Journal articles: 'Wingtip Vortices'

1

Zhang, M., Y. K. Wang, and S. Fu. "Generation Mechanism and Reduction Method of Induced Drag Produced by Interacting Wingtip Vortex System." Journal of Mechanics 34, no. 2 (September 14, 2017): 231–41. http://dx.doi.org/10.1017/jmech.2017.76.

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AbstractThe formation and evolution of wingtip vortex system generated from three wing configurations are simulated with the improved delayed detached eddy simulation (IDDES) method. Numerical results show that each layout produces an interacting wingtip vortex system. These three corresponding vortical interactions are, respectively, the interaction between wingtip vortex and its counter-rotating vortex, winglet-tip vortex, and winglet four-vortex system. The fluid entrainment of ambient fluid and vortical impulse transport resulted from inductive effect have been founded generally existing in its formation and evolution. These two dominated mechanisms account for induced drag generation. On one hand, the winglet with toed-out angle is considered capable of changing the flow field around the winglet, and decomposing the winglet-tip vortex into four small vortices. Due to quite few fluid entrainment effects, this typical four-vortex system that cannot merge and only dissipate in the near wake scarcely contributes to the induced drag. On the other hand, a potential drag reduction method is also indicated that a lower induced drag can be obtained when the merger of wingtip and winglet-tip vortex is controlled and eliminated. This investigation will offer a novel perspective to guide the design of wingtip device and method of crusing resistance reduction for aircrafts.

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Marshall, R. E., and T. J. Myers. "Wingtip generated wake vortices as radar target." IEEE Aerospace and Electronic Systems Magazine 11, no. 12 (1996): 27–30. http://dx.doi.org/10.1109/62.544796.

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3

Liu, Y. C., and F. B. Hsiao. "Aerodynamic Investigations of Low-Aspect-Ratio Thin Plate Wings at Low Reynolds Numbers." Journal of Mechanics 28, no. 1 (March 2012): 77–89. http://dx.doi.org/10.1017/jmech.2012.8.

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ABSTRACTTo realize the relationship between flow structures of wingtip vortices and post stall characteristics of low aspect-ratio wings, this paper experimentally studies the aerodynamic characteristics and the corresponding flow structures of the rectangular thin-plate wings at Reynolds numbers between 104 and 105. The aerodynamic properties to be studied include lift, drag, slopes at linear and nonlinear range of the lift curves and lift-to-drag ratios of the tested wings with the aspect ratio varying from 1.0 to 3.0. The flow structures regarding the leading-edge separation vortices and wingtip vortices at upper surface and near-wake regions of the wings are also investigated by smoke-wire visualization. Results indicate that the high stall angle of attack and vortex lift are clearly manifested to induce the nonlinear increase in the lift curves as the aspect ratio reaches less than 1.6. This phenomenon is specifically observed to augment the aerodynamic properties with the decrease of the aspect ratio. Additionally, the corresponding flow visualization also indicates that the wingtip vortices and the areas of highly affected regions are duly increased with the increase of the angle of attack up to 40°, which makes certain that the extra increase of the nonlinear lift results from these vortices. This result can be practically applied to the planform design for unmanned aerial vehicles.

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Kasmai, N., D. Thompson, E. Luke, M. Jankun-Kelly, and R. Machiraju. "Feature-based adaptive mesh refinement for wingtip vortices." International Journal for Numerical Methods in Fluids 66, no. 10 (March 23, 2010): 1274–94. http://dx.doi.org/10.1002/fld.2312.

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5

Zaccara, Mirko, Gerardo Paolillo, Carlo Salvatore Greco, Tommaso Astarita, and Gennaro Cardone. "Flow control of wingtip vortices through synthetic jets." Experimental Thermal and Fluid Science 130 (January 2022): 110489. http://dx.doi.org/10.1016/j.expthermflusci.2021.110489.

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Liu, Zhi Rong, Jun Wei Wang, and Rui Zhu. "Fluid Experimental Research on Dual-Vortex Interaction Instability." Advanced Materials Research 459 (January 2012): 195–98. http://dx.doi.org/10.4028/www.scientific.net/amr.459.195.

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A series of dual-vortex fulid visualization and interaction instability experiments are undertaken with PIV (Particle Image Velocimetry) system under various experimental parameters sets. The motion characteristics and the circulation-time curves of the dual-vortex are presented through PIV processing and analysis. The dual-vortex distance b=50mm, main wingtip angle α1=10° & side wingtip angle α2=8° are optimum experimental parameters for vortices dissipation, the most vortex strength is reduced by 30%-40%

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7

Barber, T., and P. Kurts. "Downstream evolution of wingtip vortices produced from an inverted wing." Aeronautical Journal 119, no. 1216 (June 2015): 747–63. http://dx.doi.org/10.1017/s0001924000010800.

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AbstractCounter-rotating vortices form from the opposite edges of lifting surfaces, and gradually move laterally and dissipate as they travel downstream (as seen in a wing-fixed reference frame). Under ground effect conditions, the vortex from a lifting wing – such as that used in an aircraft application – moves laterally outboard from the wingtip as it progresses downstream; for a downforce wing in ground effect – such as that used in an automotive application – the vortex moves laterally inboard. An interesting case is the situation where the inboard moving vortices become in close proximity to each other. The objective of the present study was to investigate counter-rotating vortices produced from a low aspect ratio downforce wing operating in ground effect. The pair of vortices move towards each other and mutually induce an upwards directed motion which in turn reduces the inboard movement driven by the ground effect. Experimental data gained from three-dimensional Laser Doppler Anemometry in a moving ground wind-tunnel was used to validate a Large Eddy Simulation computational result.

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Henningsson, P., F. T. Muijres, and A. Hedenström. "Time-resolved vortex wake of a common swift flying over a range of flight speeds." Journal of The Royal Society Interface 8, no. 59 (December 3, 2010): 807–16. http://dx.doi.org/10.1098/rsif.2010.0533.

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The wake of a freely flying common swift ( Apus apus L.) is examined in a wind tunnel at three different flight speeds, 5.7, 7.7 and 9.9 m s −1 . The wake of the bird is visualized using high-speed stereo digital particle image velocimetry (DPIV). Wake images are recorded in the transverse plane, perpendicular to the airflow. The wake of a swift has been studied previously using DPIV and recording wake images in the longitudinal plane, parallel to the airflow. The high-speed DPIV system allows for time-resolved wake sampling and the result shows features that were not discovered in the previous study, but there was approximately a 40 per cent vertical force deficit. As the earlier study also revealed, a pair of wingtip vortices are trailing behind the wingtips, but in addition, a pair of tail vortices and a pair of ‘wing root vortices’ are found that appear to originate from the wing/body junction. The existence of wing root vortices suggests that the two wings are not acting as a single wing, but are to some extent aerodynamically detached from each other. It is proposed that this is due to the body disrupting the lift distribution over the wing by generating less lift than the wings.

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9

Carlson, Bailey, Al Habib Ullah, and Jordi Estevadeordal. "Experimental Investigation of Vortex-Tube Streamwise-Vorticity Characteristics and Interaction Effects with a Finite-Aspect-Ratio Wing." Fluids 5, no. 3 (July 24, 2020): 122. http://dx.doi.org/10.3390/fluids5030122.

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An experimental study is conducted to analyze a streamwise-oriented vortex and investigate the unsteady interaction with a finite-aspect-ratio wing. A pressurized vortex tube is used to generate streamwise vortices in a wind tunnel and the resulting flow behavior is analyzed. The vortex tube, operated at various pressures, yields flows that evolve downstream under several freestream wind tunnel speeds. Flow measurements are performed using two- and three- dimensional (2D and 3D) particle image velocimetry to observe vortices and their freestream interactions from which velocity and vorticity data are comparatively analyzed. Results indicate that vortex velocity greater than freestream flow velocity is a primary factor in maintaining vortex structures further downstream, while increased supply pressure and reduced freestream velocity also reduce vortex dissipation rate. The generated streamwise-oriented vortex is also impinged on a finite-aspect-ratio airfoil wing with a cross-section of standard NACA0012 airfoil. The wingtip-aligned vortex is shown to investigate the interaction of the streamwise vortex and the wingtip vortex region. The results indicate that the vorticity at the high vortex-tube pressure has a significant effect on the boundary layer of airfoil.

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Inasawa, Ayumu, Fumihide Mori, and Masahito Asai. "Detailed Observations of Interactions of Wingtip Vortices in Close-Formation Flight." Journal of Aircraft 49, no. 1 (January 2012): 206–13. http://dx.doi.org/10.2514/1.c031480.

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11

Dufhaus, Sebastian, Sarina Brautmeier, Anna Uhl, Ralf Hörnschemeyer, and Eike Stumpf. "Modal analysis of wingtip vortices by means of Proper Orthogonal Decomposition." PAMM 17, no. 1 (December 2017): 693–94. http://dx.doi.org/10.1002/pamm.201710315.

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12

Gerz, T., and T. Ehret. "Wingtip vortices and exhaust jets during the jet regime of aircraft wakes." Aerospace Science and Technology 1, no. 7 (October 1997): 463–74. http://dx.doi.org/10.1016/s1270-9638(97)90008-0.

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13

Mi, Bai-gang, and Hao Zhan. "Numerical Simulation of the Static and Dynamic Aerodynamics of a UAV under Wake Flows." Journal of Advanced Transportation 2019 (April 1, 2019): 1–12. http://dx.doi.org/10.1155/2019/6326794.

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Frequent flight conflicts will be observed as the number of aircrafts increases, and such conflicts will cause unprecedented challenges in flight safety; thus, the flight characteristics of small aircrafts under the wake flow of a large airliner should be thoroughly analyzed. Combined with the sliding mesh technique, a computational fluid dynamics (CFD) method is proposed in this paper to simulate three wake flow patterns, i.e., wingtip vortex, jet flow, and propeller slipstream, and then, the static and dynamic derivatives that represent the stability of the fly wing under the wake flow are identified by using the least squares method. The results demonstrate that both the steady and unsteady aerodynamics of the fly wing are affected by wake flows: wingtip vortices increase the lift-to-drag ratio and considerably change the dynamic damping; jet flow reduces both the static and dynamic damping; and propeller slipstream leads to slow variations in the dynamic damping and decreases in the lift-to-drag ratio.

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14

Panagiotou, Pericles, George Ioannidis, Ioannis Tzivinikos, and Kyros Yakinthos. "Experimental Investigation of the Wake and the Wingtip Vortices of a UAV Model." Aerospace 4, no. 4 (November 1, 2017): 53. http://dx.doi.org/10.3390/aerospace4040053.

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15

Ogawa, Shigeru, and Yusuke Kimura. "Performance Improvement by Control of Wingtip Vortices for Vertical Axis Type Wind Turbine." Open Journal of Fluid Dynamics 08, no. 03 (2018): 331–42. http://dx.doi.org/10.4236/ojfd.2018.83021.

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16

Barber, Tracie. "Visualisation of wingtip vortices produced by a wing near a stationary ground plane." International Journal of Aerodynamics 1, no. 1 (2010): 18. http://dx.doi.org/10.1504/ijad.2010.031699.

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17

Craft, T. J., A. V. Gerasimov, B. E. Launder, and C. M. E. Robinson. "A computational study of the near-field generation and decay of wingtip vortices." International Journal of Heat and Fluid Flow 27, no. 4 (August 2006): 684–95. http://dx.doi.org/10.1016/j.ijheatfluidflow.2006.02.024.

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18

KleinHeerenbrink, Marco, L. Christoffer Johansson, and Anders Hedenström. "Multi-cored vortices support function of slotted wing tips of birds in gliding and flapping flight." Journal of The Royal Society Interface 14, no. 130 (May 2017): 20170099. http://dx.doi.org/10.1098/rsif.2017.0099.

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Slotted wing tips of birds are commonly considered an adaptation to improve soaring performance, despite their presence in species that neither soar nor glide. We used particle image velocimetry to measure the airflow around the slotted wing tip of a jackdaw ( Corvus monedula ) as well as in its wake during unrestrained flight in a wind tunnel. The separated primary feathers produce individual wakes, confirming a multi-slotted function, in both gliding and flapping flight. The resulting multi-cored wingtip vortex represents a spreading of vorticity, which has previously been suggested as indicative of increased aerodynamic efficiency. Considering benefits of the slotted wing tips that are specific to flapping flight combined with the wide phylogenetic occurrence of this configuration, we propose the hypothesis that slotted wings evolved initially to improve performance in powered flight.

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19

Feys, J., and S. A. Maslowe. "Elliptical instability of the Moore–Saffman model for a trailing wingtip vortex." Journal of Fluid Mechanics 803 (August 30, 2016): 556–90. http://dx.doi.org/10.1017/jfm.2016.512.

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In this paper, we investigate the elliptical instability exhibited by two counter-rotating trailing vortices. This type of instability can be viewed as a resonance between two normal modes of a vortex and an external strain field. Recent numerical investigations have extended earlier results that ignored axial flow to include models with a simple wake-like axial flow such as the similarity solution found by Batchelor (J. Fluid Mech., vol. 20, 1964, pp. 645–658). We present herein growth rates of elliptical instability for a family of velocity profiles found by Moore & Saffman (Proc. R. Soc. Lond. A, vol. 333, 1973, pp. 491–508). These profiles have a parameter $n$ that depends on the wing loading. As a result, unlike the Batchelor vortex, they are capable of modelling both the jet-like and the wake-like axial flow present in a trailing vortex at short and intermediate distances behind a wingtip. Direct numerical simulations of the linearized Navier–Stokes equations are performed using an efficient spectral method in cylindrical coordinates developed by Matsushima & Marcus (J. Comput. Phys., vol. 53, 1997, pp. 321–345). We compare our results with those for the Batchelor vortex, whose velocity profiles are closely approximated as the wing loading parameter $n$ approaches 1. An important conclusion of our investigation is that the stability characteristics vary considerably with $n$ and $W_{0}$, a parameter measuring the strength of the mean axial velocity component. In the case of an elliptically loaded wing ($n=0.50$), we find that the instability growth rates are up to 50 % greater than those for the Batchelor vortex. Our results demonstrate the significant effect of the distribution and intensity of the axial flow on the elliptical instability of a trailing vortex.

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20

García-Ortiz, J. Hermenegildo, A. Domínguez-Vázquez, J. J. Serrano-Aguilera, L. Parras, and C. del Pino. "A complementary numerical and experimental study of the influence of Reynolds number on theoretical models for wingtip vortices." Computers & Fluids 180 (February 2019): 176–89. http://dx.doi.org/10.1016/j.compfluid.2018.12.009.

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21

PARKER, K., K. D. VON ELLENRIEDER, and J. SORIA. "Morphology of the forced oscillatory flow past a finite-span wing at low Reynolds number." Journal of Fluid Mechanics 571 (January 4, 2007): 327–57. http://dx.doi.org/10.1017/s0022112006003491.

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A study of the morphology of the vortical skeleton behind a flapping NACA0030 wing with a finite aspect ratio of 3, is undertaken. The motivation for this work originates with the proposal that thrust can be efficiently produced by flapping aerofoils. The test condition corresponds to a Strouhal number of 0.35, Reynolds number, based on aerofoil chord, of 600 and an amplitude of flapping, equal to the chord length of the wing. This test condition corresponds to the optimal thrust-producing case in infinite-span flapping wings. This study investigates the effect of wing three-dimensionality on the structure of the wake-flow. This is accomplished here, by quantitatively describing the spatio-temporal variations in the velocity, vorticity and Reynolds stresses for the finite-span-wing case.Preliminary flow visualizations suggest that the presence of wingtip vortices for the three-dimensional-wing case, create a different vortical structure to the two-dimensional-wing case. In the case of a two-dimensional-wing, the flow is characterized by the interaction of leading- and trailing-edge vorticity, resulting in the formation of a clear reverse Kármán vortex street at the selected test condition. In the case of a three-dimensional-wing, the flow exhibits a high degree of complexity and three-dimensionality, particularly in the midspan region. Using phase-averaged particle image velocimetry measurements of the forced oscillatory flow, a quantitative analysis in the plane of symmetry of the flapping aerofoil was undertaken. Using a triple decomposition of the measured velocities, the morphological characteristics of the spanwise vorticity is found to be phase correlated with the aerofoil kinematics. Reynolds stresses in the direction of oscillation are the dominant dissipative mechanism. The mean velocity profiles resemble a jet, indicative of thrust production. Pairs of strong counter-rotating vortices from the leading- and trailing-edge of the aerofoil are shed into the flow at each half-cycle. The large-scale structure of the flow is characterized by constructive merging of spanwise vorticity. The midspan region is populated by cross-sections of interconnected vortex rings.

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Edstrand, Adam M., Peter J. Schmid, Kunihiko Taira, and Louis N. Cattafesta. "A parallel stability analysis of a trailing vortex wake." Journal of Fluid Mechanics 837 (January 5, 2018): 858–95. http://dx.doi.org/10.1017/jfm.2017.866.

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Trailing vortices are generated in aeronautical and maritime applications and produce a variety of adverse effects that remain difficult to control. A stability analysis can direct flow control designers towards pertinent frequencies, wavelengths and locations that may lead to the excitation of instabilities, resulting in the eventual breakup of the vortex. Most models for trailing vortices, however, are far-field models, making implementation of the findings from stability analyses challenging. As such, we perform a stability analysis in the formative region where the numerically computed base flow contains both a two-dimensional wake and a tip vortex generated from a NACA0012 at a$5^{\circ }$angle of attack and a chord-based Reynolds number of$Re_{c}=1000$. The parallel temporal and spatial analyses show that at three chord lengths downstream of the trailing edge, seven unstable modes are present: three stemming from the temporal analysis and four arising in the spatial analysis. The three temporal instabilities are analogues to three unstable modes in the spatial analysis, with the wake instability dominating in both analyses. The helical mode localized to the vortex co-rotates with the base flow, which is converse with the counter-rotating$m=-1$instabilities of a Batchelor vortex model, which may be a result of the formative nature of the base-flow vortex. The fourth spatial mode is localized to the tip vortex region. The continuous part of the spectrum contains oscillatory and wavepacket solutions prompting the utilization of a wavepacket analysis to analyse the flow field and group velocity. The structure and details of the full bi-global spectrum will help navigate the design space of effective control strategies to hasten decay of persistent wingtip vortices.

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Wolf, M., V. M. Ortega-Jimenez, and R. Dudley. "Structure of the vortex wake in hovering Anna's hummingbirds ( Calypte anna )." Proceedings of the Royal Society B: Biological Sciences 280, no. 1773 (December 22, 2013): 20132391. http://dx.doi.org/10.1098/rspb.2013.2391.

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Hummingbirds are specialized hoverers for which the vortex wake has been described as a series of single vortex rings shed primarily during the downstroke. Recent findings in bats and birds, as well as in a recent study on Anna's hummingbirds, suggest that each wing may shed a discrete vortex ring, yielding a bilaterally paired wake. Here, we describe the presence of two discrete rings in the wake of hovering Anna's hummingbirds, and also infer force production through a wingbeat with contributions to weight support. Using flow visualization, we found separate vortices at the tip and root of each wing, with 15% stronger circulation at the wingtip than at the root during the downstroke. The upstroke wake is more complex, with near-continuous shedding of vorticity, and circulation of approximately equal magnitude at tip and root. Force estimates suggest that the downstroke contributes 66% of required weight support, whereas the upstroke generates 35%. We also identified a secondary vortex structure yielding 8–26% of weight support. Lift production in Anna's hummingbirds is more evenly distributed between the stroke phases than previously estimated for Rufous hummingbirds, in accordance with the generally symmetric down- and upstrokes that characterize hovering in these birds.

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Johansson, L. Christoffer, Sophia Engel, Emily Baird, Marie Dacke, Florian T. Muijres, and Anders Hedenström. "Elytra boost lift, but reduce aerodynamic efficiency in flying beetles." Journal of The Royal Society Interface 9, no. 75 (May 16, 2012): 2745–48. http://dx.doi.org/10.1098/rsif.2012.0053.

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Flying insects typically possess two pairs of wings. In beetles, the front pair has evolved into short, hardened structures, the elytra, which protect the second pair of wings and the abdomen. This allows beetles to exploit habitats that would otherwise cause damage to the wings and body. Many beetles fly with the elytra extended, suggesting that they influence aerodynamic performance, but little is known about their role in flight. Using quantitative measurements of the beetle's wake, we show that the presence of the elytra increases vertical force production by approximately 40 per cent, indicating that they contribute to weight support. The wing-elytra combination creates a complex wake compared with previously studied animal wakes. At mid-downstroke, multiple vortices are visible behind each wing. These include a wingtip and an elytron vortex with the same sense of rotation, a body vortex and an additional vortex of the opposite sense of rotation. This latter vortex reflects a negative interaction between the wing and the elytron, resulting in a single wing span efficiency of approximately 0.77 at mid downstroke. This is lower than that found in birds and bats, suggesting that the extra weight support of the elytra comes at the price of reduced efficiency.

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Sy, Miguel Sumait, Binoe Eugenio Abuan, and Louis Angelo Macapili Danao. "Aerodynamic Investigation of a Horizontal Axis Wind Turbine with Split Winglet Using Computational Fluid Dynamics." Energies 13, no. 18 (September 22, 2020): 4983. http://dx.doi.org/10.3390/en13184983.

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Wind energy is one of the fastest growing renewable energy sources, and the most developed energy extraction device that harnesses this energy is the Horizontal Axis Wind Turbine (HAWT). Increasing the efficiency of HAWTs is one important topic in current research with multiple aspects to look at such as blade design and rotor array optimization. This study looked at the effect of wingtip devices, a split winglet, in particular, to reduce the drag induced by the wind vortices at the blade tip, hence increasing performance. Split winglet implementation was done using computational fluid dynamics (CFD) on the National Renewable Energy Lab (NREL) Phase VI sequence H. In total, there are four (4) blade configurations that are simulated, the base NREL Phase VI sequence H blade, an extended version of the previous blade to equalize length of the blades, the base blade with a winglet and the base blade with split winglet. Results at wind speeds of 7 m/s to 15 m/s show that adding a winglet increased the power generation, on an average, by 1.23%, whereas adding a split winglet increased it by 2.53% in comparison to the extended blade. The study also shows that the increase is achieved by reducing the drag at the blade tip and because of the fact that the winglet and split winglet generating lift themselves. This, however, comes at a cost, i.e., an increase in thrust of 0.83% and 2.05% for the blades with winglet and split winglet, respectively, in comparison to the extended blade.

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Cheng, Ze-Peng, Yang Xiang, and Hong Liu. "Experimental investigation on the structures and induced drag of wingtip vortices for different wingtip configurations." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, August 5, 2020, 095441002094791. http://dx.doi.org/10.1177/0954410020947911.

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As an effective method to reduce induced drag and the risk of wake encounter, the winglet has been an essential device and developed into diverse configurations. However, the structures and induced drag, as well as wandering features of the wingtip vortices ( WTVs) generated by these diverse winglet configurations are not well understood. Thus, the WTVs generated by four typical wingtip configurations, namely the rectangular wing with blended/raked/split winglet and without winglet (Model BL/ RA/ SP/NO for short), are investigated in this paper using particle image velocimetry technology. Comparing with an isolated primary wingtip vortex generated by Model NO, multiple vortices are twisted coherently after installing the winglets. In addition, the circulation evolution of WTVs demonstrates that the circulation for Model SP is the largest, while Model RA is the smallest. By tracking the instantaneous vortex center, the vortex wandering behavior is observed. The growth rate of wandering amplitude along with the streamwise location from the quickest to the slowest corresponds to Model SP, Model NO, Model BL, Model RA in sequence, implying that the WTVs generated by model SP exhibit the quickest mitigation. Considering that the induced drag scales as the lift to power 2, the induced drag and lift are estimated based on the wake integration method, and then the form factor λ, defined by [Formula: see text], is calculated to evaluate the aerodynamic performance. Comparing with the result of Model NO, the form factor decreases by 7.99%, 4.80%, and 2.60% for Model RA, Model BL, Model SP, respectively. In sum, Model RA and BL have a smaller induced drag coefficient but decay slower; while Model SP has a larger induced drag coefficient but decays quicker. An important implication of these results is that reducing the strength of WTVs and increasing the growth rate of vortex wandering amplitude can be the mutual requirements for designing new winglets.

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Mishra, Nishant, Anand Sagar Gupta, Jishnav Dawar, Alok Kumar, and Santanu Mitra. "Numerical and Experimental Study on Performance Enhancement of Darrieus Vertical Axis Wind Turbine With Wingtip Devices." Journal of Energy Resources Technology 140, no. 12 (July 2, 2018). http://dx.doi.org/10.1115/1.4040506.

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Darrieus type vertical axis wind turbines (VAWT) are being used commercially nowadays; however, they still need to improve in terms of performance as they work in an urban environment where the wind speeds are low and the gusts are frequent. The aerodynamic performance of Darrieus turbine is highly affected by the wingtip vortices. This paper attempts at analyzing and comparing the performance of Darrieus with the use of various wingtip devices. Attempts have also been made to find out optimal working parameters by studying the flow through turbines with different tip speed ratios and different inlet wind speeds. A comparative computational fluid dynamics (CFD) simulation was performed on a small-scale, straight-bladed Darrieus rotor vertical axis wind turbine, with a large stationary domain and a small rotating subdomain using sliding mesh technique. Comparison of the performance of end tip device that can be used against a baseline rotor configuration is done, with the aim of identifying the best tip architecture. The main focus lies on building an experimental setup to validate the results obtained with the CFD simulation and to compare the performance with and without wingtip device. VAWTs with wingtip device show very promising results compared to the baseline model.

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"Experiment on Wingtip Vortices using a Half Deltawing at the Tips." International Journal of Recent Technology and Engineering 8, no. 2S8 (September 17, 2019): 1633–38. http://dx.doi.org/10.35940/ijrte.b1119.0882s819.

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The counter rotating wing tip vortices produced by the aircraft continues to be a big concern for the aviation industry and the aircraft manufacturers due to its hazardous effects on the flight safety and aircraft efficiency. The strength of the vortices poses severe problems to the aircraft operations. Manufacturers developed various wingtip devices to alleviate this problem, but still it is not fully understood and solved. In this thesis, the effectiveness of using a half delta wing at the tips is investigated. The flow field over a low aspect ratio NACA 0015 wing fitted with a slender sharp half delta wing with a leading edge sweep angle 700 at a Reynolds number 1.87 ×105 is investigated. Particle image velocimetry is used to quantify the vortex structure and force balance measurements are used to calculate the aerodynamic data of the wing. The peak vorticity, peak tangential velocity are decreased due to the addition of half delta wing. The over-all radius of the wingtip vortex increased showing a diffused vortex due to the addition of the half delta wing. The core circulation is decreased leading to a lower strength vortex. Though the tip device increased the drag, it increases the aerodynamic efficiency through the improvement in L/D.

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Loewenthal, Ethan, and Ashok Gopalarathnam. "Low-Order Modeling of Wingtip Vortices in a Vortex Lattice Method." AIAA Journal, September 25, 2021, 1–13. http://dx.doi.org/10.2514/1.j060654.

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30

"Experimental Research on Wingtip Vortices using a Half Deltawing at the Tips." International Journal of Recent Technology and Engineering 8, no. 2S11 (November 2, 2019): 2267–72. http://dx.doi.org/10.35940/ijrte.b1250.0982s1119.

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The counter rotating wing tip vortices produced by the aircraft continues to be a big concern for the aviation industry and the aircraft manufacturers due to its hazardous effects on the flight safety and aircraft efficiency. The strength of the vortices poses severe problems to the aircraft operations. Manufacturers developed various wingtip devices to alleviate this problem, but still it is not fully understood and solved. In this thesis, the effectiveness of using a half delta wing at the tips is investigated. The flow field over a low aspect ratio NACA 0015 wing fitted with a slender sharp half delta wing with a leading edge sweep angle 700 at a Reynolds number 1.87 ×105 is investigated. Particle image velocimetry is used to quantify the vortex structure and force balance measurements are used to calculate the aerodynamic data of the wing. The peak vorticity, peak tangential velocity are decreased due to the addition of half delta wing. The over-all radius of the wingtip vortex increased showing a diffused vortex due to the addition of the half delta wing. The core circulation is decreased leading to a lower strength vortex. Though the tip device increased the drag, it increases the aerodynamic efficiency through the improvement in L/D

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31

Beves, Christopher C., and Tracie J. Barber. "The Wingtip Vortex of a Dimpled Wing With an Endplate." Journal of Fluids Engineering 139, no. 2 (November 3, 2016). http://dx.doi.org/10.1115/1.4034525.

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Dimples used as sub-boundary layer vortex generators have been shown to reduce wake size at large angles of incidence. The effect these dimples have on wingtip vortices with an endplate is measured via laser Doppler anemometry (LDA) on an inverted Tyrrell026 airfoil (ReC = 0.5 × 105 and chord = 0.075 m) in ground effect in order to determine the flow characteristics for this configuration and to see if previous measurements were performed in a thinner part of the wake due to any potential wake waviness. The strength of the wingtip vortex for the dimpled wing is 10% higher than the “clean” wing immediately downstream. The clean wing has large region of high turbulence throughout the wake, and the dimples reduce this by 50%. The net result is that dimples drastically improve the flow in the wake of the wing and endplate.

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Serrano-Aguilera, J. J., J. Hermenegildo García-Ortiz, A. Gallardo-Claros, L. Parras, and C. del Pino. "Experimental characterization of wingtip vortices in the near field using smoke flow visualizations." Experiments in Fluids 57, no. 8 (August 2016). http://dx.doi.org/10.1007/s00348-016-2222-9.

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Qin, Suyang, Zifeng Weng, Zhuoqi Li, Yang Xiang, and Hong Liu. "On the controlled evolution for wingtip vortices of a flapping wing model at bird scale." Aerospace Science and Technology, December 2020, 106460. http://dx.doi.org/10.1016/j.ast.2020.106460.

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Sibilski, K. "Dynamics of Micro-Air-Vehicle with Flapping Wings." Acta Polytechnica 44, no. 2 (January 2, 2004). http://dx.doi.org/10.14311/526.

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Small (approximately 6 inch long, or hand-held) reconnaissance micro air vehicles (MAVs) will fly inside buildings, and require hover for observation, and agility at low speeds to move in confined spaces. For this flight envelope insect-like flapping wings seem to be an optimal mode of flying. Investigation of the aerodynamics of flapping wing MAVs is very challenging. The problem involves complex unsteady, viscous flow (mainly laminar), with the moving wing generating vortices and interacting with them. At this early stage of research only a preliminary insight into the nature of the little known aerodynamics of MAVs has been obtained. This paper describes computational models for simulation of the controlled motion of a microelectromechanical flying insect – entomopter. The design of software simulation for entomopter flight (SSEF) is presented. In particular, we will estimate the flight control algorithms and performance for a Micromechanical Flying Insect (MFI), a 80–100 mm (wingtip-to-wingtip) device capable of sustained autonomous flight. The SSEF is an end-to-end tool composed of several modular blocks which model the wing aerodynamics and dynamics, the body dynamics, and in the future, the environment perception, control algorithms, the actuators dynamics, and the visual and inertial sensors. We present the current state of the art of its implementation, and preliminary results.

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Karasu, İlyas, Mustafa Özden, and Mustafa Serdar Genç. "Performance Assessment of Transition Models for Three-Dimensional Flow Over NACA4412 Wings at Low Reynolds Numbers." Journal of Fluids Engineering 140, no. 12 (June 13, 2018). http://dx.doi.org/10.1115/1.4040228.

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The performance of the transition models on three-dimensional (3D) flow of wings with aspect ratios (AR) of 1 and 3 at low Reynolds number was assessed in this study. For experimental work; force measurements, surface oil and smoke-wire flow visualizations were performed over the wings with NACA4412 section at Reynolds numbers of 2.5 × 104, 5 × 104, and 7.5 × 104 and the angles of attack of 8 deg, 12 deg, and 20 deg. Results showed that the AR had significant effects on the 3D flow structure over the wing. According to the experimental and numerical results, the flow over the wing having lower ARs can be defined with wingtip vortices, axial flow, and secondary flow including spiral vortex inside the separated flow. When the angle of attack and Reynolds number was increased, wing-tip vortices were enlarged and interacted with the axial flow. At higher AR, flow separation was dominant, whereas wing-tip vortices suppressed the flow separation over the wing with lower AR. In the numerical results, while there were some inconsistencies in the prediction of lift coefficients, the predictions of drag coefficients for two transition models were noticeably better. The performance of the transition models judged from surface patterns was good, but the k–kL–ω was preferable. Secondary flow including spiral vortices near the surface was predicted accurately by the k–kL–ω. Consequently, in comparison with experiments, the predictions of the k–kL–ω were better than those of the shear stress transport (SST) transition.

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Lu, A., and T. Lee. "Effect of Ground Boundary Condition on Near-Field Wingtip Vortex Flow and Lift-Induced Drag." Journal of Fluids Engineering 143, no. 3 (November 18, 2020). http://dx.doi.org/10.1115/1.4048875.

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Abstract The ground proximity is known to induce an outboard movement and suppression of the wingtip vortices, leading to a reduced lift-induced drag. Depending on the ground boundary condition, a large scatter exists in the published lift-induced drag and vortex trajectory. In this experiment, the ground boundary condition-produced disparity in the vortex strength and induced drag were evaluated. No significant discrepancy appeared for a ground distance or clearance larger than 30% chord. As the stationary ground was further approached, there was the appearance of a corotating ground vortex (GV), originated from the downstream progression of a spanwise ground vortex filament, which added vorticity to the tip vortex, leading to a stronger tip vortex and a larger lift-induced drag compared to the moving ground. For the moving ground, the ground vortex was absent. In close ground proximity, the rollup of the high-pressure fluid flow escaped from the wing's tip always caused the formation of a counter-rotating secondary vortex, which dramatically weakened the tip vortex strength and produced a large induced-drag reduction. The moving ground effect, however, induced a stronger secondary vortex, leading to a smaller lift-induced drag and a larger outboard movement of the tip vortex as compared to the stationary ground effect.

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Lee, T. "Impact of Gurney Flaplike Strips on the Aerodynamic and Vortex Flow Characteristic of a Reverse Delta Wing." Journal of Fluids Engineering 138, no. 6 (February 18, 2016). http://dx.doi.org/10.1115/1.4032301.

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The impact of Gurney flaplike strips, of different geometric configurations and heights, on the aerodynamic characteristics and the tip vortices generated by a reverse delta wing (RDW) was investigated via force-balance measurement and particle image velocimetry (PIV). The addition of side-edge strips (SESs) caused a leftward shift of the lift curve, resembling a conventional trailing-edge flap. The large lift increment overwhelmed the corresponding drag increase, thereby leading to an improved lift-to-drag ratio compared to the baseline wing. The lift and drag coefficients were also found to increase with the strip height. The SES-equipped wing also produced a strengthened vortex compared to its baseline wing counterpart. The leading-edge strips (LESs) were, however, found to persistently produce a greatly diffused vortex flow as well as a small-than-baseline-wing lift in the prestall α regime. The downward LES delivered a delayed stall and an increased maximum lift coefficient compared to the baseline wing. The LESs provide a potential wingtip vortex control alternative, while the SESs can enhance the aerodynamic performance of the RDW.

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Moskalenko, V. O., A. V. Tsoy, and A. A. Nedogarok. "The study of aerodynamic characteristics of the wing with tips of different shapes." Engineering Journal: Science and Innovation, no. 10 (94) (October 2019). http://dx.doi.org/10.18698/2308-6033-2019-10-1921.

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Winglets or wingtips of various types are a common means of improving fuel efficiency of a modern aircraft. Aircraft manufacturers and research teams are actively searching for new types of winglets. The purpose of this work is to compare the efficiency of a number of used and promising end superstructures of different shapes. The paper presents the results of a numerical experiment to assess the effect of the four types of wingtips on the isolated wing aerodynamic characteristics. The increase in aerodynamic quality and the change in the inductive resistance of the wing, as well as the intensity of the end vortices, are compared. Validation of the numerical calculation and analysis of the results are performed. The article can be used as a base material for further research of methods for reducing inductive resistance and improving the efficiency of aircraft of different configurations.

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Journal articles on the topic 'Wingtip Vortices'

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