36
The VAWT in Skew:
Stereo-PIV and Vortex Modeling
ir. C.J. Simão Ferreira, M.Sc. K. Dixon, Dipl.-Ing. C. Hofemann, Prof. Dr. ir. G.J.W. van Bussel, Prof. Dr. ir. G. A.M. van Kuik
47th AIAA Aerospace Sciences Meeting 5 - 8 Jan 2009, Orlando World Center MarriottOrlando, Florida
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
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x M
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• Who
• What
• Why
• How
• Where
• Result
s
Carlos, Kristian, Claudia, ...
Numerical & Experimental…
Effect of the skewed angle on wake
Upwind & Downwind blade passage
To understand the influence of the skew angle on the performance of the VAWT
Vertical Axis Wind Turbine (VAWT)
Table of contents
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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What ? VAWT
The
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in S
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: S
tere
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IV a
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Skewed flow ->
Misalignment of the flow perpendicular to the ground
What VAWT in Skew
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing Why ?
VAWT operating under skewed flow
show a higher efficiency than VAWT
operating under normal conditions !
Why ?
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing How ? Numerical
3D unsteady free wake panel method
• Design and research tool
– capturing the 3D nature of a VAWT and its wake
• Allows to analyze the effect of skew in terms of
– bound circulation,
– shed and trailing vorticity
– torque, wake and flow asymmetry
• Validated by PIV and Smoke Trail Studies
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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How ? Numerical
The
VA
WT
in S
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: S
tere
o-P
IV a
nd V
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x M
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Two blades:
NACA 0015 (trailing edge) NACA 0018 (quarter chord)
Tip speed ratio:
λ = 4
Wind speed:
10 m/s
Reynolds number:
8 x 10 4
How ? Experimental
l = 700 mm Z
X
Y
d= 570 mm
c = 60 mm
The
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IV a
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Wind
Y
X
Z
How ?
Low speed /Low turbulence Wind Tunnel
The
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How ? 3D-Stereo-PIV
The
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: S
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IV a
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Where ? Upwind & Downwind
X
Y
0°
90°
180°measuring planes
wind
-120 mm
-0.42 y/R
120 mm
0.42 y/R
upwinddownwind
Numerical Upwind & Downwind Experimental Downwind
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
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Results ? Tip vortex locus (Exp.)
Skew angles: = +20 = 0 = - 20
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
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Results ? Tip vortex locus (Sim.)
Skew angles: = +20 = 0 = - 20
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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Results ? Tip vortex locus
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
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x M
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Results ? Location of the wake
Azimuth angle:
= 90
Skew angles:
• = +20
• = 0
• = - 20
The
VA
WT
in S
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: S
tere
o-P
IV a
nd V
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x M
odel
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Results ? Trailing vorticity
Skew angles:
• = +20
• = 0
• = - 20
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
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Results ? Shed vorticity
Skew angles:
• = +20
• = 0
• = - 20
The
VA
WT
in S
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: S
tere
o-P
IV a
nd V
orte
x M
odel
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Results ? Bound vorticity
Skew angles:
• = +20
• = 0
• = - 20
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
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x M
odel
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Results ? Normal Force
Skew angles:
• = +20
• = 0
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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Results ? Trailing vorticity
Skew
angles:
• = 0
• = 10
• = 20
• = 30
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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Results ? Shed vorticity
Skew
angles:
• = 0
• = 10
• = 20
• = 30
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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Results ? Tangential Force
Skew
angles:
• = 0
• = 10
• = 20
• = 30
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing
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Results ? Validation
The
VA
WT
in S
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: S
tere
o-P
IV a
nd V
orte
x M
odel
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Conclusions ?• The impact of the skew angle on the wake has
been shown by the 3D panel method • Skewed flow
– increases the performance of the VAWT– generates an asymmetry of the wake in z-direction– causes asymmetry of the expansion of the wake in y-
direction
• 3D unsteady free wake panel code – is able to replicate the effect of skew– shows the impact of the skew angle on the strength of
the wake for trailing and shed vorticity– shows the effect on bound vorticty as well as on normal
and tangential forces – is not able to capture the roll of motion
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
orte
x M
odel
ing Questions ?
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The
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: S
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Results ? Induction in x-direction
Skew angles:
• = +20
• = 0
• = - 20
The
VA
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in S
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: S
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IV a
nd V
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x M
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Results ? Induction in z-direction
Skew angles:
• = +20
• = 0
• = - 20
The
VA
WT
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: S
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o-P
IV a
nd V
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x M
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Why ?
The
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Δt
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How ? Stereo PIV / Displacement
The
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NACA 0018: leading edge quarter chord
NACA 0015:flat tip trailing edge
What ? Blade configuration
The
VA
WT
in S
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: S
tere
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IV a
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x M
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ing Where ?
32
Wind
Y
X
Z
The
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-60 mm
rotational
directions
X
Y
0°
90°
180°
measuring planes
wind
-180 mm
-120 mm
120 mm
180 mm
60 mm
upwinddownwind
Where ?
The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
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x M
odel
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How ? Stereo PIV
Method:
• indirect
• monitoring due to tracer particles
• the displacement is pictured via two images, taken within Δt
• Stereo -> 2 cameras (rotated) to quantify the out of plain motions
Z
XY
x
y
zLaser
The
VA
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in S
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: S
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o-P
IV a
nd V
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x M
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How ? Data Reduction
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The
VA
WT
in S
kew
: S
tere
o-P
IV a
nd V
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x M
odel
ing
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How ? Evaluation
Methode:
• longest vorticty level
• Integration over the enclosed area ( )
C SVds V ds
