamus. Subsequently, I extended the suction analogy to configurations with side-edges to predict the vortical-flow aerodynamics on complex configurations, including wing-strake combinations. These analysis codes could also be used in a design-by-analysis mode for configurations with leading-edge shed vortices. Later, I was involved in vortical-flow flight research with the F-106B and the F-16XL aircraft at cruise and maneuver conditions. Associated CFD predictions, generated by me and other members of the RTO/AVT-113 task group, have increased our understanding of the flight flow-physics measured on the F-16XL aircraft.
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Ellington, C. P. "The novel aerodynamics of insect flight: applications to micro-air vehicles." Journal of Experimental Biology 202, no. 23 (December 1, 1999): 3439–48. http://dx.doi.org/10.1242/jeb.202.23.3439.
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The wing motion in free flight has been described for insects ranging from 1 to 100 mm in wingspan. To support the body weight, the wings typically produce 2–3 times more lift than can be accounted for by conventional aerodynamics. Some insects use the fling mechanism: the wings are clapped together and then flung open before the start of the downstroke, creating a lift-enhancing vortex around each wing. Most insects, however, rely on a leading-edge vortex (LEV) created by dynamic stall during flapping; a strong spanwise flow is also generated by the pressure gradients on the flapping wing, causing the LEV to spiral out to the wingtip. Technical applications of the fling are limited by the mechanical damage that accompanies repeated clapping of the wings, but the spiral LEV can be used to augment the lift production of propellers, rotors and micro-air vehicles (MAVs). Design characteristics of insect-based flying machines are presented, along with estimates of the mass supported, the mechanical power requirement and maximum flight speeds over a wide range of sizes and frequencies. To support a given mass, larger machines need less power, but smaller ones operating at higher frequencies will reach faster speeds.
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Thielicke, William, and Eize J. Stamhuis. "The influence of wing morphology on the three-dimensional flow patterns of a flapping wing at bird scale." Journal of Fluid Mechanics 768 (March 4, 2015): 240–60. http://dx.doi.org/10.1017/jfm.2015.71.
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The effect of airfoil design parameters, such as airfoil thickness and camber, are well understood in steady-state aerodynamics. But this knowledge cannot be readily applied to the flapping flight in insects and birds: flow visualizations and computational analyses of flapping flight have identified that in many cases, a leading-edge vortex (LEV) contributes substantially to the generation of aerodynamic force. In flapping flight, very high angles of attack and partly separated flow are common features. Therefore, it is expected that airfoil design parameters affect flapping wing aerodynamics differently. Existing studies have focused on force measurements, which do not provide sufficient insight into the dominant flow features. To analyse the influence of wing morphology in slow-speed bird flight, the time-resolved three-dimensional flow field around different flapping wing models in translational motion at a Reynolds number of $22\,000<\mathit{Re}<26\,000$ was studied. The effect of several Strouhal numbers ($0.2<\mathit{St}<0.4$), camber and thickness on the flow morphology and on the circulation was analysed. A strong LEV was found on all wing types at high $\mathit{St}$. The vortex is stronger on thin wings and enhances the total circulation. Airfoil camber decreases the strength of the LEV, but increases the total bound circulation at the same time, due to an increase of the ‘conventional’ bound circulation at the inner half of the wing. The results provide new insights into the influence of airfoil shape on the LEV and force generation at low $\mathit{Re}$. They contribute to a better understanding of the geometry of vertebrate wings, which seem to be optimized to benefit from LEVs in slow-speed flight.
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Han, Jong-Seob, Jo Won Chang, and Jae-Hung Han. "The advance ratio effect on the lift augmentations of an insect-like flapping wing in forward flight." Journal of Fluid Mechanics 808 (November 3, 2016): 485–510. http://dx.doi.org/10.1017/jfm.2016.629.
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Time-varying force/moment measurements and digital particle image velocimetry (DPIV) were conducted to reveal the influence of an advance ratio $J$ on an insect-like flapping wing. A scaled-up robotic model and a servo-driven towing tank were employed to investigate nine individual $J$ cases – $J=0$ (hovering), 0.0625, 0.1250, 0.1875, 0.25, 0.50, 0.75, 1.0 and $\infty$ (gliding motion) – at a high Reynolds number ($Re\sim 10^{4}$). At $J\leqslant 0.25$, the aerodynamic forces slightly increased from those in hover ($J=0$). The centres of pressure in these cases were concentrated in the outboard section, and the leading-edge vortices (LEVs) grew more conically than those in hover. Spanwise cross-sectional DPIV indicated that the wings generated more balanced downwashes, which effectively supported the slight lift increments in this range. At $J>0.25$, a drastic force drop appeared as $J$ increased. The DPIV results in the $J=0.5$ case clearly showed a strong trailing-edge vortex on the outboard trailing edges encroaching into the upper surface, which had been occupied by the LEV for lower $J$. The LEV vorticity was noticeably weakened, and coherent substructures with substantial turbulence accompanied this vorticity. In the $J=1.0$ case, such encroachment was extended to 50 % of the section, and the LEV outboard became significantly irregular. The near-wake structures also showed that the $J=1.0$ case had the narrowest downwash area, with unstable root and tip vortices, which reflected considerable attenuation in the lift enhancements. It was of note that all of these vortical behaviours were clearly distinguishable from aspect ratio ($AR$) effects. The $J$ even played a similar role to that of the $AR$ in the Navier–Stokes equation. These findings clearly indicated that the $J$ could be an independent quantity governing the overall vortical system and lift enhancing mechanism on a flapping wing of a flapping-wing micro air vehicle.
Dissertations / Theses on the topic "Vortex-motion. Leading edges (Aerodynamics)"
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Pino, Romainville Francisco Adolfo. "The effect of adding multiple triangular vortex generators on the leading edge of a wing." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4405.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xiv, 86 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 73-76).
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Young, John Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "Numerical simulation of the unsteady aerodynamics of flapping airfoils." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2005. http://handle.unsw.edu.au/1959.4/38656.
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There is currently a great deal of interest within the aviation community in the design of small, slow-flying but manoeuvrable uninhabited vehicles for reconnaissance, surveillance, and search and rescue operations in urban environments. Inspired by observation of birds, insects, fish and cetaceans, flapping wings are being actively studied in the hope that they may provide greater propulsive efficiencies than propellers and rotors at low Reynolds numbers for such Micro-Air Vehicles (MAVs). Researchers have posited the Strouhal number (combining flapping frequency, amplitude and forward speed) as the parameter controlling flapping wing aerodynamics in cruising flight, although there is conflicting evidence. This thesis explores the effect of flapping frequency and amplitude on forces and wake structures, as well as physical mechanisms leading to optimum propulsive efficiency. Two-dimensional rigid airfoils are considered at Reynolds number 2,000 ??? 40,000. A compressible Navier-Stokes simulation is combined with numerical and analytical potential flow techniques to isolate and evaluate the effect of viscosity, leading and trailing edge vortex separation, and wake vortex dynamics. The wake structures of a plunging airfoil are shown to be sensitive to the flapping frequency independent of the Strouhal number. For a given frequency, the wake of the airfoil exhibits ???vortex lock-in??? as the amplitude of motion is increased, in a manner analogous to an oscillating circular cylinder. This is caused by interaction between the flapping frequency and the ???bluff-body??? vortex shedding frequency apparent even for streamlined airfoils at low Reynolds number. The thrust and propulsive efficiency of a plunging airfoil are also shown to be sensitive to the flapping frequency independent of Strouhal number. This dependence is the result of vortex shedding from the leading edge, and an interaction between the flapping frequency and the time for vortex formation, separation and convection over the airfoil surface. The observed propulsive efficiency peak for a pitching and plunging airfoil is shown to be the result of leading edge vortex shedding at low flapping frequencies (low Strouhal numbers), and high power requirements at large flapping amplitudes (high Strouhal numbers). The efficiency peak is governed by flapping frequency and amplitude separately, rather than the Strouhal number directly.
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Wabick, Kevin. "Leading-edge vortex development on a maneuvering wing in a uniform flow." Diss., University of Iowa, 2019. https://ir.uiowa.edu/etd/6873.
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Vortices interacting with the solid surface of aerodynamic bodies are prevalent across a broad range of geometries and applications, such as dynamic stall on wind turbine and helicopter rotors, the separated flows over flapping wings of insects, birds, formation of the vortex wakes of bluff bodies, and the lift-producing vortices formed by aircraft leading-edge extensions and delta wings. This study provides fundamental insights into the formation and evolution of such vortices by considering the leading-edge vortices formed in variations of a canonical flapping wing problem.
Specifically, the vorticity transport for three distinct maneuvers are examined, a purely rolling wing, a purely pitching wing and a rolling and pitching wing, of aspect-ratio two. Once the maneuvers are characterized, a passive bleed hole will be introduced to a purely rolling wing, to alter flow topology and vorticity transport governing the circulation on the wing.
Three-dimensional representations of the velocity and vorticity fields were obtained via plenoptic particle image velocimetry (PPIV) measurements are used to perform a vorticity flux analysis that serves to identify the sources and sinks of vorticity within the flow. Time-resolved pressure measurements were obtained from the surface of the airfoil, and used to characterize the flux of vorticity diffusing from the solid surface.
Upon characterizing all of the sources and sinks of vorticity, the circulation budget was found to be fully accounted for. Interpretation of the individual vorticity balance contributions demonstrated the Coriolis acceleration did not contribute to vorticity generation and was a correction term for the apparent vorticity. The transport characteristics varied among the three cases that were investigated. The spanwise convective contribution was signification over various spanwise locations for the pure roll case. For the pure pitch the shear layer contribution and the diffusive contribution. The circulation was dependent the pitch rate, which was evident only at the beginning of the motion, and circulation growth at later times depended only on the pitch angle.The combined pitch roll cases, the transport behavior strongly resembled that of pitch, with little evidence of roll influence, despite that the flow structure and circulation distribution on the inboard part of the wing exhibited roll-like behaviors. In the final case where the wing is pitching and rolling , the shear layer contribution was balanced by the diffusive contribution, similar to that of the pure pitch case. By adding a passive bleed hole to the purely rolling cases, it was found to alter the both the flow topology and vorticity transport.
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Koyama, Ye-Bonne. "Characterisation and aerodynamic impact of leading-edge vortices on propeller blades." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX021/document.
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Cette thèse concerne l’aérodynamique de pales d'extrémité transsonique. Ces pales sont conçues pour maximiser le rendement en croisière, tout en générant la traction requise au décollage. Elles ont des profils fins et peu cambrés, travaillant à forte incidence au décollage, ce qui peut entraîner l’apparition d’un tourbillon de bord d’attaque (TBA). Or ce TBA présente des similitudes avec les tourbillons d’apex d’aile Delta, connus pour leur capacité à générer de la portance tourbillonnaire.Cette étude consiste à examiner l’intérêt du TBA pour les performances aérodynamiques.La démarche a consisté dans un premier temps à caractériser la topologie du TBA sur une maquette représentative d’une pale d’ Open Rotor, à l'aide d'essais PIV résolus en temps et de calculs RANS k-omega SST, et à évaluer la capacité de la simulation RANS à reproduire les caractéristiques d’intérêt pour cette étude. Un algorithme a été développé afin d'estimer la contribution de ce TBA à la portance à partir du champ de pression pariétal RANS.Afin d'expliciter l'influence des paramètres géométriques et de fonctionnement de la pale sur la portance tourbillonnaire, un modèle 1D de la portance tourbillonnaire a été développé puis couplé à la méthode de l'élément de pale.Les premières comparaison de géométries à iso-traction ont montré que la portance tourbillonnaire permet de générer la traction requise au décollage avec une surface alaire plus faible. Ces résultats ouvrent de nouvelles perspectives pour la conception de géométries avec un meilleur rendement en croisièreThis thesis deals with the aerodynamic properties of propeller blades. Those blades are designed to maximise cruise efficiency, while achieving the target thrust at take-off. Their thin, low-cambered profiles must work at high incidence at take-off, which may give rise to a leading-edge vortex (LEV).The topology of this LEV looks similar to Delta wing LEVs, which are known to generate vortex lift.the aim of this study is to explore the probable impact of the LEV on lift at take-off in order to reconsider propeller blade designs. The approach first consisted in caracterising the LEV topology on a model blade representative of an Open Rotor front blade, using both Time-Resolved PIV and RANS k-omega SST calculations. The comparison between both methods demonstrated the ability of RANS calculations to reproduce the LEV characteristics of interest to this study.Then, the LEV contribution to lift was evaluated thanks to an algorithm developed to estimate vortex lift contribution from RANS wall pressure fields.In order to explicit the influence of the blade's geometrical and functioning parameters on vortex lift, a 1D vortex lift model was developed and coupled to the Blade Element Momentum Theory.The first blade geometry comparative studies at iso-thrust showed that vortex lift enables to generate target thrust at take-off with a lower blade surface. This opens new perspectives for the design of blade geometries with enhanced cruise efficiency
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Berdon, Randall. "Flow structures and aerodynamic loads of a rolling wing in a free stream." Thesis, University of Iowa, 2019. https://ir.uiowa.edu/etd/6705.
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The leading-edge vortex (LEV) is a structure found in unsteady aerodynamics that can alter the forces induced on wings and other rotating structures. This thesis presents an experimental study on LEV development on low aspect-ratio wing rolling in a uniform flow at high angles of attack. The flow structure dynamics of rotating wings in the presence of a free stream are not well understood due to the limited studies under these conditions. In this study, a broad parameter space with varying advance ratio and wing radius of gyration are analyzed using dye-visualizations. In most cases, either a conical LEV structure developed on the inboard part of the wing and persisted to a significant roll angle, as well as the arch structure. Plenoptic PIV was used to validate observations in flow visualizations as well as identify finer structures. A binary classification criterion was defined based on the formation and persistence of the inboard conical LEV structure. This criterion identified the LEV as either conical ,non-conical or transitional. Previous studies inspired the proposal of a ”rotation parameter” ,ΠRot, that was a based on a non-dimensional velocity gradient. A value of ΠRot = 0.17 was found to separate conical and non-conical LEV parameter, suggesting the fundamental importance of this parameter to LEV dynamics. Furthermore, the forces were analyzed to understand the impact of the flow structure on the forces. The conical LEVs had a transient peak followed by irregular udulations while the non-conical LEVs produced high frequency oscillations. In both cases, the force could be understood based on the time-evolution of the LEVs.
Passive bleeding was considered within this study to perturb the flow. Four passive bleed configurations were experimented with at different hole locations and sizes. It was found that a hole applied near the wing root with a large diameter perturbed the flow and transformed the structure from conical to non-conical classifications. This provides a platform to further understand the flow mechanisms that govern LEV formation and evolution by drastically changing flow structures and maintaining the same geometric and kinematic parameters. Additional studies were done analyzing the changes on the forces on the wing. The lift on the passive bleeding did not seem to be affected however, the thrust was decreased to nearly 0.
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Schaeffler, Norman Walter. "All The King's Horses: The Delta Wing Leading-Edge Vortex System Undergoing Vortex Breakdown: A Contribution to its characterization and Control under Dynamic Conditions." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30454.
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The quality of the flow over a 75 degree-sweep delta wing
was documented for steady angles of attack and during
dynamic maneuvers with and without the use of two control
surfaces. The three-dimensional velocity field over a delta
wing at a steady angle of attack of 38 degrees and Reynolds
number of 72,000 was mapped out using laser-Doppler
velocimetry over one side of the wing. The three-dimensional
streamline and vortex line distributions were visualized.
Isosurfaces of vorticity, planar distributions of helicity
and all three vorticity components, and the indicator of
the stability of the core were studied and compared to see
which indicated breakdown first. Visualization of the
streamlines and vortex lines near the core of the vortex
indicate that the core has a strong inviscid character, and
hence Reynolds number independence, upstream of breakdown,
with viscous effects becoming more important downstream of
the breakdown location. The effect of cavity flaps on the
flow over a delta wing was documented for steady angles of
attack in the range 28 degrees to 42 degrees by flow
visualization and surface pressure measurements at a
Reynolds number of 470,000 and 1,000,000, respectfully.
It was found that the cavity flaps postpone the occurrence
of vortex breakdown to higher angles of attack than can be
realized by the basic delta wing. The effect of
continuously deployed cavity flaps during a dynamic
pitch-up maneuver of a delta wing on the surface pressure
distribution were recorded for a reduced frequency of
0.0089 and a Reynolds number of 1,300,000. The effect of
deploying a set of cavity flaps during a dynamic pitch-up
maneuver on the surface pressure distribution was recorded
for a reduced frequency of 0.0089 and a Reynolds number of
1,300,000 and 187,000. The active deployment of the cavity
flaps was shown to have a short-lived beneficial effect on
the surface pressure distribution. The effect on the
surface pressure distribution of the varying the reduced
frequency at constant Reynolds number for a plain delta
wing was documented in the reduced frequency range of
0.0089 to 0.0267. The effect of the active deployment of
an apex flap during a pitch-up maneuver on the surface
pressure distribution at Reynolds numbers of 532,000,
1,000,000, and 1,390,000 were documented with reduced
frequencies of 0.0053 to 0.0114 with flap deployment
locations in the range of 21° to 36° . The apex flap
deployment was found to have a beneficial effect on the
surface pressure distribution during the maneuver and in
the post-stall regime after the maneuver is completed.Ph. D.
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Gunasekaran, Sidaard. "Relationship Between the Free Shear Layer, the Wingtip Vortex and Aerodynamic Efficiency." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1470231642.
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Frank, Spencer. "Vortex tilting and the enhancement of spanwise flow in flapping wing flight." Honors in the Major Thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/384.
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In summary the tilting mechanism helps to explain the overall flow structure and the stability of the leading edge vortex.; The leading edge vortex has been identified as the most critical flow structure for producing lift in flapping wing flight. Its stability depends on the transport of the entrained vorticity into the wake via spanwise flow. This study proposes a hypothesis for the generation and enhancement of spanwise flow based on the chordwise vorticity that results from the tilting of the leading edge vortex and trailing edge vortex. We investigate this phenomenon using dynamically scaled robotic model wings. Two different wing shapes, one rectangular and one based on Drosophila melanogaster (fruit fly), are submerged in a tank of mineral oil and driven in a flapping motion. Two separate kinematics, one of constant angular velocity and one of sinusoidal angular velocity are implemented. In order to visualize the flow structure, a novel three dimensional particle image velocimetry system is utilized. From the three dimensional information obtained the chordwise vorticity resulting from the vortex tilting is shown using isosurfaces and planar slices in the wake of the wing. It is observed that the largest spanwise flow is located in the area between the chordwise vorticity of the leading edge vortex and the chordwise vorticity of the trailing edge vortex, supporting the hypothesis that the vortex tilting enhances the spanwise flow. Additionally the LEV on the rectangular wing is found to detach at about 80% span as opposed to 60% span for the elliptical wing. Also, two distinct regions of spanwise flow, one at the base and one at the tip, are observed at the beginning of the sinusoidal kinematic, and as the velocity of the wing increases these two regions unionize into one. Lastly, the general distribution of vorticity around each wing is found to be nearly the same, indicating that different wing shapes do not greatly affect the distribution of vorticity nor stability mechanisms in flapping flight.B.S.
Bachelors
Mechanical, Materials, and Aerospace Engineering
Engineering and Computer Science
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Jaouani, Nassim. "Modelling of installation effects on the tonal noise radiated by counter-rotating open rotors." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC002.
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The Counter-Rotating Open Rotors (CROR) are identified as a possible alternative to turbofan engines for middle-range aircrafts. Providing significant fuel savings and reducing the green-house gas emissions, they may lead however to an increased noise radiation due to the absence of nacelle shielding. To properly predict the acoustic radiation of such systems is then mandatory both to reduce the source mechanisms of the isolated engine and to offer an optimal noise installation solution. Such an objective is tackled in the present thesis in two steps. In a first part, the research aims at predicting the tonal noise radiated from the first propeller of CROR mounted on the rear fuselage by means of a pylon (pusher configuration), considering both the pylon-wake and the uniform ow effects. From the Ffowcs Williams & Hawkings' formalism, three noise sources are identified. First the unsteady loading is computed using a similar procedure to the one used for the rotor-rotor wake interaction noise prediction. The velocity deficit in the pylon wake is locally expanded in two-dimensional Fourier gusts in a reference frame attached to the front rotor. The unsteady lift induced by each gust on a blade segment is calculated using a linearized analytical response function that accounts for a realistic geometry. The steady loading is the second source contribution and is evaluated using both a software based on the lifting-line theory and some numerical simulations for different reference source surfaces. Finally the thickness noise due to the blade volume displacement is included in the analysis using Isom's formulation. From the linear acoustic assumptions, all these sources modelled as equivalent acoustic dipoles rotating in a uniformly moving atmosphere are then summed to calculate the far-field noise. The whole methodology is assessed against wind-tunnel test data and reference software predictions. A parametric study considering several pylon positionings and pylon-wake configurations with blowing is performed in order to emphasize the relative contribution of the three noise sources. Secondly, the rotor- rotor wake interaction noise being recognized as the most significant contribution in isolated configuration, its modelling is completed by introducing the dynamics of the vortex occurring near the rear-rotor leading edge. A semi-analytical methodology is developed to determine a vortex attached over a at plate embedded in a uniform ow with incidence. Applied to the case of a rear blade going through a front-rotor wake, it provides a first estimate of the noise contribution of the vortexLes hélices contrarotatives constituent une alternative possible aux turboréacteurs pour les avions moyens- courriers. Réduisant significativement la consommation de carburant et les émissions de gaz à effet de serre, ils peuvent néanmoins conduire à un rayonnement sonore accru de par l'absence de carénage. Prédire correctement le rayonnement sonore de telles motorisations est donc indispensable pour réduire les mécanismes sources propres au moteur isolé ou assurer une solution d'installation acoustique optimale. Un tel objectif est abordé dans cette thèse en deux temps. Dans un premier temps, l’étude vise à prédire le bruit tonal rayonné par la première hélice d'un moteur monté à l'arrière du fuselage (configuration dite en pousseur), en considérant les effets du sillage du pylône supportant le moteur et de l'écoulement moyen. Partant du formalisme de Ffowcs Williams & Hawkings, trois sources sonores sont identifiées à cet effet. La charge instationnaire, tout d'abord, est calculée en s'appuyant sur une méthodologie similaire à celle utilisée pour la prédiction du bruit d'interaction de sillages entre les deux rotors. Le déficit de vitesse dans le sillage du mât est décomposé localement en rafales bidimensionnelles dans un repère attaché au rotor amont. La portance instationnaire induite par chaque rafale sur un segment de pale est calculée en utilisant une fonction de réponse analytique linéarisée considérant une géométrie réaliste. Deuxième contribution, la charge stationnaire est évaluée au moyen d'un logiciel s'appuyant sur la théorie de la ligne portante mais également via des simulations numériques pour différentes surfaces sources de référence. Enfin, le bruit d'épaisseur associé au déplacement du volume de la pale est inclus dans l'analyse à partir de la formulation d'Isom. D'après les hypothèses de l'acoustique linéaire, toutes ces sources modélisées comme des dipôles acoustiques tournant dans une atmosphère uniforme en mouvement sont ensuite sommées pour calculer le bruit en champ lointain. L'ensemble de la méthodologie est comparé à des données d'essai et des prédictions d'un logiciel de référence. Une étude paramétrique considérant plusieurs positionnements du pylône et des configurations avec soufflage est effectuée afin de bien mettre en évidence les contributions relatives des trois sources sonores. Dans un deuxième temps, le bruit d'interaction de sillages étant reconnu comme la contribution majoritaire en configuration isolée, sa modélisation est complétée en introduisant la dynamique du tourbillon se développant au voisinage du bord d'attaque du rotor aval. Une méthodologie semi-analytique est développée pour déterminer un tourbillon attaché au-dessus d'une plaque plane plongée dans un écoulement uniforme avec incidence. Appliquée au cas d'une pale aval traversant le sillage du rotor amont, elle fournit une première estimation de la contribution sonore du tourbillon
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Nabawy, Mostafa. "Design of insect-scale flapping wing vehicles." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/design-of-insectscale-flapping-wing-vehicles(5720b8af-a755-4c54-beb6-ba6ef1a13168).html.
Full textAbstract:
This thesis contributes to the state of the art in integrated design of insect-scale piezoelectric actuated flapping wing vehicles through the development of novel theoretical models for flapping wing aerodynamics and piezoelectric actuator dynamics, and integration of these models into a closed form design process. A comprehensive literature review of available engineered designs of miniature rotary and flapping wing vehicles is provided. A novel taxonomy based on wing and actuator kinematics is proposed as an effective means of classifying the large variation of vehicle configurations currently under development. The most successful insect-scale vehicles developed to date have used piezoelectric actuation, system resonance for motion amplification, and passive wing pitching. A novel analytical treatment is proposed to quantify induced power losses in normal hover that accounts for the effects of non uniform downwash, wake periodicity and effective flapping disc area. Two different quasi-steady aerodynamic modelling approaches are undertaken, one based on blade element analysis and one based on lifting line theory. Both approaches are explicitly linked to the underlying flow physics and, unlike a number of competing approaches, do not require empirical data. Models have been successfully validated against experimental and numerical data from the literature. These models have allowed improved insight into the role of the wing leading-edge vortex in lift augmentation and quantification of the comparative contributions of induced and profile drag for insect-like wings in hover. Theoretical aerodynamic analysis has been used to identify a theoretical solution for the optimum planform for a flapping wing in terms of chord and twist as a function of span. It is shown that an untwisted elliptical planform minimises profile power, whereas a more highly tapered design such as that found on a hummingbird minimises induced power. Aero-optimum wing kinematics for hovering are also assessed. It is shown that for efficient flight the flapping velocity should be constant whereas for maximum effectiveness the flapping velocity should be sinusoidal. For both cases, the wing pitching at stroke reversal should be as rapid as possible. A dynamic electromechanical model of piezoelectric bending actuators has been developed and validated against data obtained from experiments undertaken as part of this thesis. An expression for the electromechanical coupling factor (EMCF) is extracted from the analytical model and is used to understand the influence of actuator design variables on actuator performance. It is found that the variation in EMCF with design variables is similar for both static and dynamic operation, however for light damping the dynamic EMCF will typically be an order of magnitude greater than for static operation. Theoretical contributions to aerodynamic and electromechanical modelling are integrated into a low order design method for propulsion system sizing. The method is unique in that aside from mass fraction estimation, the underlying models are fully physics based. The transparency of the design method provides the designer with clear insight into effects of changing core design variables such as the maximum flapping amplitude, wing mass, transmission ratio, piezoelectric characteristics on the overall design solution. Whilst the wing mass is only around 10% of the actuator mass, the effective wing mass is 16 times the effective actuator mass for a typical transmission ratio of 10 and hence the wing mass dominates the inertial contribution to the system dynamics. For optimum aerodynamic effectiveness and efficiency it is important to achieve high flapping amplitudes, however this is typically limited by the maximum allowable field strength of the piezoelectric material used in the actuator.
Books on the topic "Vortex-motion. Leading edges (Aerodynamics)"
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Kogan, M. N. Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate): Under cooperative agreement NCC1-241. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1997.
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Kogan, M. N. Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate): Under cooperative agreement NCC1-241. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1997.
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Kogan, M. N. Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate). Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1997.
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Kogan, M. N. Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate): Under cooperative agreement NCC1-241. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1997.
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Terry, Ng T., Nelson Robert C. 1942-, United States. National Aeronautics and Space Administration. Scientific and Technical Information Division., University of Notre Dame. Dept. of Aerospace and Mechanical Engineering., and Ames Research Center, eds. Visualization of leading edge vortices on a series of flat plate delta wings. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Division, 1991.
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United States. National Aeronautics and Space Administration., ed. An experimental analysis of critical factors involved in the breakdown process of leading edge vortex flows. Notre Dame, Ind: Aerodynamics Laboratory, Dept. of Aerospace and Mechanical Engineering, University of Notre Dame, 1991.
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E, Reubush David, Haddad Raymond C, and United States. National Aeronautics and Space Administration. Scientific and Technical Information Program, eds. Flow field over the wing of a delta-wing fighter model with vortex control devices at Mach 0.6 to 1.2. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1992.
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E, Reubush David, Haddad Raymond C, and United States. National Aeronautics and Space Administration. Scientific and Technical Information Program., eds. Flow field over the wing of a delta-wing fighter model with vortex control devices at Mach 0.6 to 1.2. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1992.
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Leading edge vortex dynamics on a pitching delta wing: A thesis. [Notre Dame, Ind.]: Dept. of Aerospace and Mechanical Engineering, University of Notre Dame, 1990.
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E, Byrd James, Wesselmann Gary F, and United States. National Aeronautics and Space Administration. Scientific and Technical Information Program., eds. Influence of airfoil geometry on delta wing leading-edge vortices and vortex-induced aerodynamics at supersonic speeds. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1992.
Find full textBook chapters on the topic "Vortex-motion. Leading edges (Aerodynamics)"
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Yehia Zakaria, Mohamed. "Unsteady Aerodynamics of Highly Maneuvering Flyers." In Biomimetics. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.94231.
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In this chapter, a set of analytical aerodynamic models, based on potential flow, that can be used to predict the unsteady lift response during pitching maneuvers are presented and assessed. The result examines the unsteady lift coefficients experienced by a flat plate in high-amplitude pitch ramp motion. The pitch ramps are chosen based on two ramp pitch maneuvers of a maximum amplitudes of 25 and 45 degrees starting from zero degree. The aim is investigate the use of such classical models in predicting the lift dynamics compared to a full physical-based model. Among all classical methods used, the unsteady vortex lattice method (without considering the leading edge vortex) is found to be a very good predictor of the motion lift dynamic response for the 25 ° ramp angle case. However, at high pitch maneuvers (i.e.,the 45 ° ramp angle case), could preserve the response pattern with attenuated amplitudes without high computational burden. These mathematical analytical models presented in this chapter can be used to obtain a fast estimate for aircraft unsteady lift during pitch maneuvers instead of high fidelity models, especially in the early design phases.
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Cantor, Brian. "The Burgers Vector." In The Equations of Materials, 226–48. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198851875.003.0011.
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When a material is stretched beyond its elastic limit, the atoms and molecules begin to slide over each other. This is called plasticity, and is dominated by the motion of defects in the crystal structure of the material, notably line defects called dislocations. The structure and magnitude of a dislocation is defined by its Burgers vector, which is a topological constant for a given dislocation line in a given material, so there is an effective Burgers equation: b = constant. This chapter describes: the structure of edge; screw and mixed dislocations and their associated line energy; the way in which dislocations are generated and interact under stress, leading to the yield point, work hardening and a permanent set in the material; and the use during manufacturing of deformation processing, annealing, recovery and recrystallisation. Jan Burgers’ early life in Arnhem at the beginning of the 20th century is described, as are: his time as a student with the charismatic but depressive Paul Ehrenfest, who later committed suicide; his appointment as the first Professor of Aerodynamics at Technische Universiteit Delft at a time of massive growth in the aviation industry; his contributions to aerodynamic and hydrodynamic flow as well as major Dutch engineering projects such as the Zuiderzee dams and the Maas river tunnel; his growing disaffection with the commercialisation of science and its use in warfare; and his philosophical dalliance with Soviet communism and then American capitalism.
Conference papers on the topic "Vortex-motion. Leading edges (Aerodynamics)"
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Lozano, Rafael, Vrishank Raghav, and Narayanan Komerath. "Aerodynamics of a Yawed Blade in Reverse Flow." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-85947.
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The retreating blades of rotorcraft operated at high advance ratios will experience reverse flow through a sector encompassing a wide range of blade azimuth angles. There is a great deal of uncertainty in the blade aerodynamic loads under these conditions. This is a limiting factor when trying to improve the flight speed envelope of helicopters. Previous studies and work have used two-dimensional aerodynamic approaches for the reverse flow area, making the assumption that aerodynamic forces behave similar in magnitude but opposite in direction. There have been no 3-dimensional considerations being taken into account nor was vortex induced lift considered. We hypothesize that the reverse blade flow field includes phenomena similar to the formation of a leading edge vortex on highly-swept, sharp-edges delta wings. An approach is being developed to understand aerodynamic contributions to blade loading beyond linear theory, where vortex-induced lift might be significant. Rotor blades at highly yawed angles relative to the wind can be thought of as very low aspect ratio wings. Since reverse airfoils are thought of as sharp edges, theoretically it should stand that a reverse finite wing at high yawed angles could be considered as a slender delta wing. The main aim of this work is to progress towards testing this above hypothesis. Experimental data is collected from a scaled version of a rotor blade exposed to the reverse flow at various azimuth positions representing the retreating side of the disc, in a 1.07m×1.07m low turbulence wind tunnel.
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Hart, Adam, and Lawrence Ukeiley. "Unsteady Aerodynamics on a Low Aspect Ratio Flat Plate." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30846.
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The study of biological flight has shown the potential of using unsteady fluid mechanism to enhance lift and drag capabilities in low Reynolds number flight regimes. To help further the knowledge of unsteady aerodynamic fluid phenomena, a low aspect ratio flat plate is subjected to a pitching motion superimposed on a plunging motion. Variations in this motion are introduced by adding a phase lag to the pitching cycle relative to the plunge cycle. Particle Image Velocimetery (PIV) is used to measure the instantaneous velocity fields over the upper surface of the flat plate at several points in the motion cycle. These vector fields are then averaged over approximately 420 ensembles to obtain the mean velocity field at the points in the cycle. Three vortex detection algorithms are implemented to identify the center of the vortex structures created off the leading edge and track their convection downstream. Experiments show that phase lags between 75° and 90° are more prone to create organized vortex structures and convect them in close proximity to the upper surface of this low aspect ratio flat plate.
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Yin, Bo, and Guowei Yang. "Investigation of Obstacle Effects on the Aerodynamic Performance of Flapping Wings." In ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69264.
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The study of highly unsteady wing flapping includes the large scale vortices, complicated locomotion/dynamics and deformable wing structures. When flapping insects/birds approach or perch on some objects, such as ground, wall or obstacle, the solid boundary dissipates, absorbs and bounces the leading edge, trailing edge and wing tip vortices, which are generated and shed during the flapping flight. Such phenomenon creates a high pressure area, leads to cushion effect and influences the aerodynamics, stability and maneuverability significantly. This paper uses immersed boundary method (IBM) to numerically study the aerodynamic performance of flapping wing in proximity of obstacles, investigate the distance, flapping motion and wing flexibility effects and relevant symmetric/asymmetric flow patterns, research the influence of vortex generating and shedding to the lift/drag change, explore the key distance and reveal the mechanism how insects/birds adjust the flapping motion to achieve ideal flight. Such research could theoretically support the development of micro-bionic flapping wing vehicle.
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REYNOLDS, G. A., and A. A. ABTAHI. "Instabilities in Leading-Edge Vortex Development." In 5th Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1987. http://dx.doi.org/10.2514/6.1987-2424.
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Mitchell, Anthony, Pascal Molton, Didier Barberis, and Jean Delery. "Control of leading-edge vortex breakdown by trailing edge injection." In 17th Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1999. http://dx.doi.org/10.2514/6.1999-3202.
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LEMAY, S., S. BATILL, and R. NELSON. "Leading edge vortex dynamics on a pitching delta wing." In 6th Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1988. http://dx.doi.org/10.2514/6.1988-2559.
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Limacher, Eric J., and David E. Rival. "On the Stable Leading Edge Vortex in Rotating Systems." In 32nd AIAA Applied Aerodynamics Conference. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2014. http://dx.doi.org/10.2514/6.2014-2700.
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Huang, X., Y. Sun, E. Hanff, X. Huang, Y. Sun, and E. Hanff. "Further investigations of leading-edge vortex breakdown over delta wings." In 15th Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1997. http://dx.doi.org/10.2514/6.1997-2263.
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O'NEIL, P., R. BARNETT, and C. LOUIE. "Numerical simulation of leading-edge vortex breakdown using an Eulercode." In 7th Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1989. http://dx.doi.org/10.2514/6.1989-2189.
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van Noordenburg, M., and H. Hoejmakers. "Compressible inviscid flow solutions for isolated leading-edge vortex cores." In 16th AIAA Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1998. http://dx.doi.org/10.2514/6.1998-2528.
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