Airfoil Design

03 May, 2004 1DUWIND, section Wind Energy, Faculty CiTG

Design of Airfoils for Wind Turbine Blades

Ruud van Rooij([email protected])

Nando Timmer

Delft University of TechnologyThe Netherlands


Delft University of Technology13200 Bsc+ Msc students, 4750 employees

Delft University Wind Energy Research Institute(Coordinator: Section Wind Energy)

Faculties:• Civil Engineering and Geosciences (Wind Energy, Offshore)

http://www.windenergy.citg.tudelft.nl/home/flash/index.html

• Information Technology and Systems (Electrical group)

• Design, Engineering and Production (Systems &Control)

• Aerospace Engineering (Aero, Aeroelastics)


Section Wind Energy (Civil Engineering and Geosciences => Aerospace Engineering)

Aerodynamic research

- Facilities

open-jetwind tunnel research wind turbine

low speed wind-tunnel


Contents

• Background

• Design goals HAWT airfoils

• Design approach• Performance comparison

• Airfoil testing

• Effect on wind turbine power Cp

• Overview HAWT airfoils


Background

Operational area

High Cp80% of Energy

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 5.0 10.0 15.0 20.0 25.0

W inds speed (m /s)

Pow er

Variable RPMControl: Power restriction

High max. L/DAirfoil: Max. lift considerations


Background

Blade geometry

- High max. L/D- Insensitive to

roughness- Similar design

angle

Airfoil:

- High max. lift(Rot. Effects)

No Aerodynamicdemands

Outboard: t/= .15-18

Mid span: t/= .25

Inboard: t/> .30

Structural:

Transition piece


Background

Effect of rotation

RFOIL code

• Integral boundary layer eq.

• Extended for radial flow• Radial equations• Cross flow profile

parameter is c/r(= local solidity)

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

-5.0 0.0 5.0 10.0 15.0 20.0 25.0

Angle (deg.)

cl

DU 91-W2-250Re = 3.0x10e6

2d

mid-span

inboard

Stall delay


Design goals HAWT airfoilssteady

Low noise

.21 >.28 - .21> .28Thickness-to-chord ratio

High maximum lift-to-drag ratio

Structural demands

Geometric compatibility

Insensitivity to roughness

Low max. and benign post stall


Design approach(example DU 91-W2-250)

DU 91-W2-250

NACA 63-425

Main features

S-Tail => Aft-loading

Small upper surface thickness => reduced roughness sensitivity


Design approach(pressure distributions DU 91-W2-250, Re = 3.0x106)

- 4. 0

- 3. 0

- 2. 0

- 1. 0

0. 0

1. 00.0 0.2 0.4 0.6 0.8 1.0x/c

Cp

Separation

Aft-loading

TransitionAlpha= 0.0o

7.0o

11.0o

Low roughness sensitivity=> Transition at nose for Cl_max

Low drag=> Aft transition at Cl_design


-0.50

0.00

0.50

1.00

1.50

0 50 100 150cl/cd

cl

-0.50

0.00

0.50

1.00

1.50

-5.0 0.0 5.0 10.0 15.0 20.0Angle (deg.)

cl

DU 91-W2-250

NACA 63-425Re = 3.0x106

Airfoil design(2d performance)

Design lift

Measurements at LST-TU Delft: Clean


-0.50

0.00

0.50

1.00

1.50

0 30 60 90cl/cd

cl

-0.50

0.00

0.50

1.00

1.50

-5.0 0.0 5.0 10.0 15.0 20.0Angle (deg.)

cl

DU 91-W2-250

NACA 63-425Re = 3.0x106

Airfoil design(2d performance)

Design lift

Measurements at LST-TU Delft: Roughness simulatedZZ-Tape at 5% u.s.


Airfoil testing(Low speed low turbulence tunnel)

Test section size 1.80 x 1.25 mMaximum speed 120 m/sTurbulence level 0.015% at 10 m/s

0.07% at 70 m/s

Test section


Airfoil testing(effect of leading edge thickness)

-0.4

0

0.4

0.8

1.2

1.6

-5 0 5 10 15 20 25 30 35 40

angle of attack (degrees)

Lift

coef

ficie

nt

Re=1.0x106

DU 97-W-300

DU 96-W-180


Airfoil testing(effect of high Reynolds numbers)

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 5 10Re x10-6

0

20

40

60

80

100

120

0 5 10Re x10-6

Clean

Zigzag tape 0.4 mm

Carborundum 60

Airfoil: DU 97-W-300Mod

(Cl/Cd)max Cl,max


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000

Airfoil testing(360 degrees)


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α=24o


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α= 40o

Cl= 1.145



-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000

α=90o

Cl= 0.10 Cd= 1.914


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α= 160o

Cl= -.627


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α= 194o

Cl= 0.541


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α= 224o

Cl= 0.811


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α= 270o

Cl= -0.11 Cd= 1.832


-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50 0 50 100 150 200 250 300 350 400

angle of attack

Cl, Cd

DU 96-W-180

Re=700,000


α= 316o

Cl=- 0.971


Airfoil testing (aerodynamic devices)

• Stall strips Ø 1.2 mm

DU 93-W-210 R = 2.0x106

-1.0

-0.5

0.0

0.5

1.0

1.5

0.00 0.01 0.02 0.03cd

cl

-1.0

-0.5

0.0

0.5

1.0

1.5

-10 0 10 20α ( o)

cl

no trip wire

wire at 0.5%c l.s.

wire at 0.25%c l.s.


-0.4

0.0

0.4

0.8

1.2

1.6

2.0

0.0 30.0 60.0 90.0 120.0Cl/Cd

Cl

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

-5.0 0.0 5.0 10.0 15.0 20.0 25.0Alpha (deg.)

Cl

VG at x/c= 0.2VG at x/c= 0.3Clean

DU 91-W2-250Re = 2.0x106

Airfoil testing (aerodynamic devices)

• Vortex generators


Effect on wind turbine performance(2d stationary performance)

Calculated optimal element performance at mid-span for TSR= 7.5

ZZ-tape 5% u.s.

CpLoadingCp_elem“Static load”Cl_max*c

L/D-maxc/RClean

-5.1%8%.532.155600.135DU 91-W2-250

-0.24%6%.560.1521190.119NACA 63-425

.212

0.143

0.149

.503

.561

.56

-10.2%48%390.212NACA 63-425

0%0%1250.105DU 91-W2-250

-0.06%4%1220.106AH 93-W-257

* “Static load” reference based on 1 year gust for fixed pitch blades


0.50

0.51

0.52

0.53

0.54

0.55

0.56

0.57

0 20 40 60 80 100 120 140max. L/D

local Aero Cp

Effect on wind turbine performance (2d stationary performance)

25% thick airfoil class (mid-span for TSR= 7.5)

“Rough”

DU 91-W2-250

-5%

NACA 63-425

-10%


Overview of HAWT airfoils

General aviation airfoils• NACA 63-4xx and NACA 63-6xx series• NACA 64-4xx

Dedicated airfoils• S8xx series (NREL, USA)

• FFA W-xxx (FOI, Sweden)

• Risø-A1-xxx (also B, P-series, Risø, Denmark)

• DU xx-W-xxx (Delft, Netherlands)


Overview of HAWT airfoils

• Overview of DU-airfoils and users

GE-Wind, REpower, Dewind, Suzlon, Gamesa, LM Glasfiber, NOI Rotortechnik, Fuhrlander, Pfleiderer, EUROS, NEG Micon, Umoe blades, Ecotecnia ……..

DU 97DU 97--WW--300300DU 96DU 96--WW--180180

DU 95DU 95--WW--180180

DU 93DU 93--WW--210210

DU 00DU 00--WW--212212DU 00DU 00--WW--350350

DU 91DU 91--W2W2--250250


Next steps:

Extending to all operational situations :

• Measurements => “high” Reynolds number=> chart unsteady behavior of DU airfoils

New airfoil designs :

• Very thick airfoils for lightweight blades

• Control of rpm only => Low TSRLow Cl-max, benign stall

=> High TSRLow drag

• Aero-elastic tailoring => Dynamic airfoil design(Probably low Cl-max)

Airfoil Design

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