Evolution of vortical structures in the shear-layer of delta wings

Washburn, Anthony E.; Visser, Kenneth D.

doi:10.2514/6.1994-2317

Cited by 31 publications

(17 citation statements)

References 2 publications

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“…They include Squire et al, 10 Gad-el-Hak and Blackwelder, 11,12 Payne et al, 13 Lowson, 14 and Reynolds and Abtahi. 15 Further, time-averaged quantitative characterizations of vortical substructures involve the work of Verhaagen et al, 16 Washburn and Visser, 17 Lowson et al, 18 Riley and Lowson, 19 and Mitchell et al 20 The occurrence of vortical substructures was first computed by Gordnier and Visbal 21,22 who demonstrated their existence in the absence of external forcing. Mitchell et al 23 and Mitchell and Molton 24 also have computed patterns of vortical substructures using a different numerical approach.…”

Section: B Flow Structure On Highly Swept Wingsmentioning

confidence: 99%

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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Section: B Flow Structure On Highly Swept Wingsmentioning

confidence: 99%

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

Yanıktepe

Rockwell

2005

AIAA Journal

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“…It is interesting to note that the substructures follow a helical trajectory around the vortex core and the spacing (frequency) between the substructures appears relatively constant, confirming the observations of Washburn and Visser. 17 Additionally, the substructures remain coherent even in the post-breakdown region of the flowfield. There are some discontinuities in the results presented in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…secondary vortices. 10 ,20 Washburn and Visser 17 suggested the substructures are generated by nonviscous instabilities in the shear layer and that their formation is governed by the transverse flow of the leading-edge vortices. Yet another hypothesis postulates that a longitudinal instability associated with the curvature of the separating shear layer is at the origin of the substructures.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Delta-Wing Vortical Substructures Using Detached-Eddy Simulation

et al. 2006

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An u nderstanding of the vortical structures which comprise the vortical flowfield around slender bodies is essential for the development of highly maneuverable and high angle of attack flight. This is primarily due to the physical limits these phenomena impose on aircraft and missile s at extreme flight conditions. D emands for more maneuverable air vehicles have pushed the limits of current CFD methods in the high Reynolds number regime. Simulation methods must be able to accurately describe the unsteady, vortic al flowfields associated with fighter aircraft at Reynolds numbers more representative of full scale vehicles. It is the goal of this paper to demonstrate the ability of DetachedEddy Simulation, a hybrid RANS-LES method, to accurately model the vortical flowfield over a slender delta wing at Reynolds numbers above 1 million. Detached-Eddy Simulation has successfully predicted the location of the vortex breakdown phenomenon and the goal of the current effort is to analyze and assess the influence of vortical substructures in the separating shear layers which roll up to form the leading-edge vortices. Very detailed experiments performed at O NERA using 3 -D Laser Doppler Velocimetry measurement will be used to compare simulations utilizing DES turbulence models. The computational results provide novel insight into the formation and impact of the vortical substructures in the separating shear layers on the entire vortical flowfield.

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“…Once it is initiated, this interaction process no longer requires external perturbations to sustain it. At present, the exact triggering source for our experiments is not clear, although we suspect that inherent disturbances from the experimental setup (the vibration of the water towing tank facility) might be responsible, as another study 15 has suggested. Hubner and Komerath 16 have studied the quasi-periodic velocity uctuations over a delta wing and showed the existence of uctuating energy within a narrow frequency bandwidth.…”

Section: Reconnection Of the Primary Vortex And The Shear Layermentioning

confidence: 94%

Numerical Study of N-Wave Propagation Using Optimized Compact Finite Difference Schemes

2003

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primary vortex.As expected,increase/decreaseof the feedingrate of the shear-layer vorticity leads directly to the enhancing/weakening of the primary vortex, respectively. Vorticity from the secondary vortexcan be carriedinto the primary vortex as indicatedby the presence of low-level counterclockwise vorticity in the primary vortex in the original PIV data. However, the entrained counterclockwise vorticity is relatively weak compared to the primary vorticity so it has not shown up in the interpolated vorticity data. Nevertheless, it can still play a role in weakening the primary vortex as suggested by Gordnier and Visbal 14 in their computational work. Weakening of Both the Primary and the Secondary VorticesThe secondary vortex is signi cantly weakened after part of its vorticity is ejected from the surface. On the other hand, the weakening of the primary vortex results in the weakening of outboard-moving boundary-layer ow and this consequently hinders the recoveryof the secondaryvortex. In other words, one would expect that the feeding of vorticity into the secondary vortex would be related to the instantaneous variation of the total circulation of the primary vortex. Time variations of the circulation of the primary vortex and the vorticity ux of the secondary vortex are found to be strongly correlated (not shown here). Reconnection of the Primary Vortex and the Shear LayerThe weakening of the primary vortex implies a smaller induction force on the secondary vortex. As a result, the secondary vortex settles back to the surface. In addition,the secondary vortex reduces in size and strength because of its ejection. The reduced in uence of the secondary vortex allows the reconnection of the shear layer with the primary vortex, which in turn resumes the feeding of the shear-layer vorticity into the primary vortex. This event reenergizes the primary vortex, and a new cycle of the primary/secondaryvortex interaction repeats.It is clear from the preceding discussions that the primary/ secondary vortex interaction process assumes a self-sustainedmanner. Once it is initiated, this interaction process no longer requires external perturbations to sustain it. At present, the exact triggering source for our experiments is not clear, although we suspect that inherent disturbances from the experimental setup (the vibration of the water towing tank facility) might be responsible, as another study 15 has suggested. Hubner and Komerath 16 have studied the quasi-periodic velocity uctuations over a delta wing and showed the existence of uctuating energy within a narrow frequency bandwidth. They further showed that the quasi-periodicity originated in the outboard region along the leading edge of the wing. This is consistent with the current observation that the interaction between the primary vortex and the secondary vortex occurs outboard near the leading edge.Even in the absence of any inherent disturbancesfrom the experimental setup, such ejection phenomenon has been observed in a numerical study. 5 Because the interaction is es...

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Evolution of vortical structures in the shear-layer of delta wings

Cited by 31 publications

References 2 publications

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

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

Analysis of Delta-Wing Vortical Substructures Using Detached-Eddy Simulation

Numerical Study of N-Wave Propagation Using Optimized Compact Finite Difference Schemes

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