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The potentials of the controllable rubber trailing edge flap (CRTEF)Helge Aa. Madsen1 , Peter B. Andersen1, Tom L. Andersen2, Thomas Buhl1, Christian Bak1 and Mac Gaunaa1
Wind Energy Division1
Materials Research Division2
Risø National Laboratory for Sustainable EnergyTechnical University of Denmark, P.O. 49, DK-4000 Roskilde, Denmark.
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Risø DTU, Technical University of DenmarkRisø DTU, Technical University of Denmark
OUTLINE Background The CRTEF Wind tunnel test results Potential load reductions Summary and outlook
April 21. 2010
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Background non-uniform rotor loading from turbulence increases with
size of rotor a distributed control along the blade has advantages for
load alleviation and for stability control numerical studies (e.g. Buhl 2005 and Andersen 2009)
show considerable load reduction potentials using flap control
Buhl T, Gaunaa M, Bak C. Potential load reduction using airfoils with variable trailing edge geometry. Journal of Solar Energy Engineering 2005; 127: 503–516.
Andersen, P.B., Henriksen, L., Gaunaa, M., Bak, C., Buhl, T. ”Deformable trailing edge fl aps for modern megawatt wind turbine controllers using strain gauge sensors”. WIND ENERGY Wind Energ. (2009) Published online. DOI: 10.1002/we.371
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Risø DTU, Technical University of DenmarkRisø DTU, Technical University of Denmark
Background – flap technology What flap technology can be used ?
piezo electric flaps (Bak et al. 2007) deployable tabs (van Dam et al. 2007)
Bak C, Gaunaa M, Andersen PB, Buhl T, Hansen P, Clemmensen K, Møller R. Wind tunnel test on wind turbine airfoil with adaptive trailing edge geometry. [Technical Papers] Presented at the 42 AIAA Aerospace Sciences Meeting and Exhibit 45 AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 2007; 1–16.
van Dam CP, Chow R, Zayas JR, Berg DA. Computational investigations of small deploying tabs and flaps for aerodynamic load control. Journal of Physics 2007; 5. 2nd EWEA, EAWE The Science of Making Torque from Wind Conference, Lyngby, 2007; 1–10.
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The CRTEF Development work started in 2006
Main objective: Develop a robust, simple controllable trailing edge flap
The CRTEF design: A flap in an elastic material as e.g. rubber with a number of reinforced voids that can be pres-surized giving a deflection of the flap
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The CRTEF development
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Comsol 2D analyses
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Wind tunnel experiment
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the 2m airfoil section with the flap in the VELUX wind tunnel, December 2009
airfoil section + flap during instrumentation
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Wind tunnel experiment
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two different inflow sensors
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VELUX WIND TUNNEL EXPERIMENT
NACA0015 airfoil section withWITH RUBBER TRAILING EDGE FLAP
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5-c
p [-]
x/c [-]
MEAS: =2.4deg
MEAS: =-8.0deg
AOA=8deg
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0.1 Hz, beta step
DAY 1
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0 1 2 3 4 5 6 7 8 9 100.75
0.8
0.85
0.9
0.95
1
time [s]
CL [-
]
=8degFlap SG [deg]
0 1 2 3 4 5 6 7 8 9 10
-8
-6
-4
-2
0
2
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6
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10
12
[d
eg]
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0 50 100 150 200 250-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
t*=t/(c/V0) [-]
CL-C
L(=0
) [-]
=0deg=2deg=4deg=6deg=8deg=10deg=12deg
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A MODEL FOR THE RUBBER FLAP RESPONSE
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
2
4
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
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volt [V]pressure [bar]deflection [mm]model-volt [V]model-pressure [bar]model-deflection [mm]
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Aero-elastic simulationsSingle flap - 30% of the bladeControl input from simulated strain gaugeHomogenious turbulent inflow
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30 40 50 60 70 80 90 100 110 120 1302
4
6
8
Win
d [m
/s]
30 40 50 60 70 80 90 100 110 120 130-6000
-5000
-4000
-3000
root
mom
. [K
Nm
]
30 40 50 60 70 80 90 100 110 120 130-10
-5
0
5
10
flap
[deg
]
time [s]
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30 40 50 60 70 80 90 100 110 120 1304
6
8
10
12
Win
d [m
/s]
30 40 50 60 70 80 90 100 110 120 130-10000
-8000
-6000
-4000
-2000
root
mom
. [K
Nm
]
30 40 50 60 70 80 90 100 110 120 130-10
-5
0
5
10
flap
[deg
]
time [s]
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Summary and outlook
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the basic principle of functioning of the CRTEF has been proven
aerodynamic and aeroelastic characteristics documented through wind tunnel tests
first aeroelastic simulations using wind tunnel flap characteristic as input indicate 50 percent load reduction potential
new development project formulated to bring the CRTEF technology up to a stage where it is ready for testing on a fullscale MW turbine (time frame about 2 years)