Vortex flows over fixed-wing micro air vehicles

Gursul, Ismet; Taylor, Gordon; Wooding, C L

doi:10.2514/6.2002-698

Cited by 40 publications

(16 citation statements)

References 16 publications

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“…For the low-aspect-ratio (AR) wing, they found that the lift became increasing nonlinear as aspect ratio was less than 1. Compared to the high-Reynolds-number wings, the presence of strengthening wing-tip vortices with decreasing wing AR had similar effects on the lift-curve slope (decreased) and the maximum lift coefficient and corresponding angle of attack (increased) [13]. These AR-related trends are similar to high-Reynolds-number wings, an effect of the bound vorticity.…”

mentioning

confidence: 76%

Geometry and Prestrain Effects on the Aerodynamic Characteristics of Batten-Reinforced Membrane Wings

Zheng

Martin

Wrist

et al. 2016

Journal of Aircraft

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To lessen the deterioration of fixed-wing aerodynamic performance associated with chord Reynolds numbers below 100,000, flexible membrane wing designs have been studied and proposed as an alternative for micro air vehicle use. The beneficial effects of a flexible membrane can include higher lift, steeper lift-curve slope, delayed stall, gentle stall characteristics, and greater efficiency. These benefits have been attributed to both the time-averaged and dynamic deformation of the membrane. This work discusses the geometric and prestrain effects on a battenreinforced, free trailing-edge membrane wing in low-Reynolds-number (50,000) flow. The global aerodynamic forces on the wings with varying wing aspect ratio, cell aspect ratio, and prestrain level were measured. The results show that the aerodynamic advantages of the flexible membrane are retained for the low-aspect-ratio wings. The optimal membrane cell aspect ratio is found to be approximately 1. The comparison of the aerodynamic forces between the low-aspect-ratio membrane wings and the corresponding three-dimensional-printed wings with the time-averaged deformation indicates the importance of membrane dynamic motion for the derived aerodynamic benefits.

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mentioning

confidence: 76%

Geometry and Prestrain Effects on the Aerodynamic Characteristics of Batten-Reinforced Membrane Wings

Zheng

Martin

Wrist

et al. 2016

Journal of Aircraft

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“…Gursul et al 25 summarized recent investigations of low-aspectratio wings and planforms and, furthermore, provide insight into the phenomena of vortex breakdown visualized by dye injection. The consequences of low sweep angle were clearly evident.…”

Section: Flow Structure On Ucav Planformsmentioning

confidence: 98%

Flow Structure on Diamond and Lambda Planforms: Trailing-Edge Region

Yanıktepe

Rockwell

2005

AIAA Journal

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The instantaneous and averaged flow structure on diamond and lambda planforms is characterized by using a technique of high-image-density particle image velocimetry. Emphasis is on the structure in the trailing-edge region, over a range of angle of attack. Elongated layers of vorticity in the crossflow plane exhibit well-defined mean (time-averaged) and instantaneous concentrations of vorticity. These features are interpreted in conjunction with patterns of streamline topology, as well as images of rms velocity fluctuation and velocity spectra obtained from space-time imaging. NomenclatureC = root chord of entire planform, mm C = root chord of leading (delta-wing) portion of planform, mm f = frequency, Hz S = local semispan of wing, mm S w = spectrum of w component of velocity fluctuation U = freestream velocity, mm/s V = magnitude of velocity vector, mm/s v = instantaneous velocity fluctuation in direction parallel to surface of wing, mm/s w = instantaneous velocity fluctuation normal to surface of wing, mm/s w rms = rms of velocity fluctuation, mm/s x = distance from apex measured along plane of symmetry of wing, mm y = distance measured normal to plane of symmetry of wing, mm α = angle of attack, deg = sweep angle, deg ψ = stream function, mm 2 /s ω = vorticity, 1/s = time-averaged value of quantity

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“…At these very low Reynolds numbers, vortices exhibit wake-like axial velocity profiles even upstream of breakdown [11,12,13]. The vortices form close to the surface of the wing [14], and vortex/boundary layer interaction becomes important [15,16]. A further consequence of the interaction between the boundary layer and vortex flows is the sensitivity of non-slender wing flows to the Reynolds number that is not observed over slender wings [17].…”

Section: Overviewmentioning

confidence: 99%

Unsteady aerodynamics of nonslender delta wings

Gursul

Gordnier

Visbal

2005

Progress in Aerospace Sciences

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273

138

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Unsteady aerodynamics of nonslender delta wings, covering topics of shear layer instabilities, structure of nonslender vortices, breakdown, maneuvering wings, and fluid/structure interactions, are reviewed in this paper. Vortical flows develop at very low angles of attack, and form close to the wing surface. This results in strong interactions with the upper-surface boundary layer and in a pronounced dependence of the flow structure on Reynolds number. Vortex breakdown is observed to be much less abrupt compared to breakdown over slender wings. This results in challenges for the precise determination of vortex breakdown location and the interpretation of flow visualizations. One of the distinct features of nonslender wings is the location of the primary attachment zone outboard of the symmetry plane. Reattachment location correlates with the wing stall process and increased buffeting. Dramatic fluid/structure interactions emerge with increasing wing flexibility and result in substantial lift enhancement in the post-stall region. This recently discovered phenomenon appears to be a feature of nonslender wings. Rigid delta wings undergoing small amplitude oscillations in the post-stall region exhibit many similarities to flexible wings, including reattachment and reformation of the leading-edge vortices. Unusual self-excited roll oscillations have also been observed for free-to-roll nonslender wings.

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Vortex flows over fixed-wing micro air vehicles

Cited by 40 publications

References 16 publications

Geometry and Prestrain Effects on the Aerodynamic Characteristics of Batten-Reinforced Membrane Wings

Geometry and Prestrain Effects on the Aerodynamic Characteristics of Batten-Reinforced Membrane Wings

Flow Structure on Diamond and Lambda Planforms: Trailing-Edge Region

Unsteady aerodynamics of nonslender delta wings

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