National Rotor Testbed DesignChristopher L. KelleySandia National Laboratories31st August 2016

Motivation• To better understand wind turbine wakes• Use SWiFT experimental facility

1

Aerodynamic Objective• Design wind turbine blades to be manufactured and flownfor research on wakes in an array• Create same initial conditions velocity/momentum deficit atrotor plane as fullscale machine• What shape does the blade need to produce scaled wake?

2

A Scaled Wake

3

How Is a Wake Created?

Γ′( rR

)=

Γ( rR)

RU∞=Cl

2

W

U∞

c

R

• Circulation isproportional to lift• Lift forces determineshed circulation

4

Objective Function, Γ′fs

• 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

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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′( rR

)=Cl

2

W

U∞

c

R

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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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Airfoil SelectionS814 ( tc = 0.24) and S825 ( tc = 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 1E6S825 Re 2E6S825 Re 3E6S825 Re 4E6S825 Re 6E6S814 Re 0.7E6S814 Re 1E6S814 Re 1.5E6S814 Re 2E6S814 Re 3E6

, [deg]-5 0 5 10 15 20

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Inverse Design

• created inversedesign tool• solved for chord andtwist• iterate with WT_Perf

RMSE Γ

0.08 0.085 0.09 0.095 0.1

RM

SE

α

0

0.2

0.4

0.6

0.8

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Circulation

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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

CPmax

r/R

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

β [

de

g]

0

5

10

15

subscale

V27

CPmax

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NRT Blade

12

NRT Blade

(nrtu3d.u3d)

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Performance

Wind speed (m/s)4 6 8 10 12 14

Pow

er

(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: 11.11Y: 195

X: 7.65Y: 63.97

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Performance

D [m] λR2 σ [%] Prated [kW] CPR2CTR2

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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Free Wake Vortex Simulation

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Momentum Recovery

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3D CFD, 11 m/s

2D BEMT agrees with 3d CFD separation location

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3D CFD3D flow effects and uncertainty of root section performance notan issue

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3D Printed Blade Mold at Oakridge

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Conclusions

• inverse design tool implemented to design blades toproduce a specific wake• blade geometry creates scaled wake of commercial 1.5 MWturbine• 3D CFD indicates no issues in using 2D for blade root forthis design• NRT blade to be flown at SWiFT and used for wakeexperiments

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