The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Ignazio Maria Viola - One of the best experts on this subject based on the ideXlab platform.
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The Leading-Edge Vortex of yacht sails
Ocean Engineering, 2018Co-Authors: Abel Arredondo-galeana, Ignazio Maria ViolaAbstract:Abstract It has been suggested that a stable Leading Edge Vortex (LEV) can be formed from the sharp Leading Edge of asymmetric spinnakers, which are high-lift sails used by yachts to sail downwind. If the LEV remains stably attached to the Leading Edge, it provides an increase in the thrust force. Until now, however, the existence of a stable and attached LEV has only been shown by numerical simulations. In the present work we experimentally verify, for the first time, that a stable LEV can be formed on an asymmetric spinnaker. We tested a 3D printed rigid sail in a water flume at a chord-based Reynolds number of ca. 10 4 . The sail was tested in isolation without hull and rigging. The flow field was measured with Particle Image Velocimetry (PIV) over horizontal cross sections. We found that on the leeward side of the sail (the suction side), the flow separates at the Leading Edge reattaching further downstream and forming a stable LEV. The LEV grows in diameter from the root to the tip of the sail, where it merges with the tip Vortex. We detected the LEV using the γ criterion, and we verified its stability over time. The lift contribution provided by the LEV was computed solving a complex potential model of each sail section. This analysis indicated that the LEV provides more than 20% of the total sail's lift. These findings suggest that the maximum lift of low-aspect-ratio wings with a sharp Leading Edge, such as spinnakers, can be enhanced by promoting the formation of a stable LEV.
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The Leading-Edge Vortex of swift wing-shaped delta wings
Royal Society open science, 2017Co-Authors: Rowan Muir, Abel Arredondo-galeana, Ignazio Maria ViolaAbstract:Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the Leading-Edge Vortex (LEV) for lift generation in a variety of flight conditions. A well-documented example of an LEV is that generated by aircraft with highly swept, delta-shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowlEdge can serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, a model non-slender delta-shaped wing with a sharp Leading Edge is tested at low Reynolds number, along with a delta wing of the same design, but with a modified trailing Edge inspired by the wing of a common swift Apus apus. The effect of the tapering swift wing on LEV development and stability is compared with the flow structure over the unmodified delta wing model through particle image velocimetry. For the first time, a Leading-Edge Vortex system consisting of a dual or triple LEV is recorded on a swift wing-shaped delta wing, where such a system is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the trailing-Edge geometry of the swift wing alone does not prevent the common swift from generating an LEV system comparable with that of a delta-shaped wing.
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The Leading-Edge Vortex of swift wings
2017Co-Authors: Ignazio Maria Viola, Rowan MuirAbstract:Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the Leading-Edge Vortex (LEV) for lift generation in a variety of flight conditions. A well documented example of an LEV is that generated by aircraft with highly swept, delta shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowlEdge will serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, the wing of a common swift Apus apus is simplified to a model with swept wings and a sharp Leading-Edge, making it readily comparable to a model delta shaped wing of the same Leading-Edge geometry. Particle image velocimetry provides an understanding of the effect of the tapering swift wing on LEV development and stability, compared with the delta wing model. For the first time a dual LEV is recorded on a swift shaped wing, where it is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the common swift is able to generate a dual LEV while gliding, potentially delaying Vortex breakdown by exploiting other features non explored here, such as wing twist and flexibility. It is further suggested that the Vortex system could be used to damp loading fluctuations, reducing energy expenditure, rather than for lift augmentation.
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Leading Edge Vortex dynamics
2015Co-Authors: Richards Peter J, Ignazio Maria ViolaAbstract:Leading Edge vortices can create high local pressures which in some situations may be advantageous but in others may cause damage. This paper looks at three wind engineering situations: windborne debris, roof suctions on a low-rise building and pressures near the luff of a downwind sail, where the behaviour of the Leading Edge Vortex is significant. In some of these situations the strength of the Vortex varies in a random and intermittent manner while in others the process is directly linked to the motion of the structure.
James Buchholz - One of the best experts on this subject based on the ideXlab platform.
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Vorticity transport and the Leading-Edge Vortex of a plunging airfoil
Experiments in Fluids, 2015Co-Authors: Azar Eslam Panah, James Akkala, James BuchholzAbstract:The three-dimensional flow field was experimentally characterized for a nominally two-dimensional flat-plate airfoil plunging at large amplitude and reduced frequencies, using three-dimensional reconstructions of planar PIV data at a chord-based Reynolds number of 10,000. Time-resolved, instantaneous PIV measurements reveal that secondary vorticity, of opposite sign to the primary Vortex, is intermittently entrained into the Leading-Edge Vortex (LEV) throughout the downstroke, with the rate of entrainment increasing toward the end of the stroke when the Leading-Edge shear layer weakens. A planar vorticity transport analysis around the LEV indicated that, during the downstroke, the surface vorticity flux due to the pressure gradient is consistently about half that due to the Leading-Edge shear layer for all parameter values investigated, demonstrating that production and entrainment of secondary vorticity is an important mechanism regulating LEV strength. A small but non-negligible vorticity source was also attributed to spanwise flow toward the end of the downstroke. Aggregate Vortex tilting is notably more significant for higher plunge frequencies, suggesting that the Vortex core is more three-dimensional.
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vorticity transport in the Leading Edge Vortex on a rotating blade
Journal of Fluid Mechanics, 2014Co-Authors: Craig Wojcik, James BuchholzAbstract:Vorticity transport is analysed within the Leading-Edge Vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the Leading-Edge Vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the Leading-Edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the Leading-Edge Vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of Leading-Edge-Vortex circulation. Thus, it provides an important condition for maintenance of an attached Leading-Edge Vortex on the inboard portion of the blade.
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Parameter Variation and the Leading-Edge Vortex of a Rotating Flat Plate
AIAA Journal, 2014Co-Authors: Craig Wojcik, James BuchholzAbstract:Particle image velocimetry was used to characterize the flowfield on flat plates of aspect ratios 2 and 4 undergoing a starting rotation motion at Reynolds numbers, based on tip velocity, of 4,000, 8,000, and 16,000. The starting motion was performed in a tank of quiescent water. For both aspect ratios, a Leading-Edge Vortex was observed on the suction surface of the plate, and its evolution and circulation were characterized with variations in angle of attack, Reynolds number, and azimuthal and spanwise positions. A region of strong counter-rotating vorticity was also observed between the Leading-Edge Vortex and the plate surface, which becomes entrained by the Leading-Edge Vortex. The circulation of the Leading-Edge Vortex, when rendered dimensionless by the plate chord length and tip speed, was found to be relatively insensitive to Reynolds number and the azimuthal position of the plate within the ranges of the measurements; however, a strong (approximately linear) dependence on angle of attack was obs...
Rowan Muir - One of the best experts on this subject based on the ideXlab platform.
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The Leading-Edge Vortex of swift wing-shaped delta wings
Royal Society open science, 2017Co-Authors: Rowan Muir, Abel Arredondo-galeana, Ignazio Maria ViolaAbstract:Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the Leading-Edge Vortex (LEV) for lift generation in a variety of flight conditions. A well-documented example of an LEV is that generated by aircraft with highly swept, delta-shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowlEdge can serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, a model non-slender delta-shaped wing with a sharp Leading Edge is tested at low Reynolds number, along with a delta wing of the same design, but with a modified trailing Edge inspired by the wing of a common swift Apus apus. The effect of the tapering swift wing on LEV development and stability is compared with the flow structure over the unmodified delta wing model through particle image velocimetry. For the first time, a Leading-Edge Vortex system consisting of a dual or triple LEV is recorded on a swift wing-shaped delta wing, where such a system is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the trailing-Edge geometry of the swift wing alone does not prevent the common swift from generating an LEV system comparable with that of a delta-shaped wing.
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The Leading-Edge Vortex of swift wings
2017Co-Authors: Ignazio Maria Viola, Rowan MuirAbstract:Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the Leading-Edge Vortex (LEV) for lift generation in a variety of flight conditions. A well documented example of an LEV is that generated by aircraft with highly swept, delta shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowlEdge will serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, the wing of a common swift Apus apus is simplified to a model with swept wings and a sharp Leading-Edge, making it readily comparable to a model delta shaped wing of the same Leading-Edge geometry. Particle image velocimetry provides an understanding of the effect of the tapering swift wing on LEV development and stability, compared with the delta wing model. For the first time a dual LEV is recorded on a swift shaped wing, where it is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the common swift is able to generate a dual LEV while gliding, potentially delaying Vortex breakdown by exploiting other features non explored here, such as wing twist and flexibility. It is further suggested that the Vortex system could be used to damp loading fluctuations, reducing energy expenditure, rather than for lift augmentation.
Kenichi Rinoie - One of the best experts on this subject based on the ideXlab platform.
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estimation of take off performance for supersonic transport with Leading Edge Vortex flaps and trailing Edge flaps
Journal of The Japan Society for Aeronautical and Space Sciences, 2003Co-Authors: Katsuhiro Miyata, Kenichi RinoieAbstract:Improvements of the take-off and climb performance of the next generation supersonic transport (SST) are one of the key features for the SST development. Take-off and climb performances have been estimated for the cranked-arrow-wing SST configuration when the Leading-Edge Vortex flaps and the trailing-Edge flaps are deflected. Results show that the take-off distance and the balanced field length are reduced when the trailing-Edge flaps are deflected, as expected. The thrust required for the constant climb gradient can be reduced when the Leading-Edge Vortex flaps and the trailing-Edge flaps are deflected at the same time.
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Leading Edge Vortex flaps for supersonic transport configuration effects of flap configurations and rounded Leading Edges
2002Co-Authors: Kenichi Rinoie, Dong Youn Kwak, Katsuhiro Miyata, Masayoshi NoguchiAbstract:Wind tunnel measurements were done on a cranked arrow wing SST configuration with Leading-Edge Vortex flaps. Force and surface pressure measurements were made at the Reynolds number based on the wing mean aerodynamic chord of 9.2x10 5 to 3.8x10 6 . Two different flap cross sections (the originally designed “non-rounded” Leading-Edge and the rounded Leading-Edge) were tested. The purpose of the measurements is to clarify how the differences of the Reynolds number affect the flow around the rounded Leading-Edge Vortex flaps and the flap performance. The wing with the rounded Leading-Edge Vortex flaps indicated some benefit of the lift/drag ratio as compared with those of the “non-rounded” Vortex flaps at a relatively high lift coefficient greater than 0.3. Different flow patterns were observed over the rounded Leading-Edge Vortex flaps when the Reynolds number is increased at a lift coefficient greater than 0.5. The spanwise length of the separated region shortens as the Reynolds number is increased. However, this flow pattern change has only a little influence on the wing lift/drag ratio itself in the range of the tested Reynolds numbers.
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Experiments on a 60-Degree Delta Wing with Rounded Leading-Edge Vortex Flaps
Journal of Aircraft, 2000Co-Authors: Kenichi RinoieAbstract:Low-speed wind-tunnel measurements were done on a 1.15-m span 60-deg delta wing with rounded Leading-Edge Vortex flaps. The purpose of the measurements is to assess the benefits of the rounded Leading-Edge Vortex flaps in regard to improving the lift/drag ratio of delta wings. Force and surface pressure measurements were made at a Reynolds number based on a centerline chord of 2 x 10 6 . The increase in the radius of the rounded Leading Edge reduces the drag significantly both with and without flap deflection except in the minimum drag region. Deflecting the rounded Leading-Edge Vortex flap improves the lift/drag ratio at relatively higher lift coefficients, when compared with the sharp-Edged Vortex flap. The largest improvement in the lift/drag ratio as compared with the sharp-Edged delta wing with Vortex flaps is more than 25% in the lift coefficient range between about 0.6 and 0.8 for the rounded-Edge delta wing with flaps that were deflected 30 deg downward
Craig Wojcik - One of the best experts on this subject based on the ideXlab platform.
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vorticity transport in the Leading Edge Vortex on a rotating blade
Journal of Fluid Mechanics, 2014Co-Authors: Craig Wojcik, James BuchholzAbstract:Vorticity transport is analysed within the Leading-Edge Vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the Leading-Edge Vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the Leading-Edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the Leading-Edge Vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of Leading-Edge-Vortex circulation. Thus, it provides an important condition for maintenance of an attached Leading-Edge Vortex on the inboard portion of the blade.
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Parameter Variation and the Leading-Edge Vortex of a Rotating Flat Plate
AIAA Journal, 2014Co-Authors: Craig Wojcik, James BuchholzAbstract:Particle image velocimetry was used to characterize the flowfield on flat plates of aspect ratios 2 and 4 undergoing a starting rotation motion at Reynolds numbers, based on tip velocity, of 4,000, 8,000, and 16,000. The starting motion was performed in a tank of quiescent water. For both aspect ratios, a Leading-Edge Vortex was observed on the suction surface of the plate, and its evolution and circulation were characterized with variations in angle of attack, Reynolds number, and azimuthal and spanwise positions. A region of strong counter-rotating vorticity was also observed between the Leading-Edge Vortex and the plate surface, which becomes entrained by the Leading-Edge Vortex. The circulation of the Leading-Edge Vortex, when rendered dimensionless by the plate chord length and tip speed, was found to be relatively insensitive to Reynolds number and the azimuthal position of the plate within the ranges of the measurements; however, a strong (approximately linear) dependence on angle of attack was obs...