Wake Vortex Behaviour in the Sheared Boundary Layer

last modified April 2002, Thomas Hofbauer

CONTENT

Vortex Decay in Constant shear ; [gif-version] [mpg-version]
Aircraft Wake Vortices - The Heathrow-Rebound Case  [link]
Shear-Layer Effects on the Dynamics of a Counter-Rotating Vortex Pair  [link]
Effects of nonlinear Shear on the Dynamics of a Counter-Rotating Vortex Pair  [link]



Aircraft Wake Vortices
The Heathrow-Rebound Case

published in: Holzäpfel, F., Hofbauer, T., Gerz, T., Schumann, U. (2002):
Aircraft Wake Vortex Evolution and Decay in Idealized and Real Environments: Methodologies, Benefits and Limitations, Fluid Mechanics and its Applications, Vol. 65, Advances in LES of Complex Flows, edited by R. Friedrich, W. Rodi, Kluwer Academic Publishers, Dordrecht,  ISBN 1-4020-0486-9, pp. 293-309.
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Selected Figures
Reconstruction of vortex trajectories from measured LDV data of a Boeing B747-200 in terminal approach.
Isolines/isosurfaces of lambda_2 (measure for coherent vortex structures) at t=19s after vortex injection of a preliminary DNS. At this stage, the upwind vortex almost reached its lowest altitude and is just about to reverse its lateral movement direction, forming the characteristic loop of the trajectory.


Animation mpeg version (2 MB)

 
Shear-Layer Effects on the Dynamics of a
Counter-Rotating Vortex Pair

Thomas Hofbauer & Thomas Gerz

AIAA Paper 2000-0758
38th AIAA Aerospace Sciences Meeting and Exhibit, 2000/Reno, NV

Abstract
The influence of three-dimensional wind-shear layers (jets) on the transport and decay of a counter-rotating vortex pair is investigated by means of direct numerical simulation. A laminar case is considered where the jet width varies periodically along the vortex axis. Further, the impact of two turbulence levels in the jet upon the vortex pair is studied. The initially laminar vortex pair penetrates from above into the jet and towards the ground. When penetrating into the laminar jet the wake vortices experience a sinusoidal perturbation but do not link.  Contrarily, mutually independent dissolution of each vortex is observed when the jet is turbulent. The upstream vortex with vorticity opposing the vorticity of the upper shear layer of the jet starts to erode when it touches the upper flank of the turbulent jet, whereas the downstream vortex remains unaffected until it interacts with the lower shear layer below the jet maximum. The vortex breakdown process and its spatial structure is discussed in detail.  

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Animation
Interaction of wake vortices with a turbulent low-level jet

animated gif version (2 MB)
mpeg version (0.2 MB)
Selected figures
(Click on Thumbnail to get a larger view)

Dynamic pressure deviation p'c at the center of the upstream vortex vs. axial coordinate. The values are an average over 3x3 cells surrounding the local minimum of lambda2.

see full paper for more details.


Time series of circulation obtained at 3 times the core radius and averaged over axial direction.

see full paper for more details.


Azimuthal structures and short-wave perturbations in case T0. Isosurfaces of azimuthal vorticity (dark) and +6.9 (light) and of lambda2=-77.6 with respect to upwind vortex location.

see full paper for more details.



 


Effects of nonlinear Shear on the Dynamics of a
Counter-Rotating Vortex Pair

Thomas Hofbauer & Thomas Gerz

Proceedings for the 1st Int'l Symposium on
Turbulence and Shear Flow Phenomena, 1999, Santa Barbara

Abstract
Numerical simulations were conducted to investigate the influence of nonlinear vertical shear on the trajectories of a trailing vortex pair. Descending vortices which approach a shear layer begin to tilt and diverge. It is shown that the vortex whose vorticity is of opposite sign to the shear-layer vorticity can stall or even rebound, whereas the other vortex penetrates through the shear layer. The behaviour of the vortices is highly sensitive to the vorticity distribution within the shear layer and cannot be described by circulation or maximum vorticity relations. When the vorticity distribution of the shear layer varies along the axis of the vortices, the interaction between shear and vortex is also modified in axial direction and presumably triggers a quickly growing instability of the vortex pair.

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Selected figures
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