CEAS Aeronautical Journal

, Volume 5, Issue 2, pp 109–125

Enhancement of aircraft wake vortex decay in ground proximity

Experiment versus Simulation

Authors

    • Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
  • Frank Holzäpfel
    • Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
  • Takashi Misaka
    • Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
  • Reinhard Geisler
    • Institut für Aerodynamik und Strömungstechnik, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
  • Robert Konrath
    • Institut für Aerodynamik und Strömungstechnik, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Original Paper

DOI: 10.1007/s13272-013-0094-8

Cite this article as:
Stephan, A., Holzäpfel, F., Misaka, T. et al. CEAS Aeronaut J (2014) 5: 109. doi:10.1007/s13272-013-0094-8

Abstract

Aircraft wake vortex evolution in ground proximity is investigated experimentally in a water towing tank, as well as numerically with wall-resolved large eddy simulation (LES). With these complementary instruments the enhancement of wake vortex decay by obstacles, introduced at the ground surface, is analyzed. The experimental methods include time-resolved stereo particle image velocimetry and vortex core visualization. For comparison with the experiment, the LES considers the turbulent wake of the strut, holding the towed aircraft model. Wake vortex trajectories and circulation decay are compared at different distances from the obstacle. Tracers are employed to visualize the obstacle’s effects on the vortex core, in LES and experiment. The experimentally obtained trajectories and decay characteristics are reproduced qualitatively by simulations, whereas the agreement is degraded at later times. Beyond that, the vortex dynamics, deduced from the LES results, help to understand the experimental observations. The obstacles trigger helical secondary vortex structures, propagating along the primary vortices. The observed propagation speed of the helical disturbance is fairly well predicted by the suggested simple model. It is shown that the obstacles significantly modify the vortex interaction with the ground and substantially accelerate vortex decay. Two neighboring obstacles lead to colliding disturbances that further enhance vortex decay rates.

Keywords

Wake vortex flow Ground effect Decay enhancement Large eddy simulation Towing tank Particle image velocimetry Obstacles

List of symbols

Symbols

\(\varGamma\)

Circulation, m2/s

\(\varGamma_0\)

Initial vortex circulation, m2/s

\(\nu\)

Molecular viscosity, m2/s

\(\nu_{\rm t}\)

Turbulent viscosity, m2/s

ω

Vorticity, 1/s

ω x ω y ω z

Vorticity components, 1/s

ρ

Density, kg/m3

σ

Standard deviation

a

Radius of secondary vortex structure, m

AB

Parameters for strut wake turbulence model

b 0

Initial vortex separation, m

C

Chord length, mm

C D

Drag coefficient, 1/m

d

Chord thickness, mm

E strut

Turbulent kinetic energy of strut wake, Nm

\(E_\varGamma\)

Turbulent kinetic energy of the vortex, Nm

h 0

Initial vortex height, m

L x L y L z

Dimensions, m

l strut

Length of the strut, m

N x N y N z

Grid points

p

Pressure, N/m2

R

Curvature radius, m

\(Re_\varGamma\)

Vortex Reynolds number

\(Re_{\rm c}\)

Chord Reynolds number based on towing speed

r c

Vortex core radius, m

t

Time, s

t 0

Time unit, s

U 0

Towing speed, m/s

u i uvw

Velocity components, m/s

U hel

Propagation speed of helix front, m/s

V 0

Initial vortex descent speed, m/s

x i xyz

Coordinates, m

\(\Updelta x\)

Distance to obstacle, m

Subscripts

0

Reference state

max

Maximum value

rms

Root mean square

hel

Helix

L

LES

ring

Ring

W

WSG

Superscripts

Deviation from reference state

*

Normalized with respect to vortex flow

+

Normalized by chord length

Abbreviations

DLR

German Aerospace Center

ICAO

International Civil Aviation Organization

LES

Large-eddy simulation

PIV

Particle image velocimetry

SVS

Secondary vortex structure

WSG

Wasser Schleppkanal Göttingen

WVAS

Wake vortex advisory system

Copyright information

© Deutsches Zentrum für Luft- und Raumfahrt e.V. 2013