Aerodynamic Effects of Painted Surface Roughness …...S1 4.4 S2 12.7 S3 21.3 3 baseline 0.7 S1 7.9...

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

2/14


• 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

3/14


• 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

4/14


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

5/14


• 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

6/14


• 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

7/14


• 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=0.80m, 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

8/14


• 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

9/14


• 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


• 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

11/14


-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

12/14


-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

13/14


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

14/14


Q&A


Supporting Slides


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)


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)

Aerodynamic Effects of Painted Surface Roughness …...S1 4.4 S2 12.7 S3 21.3 3 baseline 0.7 S1 7.9...

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