National Rotor Testbed Design Christopher L. Kelley Sandia National Laboratories 31st August 2016 The document discusses the design of wind turbine blades for the Scaled Wind Farm Technology facility. The objective was to design blades that would produce a wake similar to a full-scale 1.5 MW turbine. An inverse design tool was used to determine the chord and twist distributions needed to match the circulation of the full-scale turbine. Computational fluid dynamics simulations confirmed the blades would produce the desired wake. The blades will be 3D printed and tested at the facility to study wind turbine wakes.

1. National Rotor Testbed Design
Christopher L. Kelley
Sandia National Laboratories
31st August 2016

2. Motivation
• To better understand wind turbine wakes
• Use SWiFT experimental facility
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3. Aerodynamic Objective
• Design wind turbine blades to be manufactured and flown
for research on wakes in an array
• Create same initial conditions velocity/momentum deficit at
rotor plane as fullscale machine
• What shape does the blade need to produce scaled wake?
2

4. A Scaled Wake
3

5. How Is a Wake Created?
Γ
r
R
=
Γ( r
R )
RU∞
=
Cl
2
W
U∞
c
R
• Circulation is
proportional to lift
• Lift forces determine
shed circulation
4

6. Objective Function, Γfs
• most common wind turbine in USA, GE 1.5sle, GE37c
• full-scale turbine model provided by manufacturer
• modeled in WT_Perf
• λ = 9
• smooth surface airfoil data from wind tunnel
5

7. Objective Function, Cl
• for a given circulation, Cl determines local solidity
• adequate stall margin
• efficient L/D
• smooth chord and twist distribution
• Cl = 0.6
Γ
r
R
=
Cl
2
W
U∞
c
R
6

8. Airfoil Selection Criteria
• Rec ≈ 2,000,000
• high quality, public, and low turbulence wind tunnel data
• fixed transition, roughness, and unsteady data
• roughness insensitivity
• thickness requirements
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9. Airfoil Selection
S814 (t
c = 0.24) and S825 (t
c = 0.17)
Cd
0 0.01 0.02 0.03
Cl
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
S825 Re 1E6
S825 Re 2E6
S825 Re 3E6
S825 Re 4E6
S825 Re 6E6
S814 Re 0.7E6
S814 Re 1E6
S814 Re 1.5E6
S814 Re 2E6
S814 Re 3E6
, [deg]
-5 0 5 10 15 20
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10. Inverse Design
• created inverse
design tool
• solved for chord and
twist
• iterate with WT_Perf
RMSE Γ
0.08 0.085 0.09 0.095 0.1
RMSEα
0
0.2
0.4
0.6
0.8
9

11. Circulation
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12. Geometry
r/R
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
c/R
0
0.05
0.1
subscale
V27
C
Pmax
r/R
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
β[deg]
0
5
10
15
subscale
V27
C
Pmax
11

13. NRT Blade
12

14. NRT Blade
(nrtu3d.u3d)
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15. Performance
Wind speed (m/s)
4 6 8 10 12 14
Power(kW)
0
20
40
60
80
100
120
140
160
180
200
Wind speed (m/s)
4 6 8 10 12 14 16
β(deg)
0
2
4
6
8
10
12
X: 11.11
Y: 195
X: 7.65
Y: 63.97
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16. Performance
D [m] λR2 σ [%] Prated [kW] CPR2
CTR2
Pr(R2) Pr(R2.5) Pr(R3) cf AEP [GWh]
27 9 6.4 195 0.462 0.863 0.49 0.30 0.05 0.30 0.51
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17. Free Wake Vortex Simulation
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18. Momentum Recovery
17

19. 3D CFD, 11 m/s
2D BEMT agrees with 3d CFD separation location
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20. 3D CFD
3D flow effects and uncertainty of root section performance not
an issue
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21. 3D Printed Blade Mold at Oakridge
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22. Conclusions
• inverse design tool implemented to design blades to
produce a specific wake
• blade geometry creates scaled wake of commercial 1.5 MW
turbine
• 3D CFD indicates no issues in using 2D for blade root for
this design
• NRT blade to be flown at SWiFT and used for wake
experiments
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