Aerodynamic Ground Effect: a case-study of the integration of CFD and experiments
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Aerodynamic Ground Effect: a case-study of the integration
of CFD and experiments
Tracie Barber & Stephen HallUniversity of New South Wales,
Sydney, Australia
Introduction
• Ground Effect
• Issues causing discrepancies in results
• Boundary Conditions– Deformable surface
• Viscous Effects
• Moving Ground design and analysis
• Continuing work
Ground effect - applications
WIG400
0
-400
-800
-1000
40
20
0
kPa m/s
Pressure Velocity
Previous Research
• Inviscid (ie panel methods) used extensively
• Analytical methods also used (many assumptions, limitations)
• Limited viscous CFD results• Inappropriate boundary conditions often
used• Experimental results scarce / unreliable
Current Work
• Reynolds-Averaged Navier Stokes Equations (CFX & Fluent)
• Higher order discretising schemes
• RNG or Realizable k- turbulence model, standard wall functions
Test-cases
Testcases: (2D)
• NACA 4412 wing
• Angles of attack:– 1.2O, 4O, 6.4O, 10O, 12O
• Reynolds Number:– 8,200,000
• Clearances (h/c):– 0.05, 0.10, 0.50, 1.00, free air
Boundary conditions
IMAGE SLIP
GROUND STATIONARY GROUND MOVING
u=Uu=U
Results - velocity vectorsIMAGE
GROUND MOVINGGROUND STATIONARY
SLIP
Results - velocity contours
Image Slip
Ground Stationary Ground Moving
Velocity Contours, H/c=0.025
0 37 14774 111
Image
Ground Moving
Slip
Ground Stationary
0 35 73 110 147
PIV Analysis
• Particle Image Velocimetry
• Pairs of images allow particle movement to be determined
• Nd-Yag laser, 532 nm, 100mJ/pulse
• Particles of spherical latex (5m)
• Initial investigation considered effect of moving ground
Moving Ground
Conveyor Belt
Wing
Drive System
Moving Ground
Camera
Conveyor Belt
Wing
Drive System
Moving Ground Stationary Ground
X X
Y Y
40
0 20 40 60 80 100 X
Y
60
40
20
0 0 20 40 60 80 100 X
Y
60
40
20
0
U 7.5 10 12
0 20 40 60 80 100 X 0 20 40 60 80 100 X
Y
60 40
20 0
Y
60 40
20 0
tke 0.25 0.50 1.0
Free Surface Effects
• Most WIG craft operate over water
• Lifting bodies produce a high pressure on their lower surface
• “Does this pressure change the surface shape, and does this affect the aerodynamic characteristics of the body?”
Free Surface Effects
• Froude number
• Reynolds number:
• CFD model (VOF) overcomes this issue
Uc
Re
gL
UFr
-0.025
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Froude Number
Su
rface
De
form
ati
on
(m
)Max Surface Deformation Beneath
Airfoil vs Froude Number
Importance of Viscous Effects
• Panel methods (inviscid) frequently used for ground effect
• Real flow situations – will viscous effects greatly affect results?
Results: Three-Dimensional
• NACA 4412 wing, AR=6
• Angles of attack:– 1.2O, 4O, 6.4O, 10O
• Reynolds Number:– 8,200,000
• Clearances (h/c):– 0.05, 0.10, 0.50, 1.00, free air
Effect of Ground on Separation
Mid-Semispan Plane Mid-Semispan Plane
h/c=0.05 h/c=free air
Effect of Ground on Wake
h/c=1.00
h/c=0.05
Moving Ground - wing
PIV Results – Flow separation
70 80 90X(mm)
0
10
20
30
Y(mm)
k1.500.750.00
70 80 90X(mm)
20
30
40
50
Y(mm)
k1.500.750.00
360 370 380 390 400 410 420 430 440 450X(mm)
10
20
30
40
50
60
70
80
90
Y(mm)
K6.003.000.00
360 370 380 390 400 410 420 430 440 450X(mm)
10
20
30
40
50
60
70
80
90
Y(mm)
K6.003.000.00
0 10 20 30 40 50 60 70 80 90X(mm)
0
10
20
30
40
50
60
70
80
90
Y(mm)
k4.002.000.00
0 10 20 30 40 50 60 70 80 90X(mm)
0
10
20
30
40
50
60
70
80
90
Y(mm)
k4.002.000.00
3 6 0 3 7 0 3 8 0 3 9 0 4 0 0 4 1 0 4 2 0 4 3 0 4 4 0 4 5 0X ( m m )
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
Y(m
m)
K6 . 0 03 . 0 00 . 0 0
3 6 0 3 7 0 3 8 0 3 9 0 4 0 0 4 1 0 4 2 0 4 3 0 4 4 0 4 5 0X ( m m )
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
Y(m
m)
K6 . 0 03 . 0 00 . 0 0
0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0X ( m m )
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
Y(m
m)
k4 . 0 02 . 0 00 . 0 0
0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0X ( m m )
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
Y(m
m)
k4 . 0 02 . 0 00 . 0 0
7 0 8 0 9 0X ( m m )
0
1 0
2 0
3 0
Y(m
m)
k1 . 5 00 . 7 50 . 0 0
7 0 8 0 9 0X ( m m )
2 0
3 0
4 0
5 0
Y(m
m)
k1 . 5 00 . 7 50 . 0 0
PIV tke CFD tkeNACA 4412 wing at 12o, h/c=0.45,
trailing edge region
PIV tke CFD tkeNACA 4412 wing at 12o, h/c=0.05,
trailing edge region
Moving Ground
- Implementation of moving ground into 3ft x 4ft wind tunnel - Belt speed of 60m/s- Extensive CFD analysis to determine best
configuration- Uniform velocity profile- Uniform turbulence profile
Moving Ground - suspended
Velocity Contours
Moving Ground – suspended, leadup
Velocity Contours
Moving Ground, in line
Velocity Contours
Moving Ground, offset, leadup, suction
Velocity Contours
Moving Ground - turbulence100
50
0
Moving Ground – design & construction
Supersonic Ground Effect
Shock Wave Validation Cases
Stationary Ground Supersonic Ground Effect
(Experimental)
Stationary Ground Supersonic Ground Effect
(CFD)
Moving Ground Supersonic Ground Effect
(CFD)
Integration of CFD & Experiments
CFD
ExperimentReal World
CFD GLUE
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