College of Engineering

Aerodynamic Effects of Painted Surface Roughness on Wind Turbine Blade

Performance

06/09/2015 Liselle A. Joseph

Aurelien Borgoltz Matthew Kuester

William Devenport

Julien Fenouil

Special thanks to Wind Turbine Aerodynamics Team of GE Power and Water

Joseph et al. NAWEA Symposium 2015

• Roughness is known to §  decrease lift (Abbott and Von Doenhoff, 1959; Jones, 1936) §  Increase drag (Abbott and Von Doenhoff, 1959; Jones, 1936) §  Move transition forward (Timmer, 2004)

• Roughness on wind turbine blades (icing, soiling, coat deterioration etc.) reduces performance (Sagol, 2013; Ehrmann, 2014; Dalili et al., 2009)

• These are the main types of roughness currently under study

• No work into the effect of orange-peel type roughness §  Likened to surface of an orange §  More wavy than peaky §  Produced from painting techniques and manufacturing processes

Importance of Roughness Effects

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Joseph et al. NAWEA Symposium 2015

• Created by painting Contact© paper with latex paint using rollers of various types

• Number of coats and painting direction were also varied

• 3 configurations created and tested

(a) (b) (c)

Images of the Roughness Configurations (a) S1 (b) S2 and (c) S3. The scale of the roughness features is illustrated using the 12.5-mm grid superimposed on the S1 roughness

12.5mm 12.5mm

Roughness Fetches

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Joseph et al. NAWEA Symposium 2015

• Approximate values of roughness parameters measured using Mahr PS1

• In order of increasing roughness heights: baseline, S1, S2, S3

Baseline

(Unpainted Contact© Paper)

S1 S2 S3

𝑅↓𝑎 ,  µμm 1.6 4.0 6.1 10.7

𝑅↓𝑡 ,  µμm 13.5 28.6 38.7 62.9

𝑅↓𝑞 ,  µμm 2.9 10.1 17.7 23.4

Roughness Fetches

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Joseph et al. NAWEA Symposium 2015

Chord (m) Re (x106) Configuration Rek1

0.8

2

baseline 0.4

S1 4.4

S2 12.7

S3 21.3

3

baseline 0.7

S1 7.9

S2 22.5

S3 37.5

0.46

1.5 baseline 0.7

S3 24.0

2 baseline 1.1

S2 48.2

•  Two DU96-W-180 models tested, each at 2 chord Reynolds Numbers

•  Smooth and rough cases tested for each model

•  Roughness Reynolds Number formulations:

•  Below Rek1,crit effects are small, above Rek1,crit effects become more noticeable

Re↓k1 = 𝑅↓𝑞 𝑢↓k /𝜈 

Test Matrix

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Joseph et al. NAWEA Symposium 2015

• Experiments done in VT stability Wind Tunnel

• Lift and drag obtained from pressure measurements from test section wall and drag rake

• Transition obtained from infrared transition detection system

• Model wrapped in contact paper, 0.8-mm insulator, then roughness fetch

Experimental Set Up

0.8-mm silicone rubber insulator Starboard

m o u n t e d IR camera

Drag rake

Port mounted IR camera

Downstream View of 0.80-m DU96-W-180 Mounted in Wind Tunnel with Infrared Thermography System

Aluminum model with internally mounted heaters

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Joseph et al. NAWEA Symposium 2015

• Positive stall: αc~ 9°to10°

• Negative stall: αc~-14°

• Zero-lift αc~ -2°

• Baseline cases for two models of different chord lengths agree

Results

-20 -15 -10 -5 0 5 10 15 20-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

αc

Clw

c

0.80-m DU96 Re=2.0M, baseline, Rek1=0.4

0.46-m DU96, Re=2.0M, baseline, Rek1=1.1

Variation of Lift and Drag for Different Chord Length Models, in Baseline Configuration, at Fixed Chord Reynolds Number of 2.0x106

-15 -10 -5 0 5 100

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

αc

Cdw

c

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Joseph et al. NAWEA Symposium 2015

• Max lift and lift curve slope decrease with increasing Rek1

• effect most apparent at positive αc, especially above αc=5°

• Above Rek1 ~ 23 effect of roughness becomes much larger than below this value

• Rek1crit ~ 23

Effect of Roughness on Lift

Lift Plots for Varying 𝑅𝑒↓𝑘1   for the DU96-W-180 (0.46-m and 0.80-m chords) at  𝑅𝑒↓𝑐    between 1.5x106 and 3.0x106

-15 -10 -5 0 5 10

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

αc

Clw

c

c=0.80m, Rec=2.0.M, baseline, Rek1=0.4

c=0.80m, Rec=3.0M, baseline, Rek1=0.7

c=0.46m, Rec=1.5M, baseline, Rek1=0.7

c=0.46m, Rec=2.0M, baseline, Rek1=1.1

c=0.80m, Rec=3.0M, S1, Rek1=7.9

c=0.80m, Rec=2.0M, S2, Rek1=12.7

c=0.80m, Rec=2.0M, S3, Rek1=21.3

c=0.80m, Rec=3.0M, S2, Rek1=22.5

c=0.46m, Rec=1.5M, S3, Rek1=24.0

c=0.80m, Rec=3.0M, S3, Rek1=37.5

c=0.46m, Rec=2.0M, S2, Rek1=48.2

6 8 10 120.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

αc

Clw

c

6 8 10 120.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

αc

Clw

c

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Joseph et al. NAWEA Symposium 2015

• Drag in bucket increases with increasing Rek1

• effect most dominant at positive αc

• Above Rek1 ~ 24 effect of roughness becomes much larger than below this value

• Rek1crit is between 20-25 (accounting for 10% uncertainty)

Effect of Roughness on Drag

-15 -10 -5 0 5 100

0.005

0.01

0.015

0.02

0.025

0.03

αc

Cdw

c

c=0.80m, Rec=2.0.M, Rek1=0.4

c=0.80m, Rec=3.0M, Rek1=0.7

c=0.46m, Rec=1.5M, Rek1=0.7

c=0.46m, Rec=2.0M, Rek1=1.1

c=0.80m, Rec=3.0M, Rek1=7.9

c=0.80m, Rec=2.0M, Rek1=12.7c=0.80m, Rec=2.0M, Rek1=21.3

c=0.80m, Rec=3.0M, Rek1=22.5

c=0.46m, Rec=1.5M, Rek1=24.0

c=0.80m, Rec=3.0M, Rek1=37.5

c=0.46m, Rec=2.0M, Rek1=48.2

Drag Plots for Varying 𝑅𝑒↓𝑘1   for the DU96-W-180 (0.46-m and 0.80-m chords) at  𝑅𝑒↓𝑐   

between 1.5x106 and 3.0x106

-15 -10 -5 0 5 100

0.005

0.01

0.015

0.02

0.025

0.03

αc

Cdw

c

c=0.80m, Rec=2.0.M, Rek1=0.4

c=0.80m, Rec=3.0M, Rek1=0.7

c=0.46m, Rec=1.5M, Rek1=0.7

c=0.46m, Rec=2.0M, Rek1=1.1

c=0.80m, Rec=3.0M, Rek1=7.9

c=0.80m, Rec=2.0M, Rek1=12.7c=0.80m, Rec=2.0M, Rek1=21.3

c=0.80m, Rec=3.0M, Rek1=22.5

c=0.46m, Rec=1.5M, Rek1=24.0

c=0.80m, Rec=3.0M, Rek1=37.5

c=0.46m, Rec=2.0M, Rek1=48.2

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Joseph et al. NAWEA Symposium 2015

• Below Rek1~23 L/Dmax slowly declines

• Large decrease in L/Dmax after Rek1~23

• Rek1crit ~ 20-25

Effect of Roughness on Lift-to-Drag Ratio

0 10 20 30 40 500

20

40

60

80

100

120

Rek1

L/D m

ax

datacurve fit

Variation of Maximum Lift-to-Drag Ratio with 𝑅𝑒↓𝑘1   for the DU96-W-180 (0.46-m and 0.80-m chords) at  𝑅𝑒↓𝑐    between 1.5x106 and

3.0x106 10/14

Joseph et al. NAWEA Symposium 2015

• Infrared transition detection system used to detect transition

• Gradient observed in images is onset of transition

• Image processing techniques used to extract %chord location AOA=0

IR Trans region ~56%(8.5" from TE)

AOA=0

IR Trans region ~61%(7.5" from TE)

Infrared Images of the Pressure Side of the 0.46-m DU96-W-180 at AoA=0° showing the Forward Movement of the Transition Front from the (a) Baseline case with Ra=1.58 to (b) S3 Roughness

case with Ra=6.78

FLOW

(a) (b)

Effect of Roughness on Transition

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Joseph et al. NAWEA Symposium 2015

-10 -5 0 5 100

10

20

30

40

50

60

70

80

α, dg

x/c,

%

Rec=2.0M, Rek1=0.4

Rec=3.0M, Rek1=0.7

Rec=2.0M, Rek1=4.4

Rec=3.0M, Rek1=7.9

Rec=2.0M, Rek1=12.7

Rec=2.0M, Rek1=21.3

Rec=3.0M, Rek1=22.5

Rec=3.0M, Rek1=37.5

-8 -6 -4 -2 0 2 4 6 8 10 1210

20

30

40

50

60

70

80

90

100

α, dg

x/c,

%

Rec=2.0M, Rek1=0.4

Rec=3.0M, Rek1=0.7

Rec=2.0M, Rek1=4.4

Rec=3.0M, Rek1=7.9

Rec=2.0M, Rek1=12.7

Rec=2.0M, Rek1=21.3

Rec=3.0M, Rek1=22.5

Variation of transition location with angle of attack on the (a) Suction and (b) Pressure Side of the 0.8-m for all Rek1

Effect of Roughness on Transition

Suction Side Pressure Side

0.8-m DU96-W-180

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Joseph et al. NAWEA Symposium 2015

-10 -5 0 5 100

10

20

30

40

50

60

70

80

α, dg

x/c,

%

Rec=1.5M, Rek1=0.7

Rec=1.5M, Rek1=24.0

Rec=2.0M, Rek1=48.2

-10 -5 0 5 100

10

20

30

40

50

60

70

80

α, dg

x/c,

%

Rec=1.5M, Rek1=0.7

Rec=2.0M, Rek1= 1.1

Rec=1.5M, Rek1= 24.0

Rec=2.0M, Rek1= 48.2

Variation of transition location with angle of attack on the (a) Suction and (b) Pressure Side of the 0.46-m for all Rek1

Effect of Roughness on Transition Suction Side Pressure Side

0.46-m DU96-W-180

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Joseph et al. NAWEA Symposium 2015

Orange-peel type painted surface roughness on wind turbine blades have an effect on the performance

It was found that: • Roughness effects show dependence on Rec and Rek

• The effect of the roughness is more pronounced at positive angles of attack

• Lift decreases gradually with increasing Rek, up to the critical Rek

• Drag increases gradually with increasing Rek, up to the critical Rek

• Transition moves forward slightly with increasing Rek, up to the critical Rek

• Critical Rek for orange-peel roughness is between 20 and 25.

Conclusions

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Q&A

Joseph et al. NAWEA Symposium 2015

Supporting Slides

Joseph et al. NAWEA Symposium 2015

Effect of Roughness on T-S Waves  

• Roughness induced disturbances grow and overtake natural T-S waves

• Roughness-induced T-S waves cause linear transition front upstream of natural transition

0 2 4 6 8 10 12 14 16 180

0.2

0.4

0.6

0.8

1

1.2

1.4x 10

-3

Wavelength, mm

Nor

mal

ized

PSD

S1S2S3

Averaged wavelength spectra of the painted roughness surfaces

0 5 10 15 20 25 30 35 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength, mm

Norm

alize

d Inte

grate

d Gro

wth

0.46-m chord, Re = 1.5x106

0 5 10 15 20 25 30 35 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength, mm

Norm

alize

d Inte

grate

d Gro

wth

0.46-m chord Re = 2.0x106

0 5 10 15 20 25 30 35 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength, mm

Norm

alize

d Inte

grate

d Gro

wth

0.80-m chord, Re = 2.0x106

0 5 10 15 20 25 30 35 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength, mm

Norm

alize

d Inte

grate

d Gro

wth

0.80-m chord, Re = 3.0x106

α = -5 deg., Pressure Side: x/c=10%α = 0 deg., Pressure Side: x/c=50%α = 5 deg., Pressure Side: x/c=70%α = -5 deg., Suction Side: x/c=55%α = 0 deg., Suction Side: x/c=50%α = 5 deg., Suction Side: x/c=40%

Wavelengths of unstable Tollmien-Schlichting disturbances for (a) 0.46-m DU96-W-180 at Re=1.5x106 and (b) 0.80-m DU96-W-180 at Re=1.5x106

(a)

(b)

Joseph et al. NAWEA Symposium 2015

Analysis of Effect on Performance • XFOIL used to investigate whether changes in lift and drag are from changes in transition

• XFOIL ‘tripped’ at where transition is observed on IRT images for rough cases

• Differences compared to that observed between clean and rough results

-10 -5 0 5 10-1

-0.5

0

0.5

1

1.5

α, deg.

Cl

-10 -5 0 5 100.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

α, deg.

Cd

-10 -5 0 5 10-0.5

0

0.5

1

1.5

2

2.5

3

3.5x 10

-3

α, deg.

ΔC

d

-10 -5 0 5 10-0.07

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

α, deg.

ΔC

l

Clean - ExperimentS3 - ExperimentClean - XFOILS3 - XFOIL

ΔCl - ExperimentΔCl - XFOIL

ΔCd - ExperimentΔCd - XFOIL

XFOIL analysis of the effect of transition location on lift and drag. XFOIL transition locations were set from IR transition measurements for the 0.46-m DU96-W-180 Model at Re = 1.5x106. Differences in (a)

lift and (b) drag are between the clean model (covered in insulator) and the S3 roughness condition.

(a) (b)