Convective Heat Transfer and
Experimental Icing Aerodynamics of Wind
Turbine Blades
Xin Wang
Ph.D. Oral Examination
Department of Mechanical & Manufacturing
University of Manitoba
May 07, 2008
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
OUTLINE
 Introduction
 Experimental procedure




Wind Tunnel with spray water system
Power measurement
Aerodynamic test
Temperature measurement
 Results and Discussion
 Power losses due to icing events
 Icing affected lift and drag
 Heat transfer coefficients at varying AOA with and
without LWC
 Conclusions
 Acknowledgements
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Introduction




Climate change
Rising energy demand
Reduction of GHG emissions
Wind energy penetration
 up to 12% by 2020
 Annual increase of 14.2%
 Cumulative growth rate
 19% prediction
140
120
100
80
60
40
20
0
2005 2006 2007 2008 2009 2010
Unit: GW (in the world)
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Wind energy in cold climates
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Wind icing issues
 Reduced power
Wind energy in cold
climates consortium
 Icing factor
 Safety issue
 Ice fragments
 Wear and tear
 Excess vibration
Copyright: http://virtual.vtt.fi/virtual/arcticwind/index.htm
Affects Canadian wind farms
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Wind tunnel in UM
 Icing Wind Tunnel
 Velocity up to 42 m/s
 Temperature down to -35oC
insulated
walls
fan cabinet
turning vanes
motor
air
flow
heat
exchanger
fan
contraction
section
plenum,
screens
refrigeration
piping
heated
window
test
chamber
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Wind turbine blades
• Blade fabrication
•
•
•
•
Scanned the blade by 3-D Scanner
Processed by Geomagic Studio
Optimized the blade by Inventor
Fabricated by Prototype machine
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Wind turbine for Power loss test
 3-blade wind turbine model
 3 blades made of resin
 Generator: permanent magnet DC
 144 W 48 V
 Manufactured Hub
 Adjustable hub center: 2.8°/washer
 Material: Brass
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Water spraying system
 Water cooling system
 Set up temperature same as the flow
 Water spray system




4 atomizing nozzles
Air pressure 50 psi
Water pressure 35 psi
Flow control
Variable Heaters:
• Wide: 40 mm; Length: 880 mm
• Power: 0 to 500 W
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Measurements by LabVIEW
Voltage transducer
Current Transducer
DAQ Software:
LabVIEW 8
•
Temperature
•
Voltage, Current
•
Rotation
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Force balance installation
Force balance wall right side
Shaft couples
Hand wheel
Movable duct
Tunnel Block
Shaft protector
Shaft holder
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Aerodynamic test models
 Airfoil dimensions:




2×62.5 mm in span
500 mm in chord
Thickness of airfoil: 105 mm
Surface material: fiber glass
 Cylinder dimensions:
 Diameter 110 mm
 Length: 125 mm
 Material: PVC
Force Balance
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Force measurement
• Allied force balance：
• Measured:
FX, FZ, MX, MY, MZ
• Time: 1 /second
• Calibrated by April 2006
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Temperature measurement model
 Airfoil dimensions:
 3×62.5 mm in span (tested airfoil in the centre)
 500 mm in chord
 3 mm in thickness
 Temperature measurements:
 T type thermocouples with build-in
compensation
80
T5
60
T3
40
h3
h4
T7
h2
T8
T8
T6
T4
T9
h5
T 11
T 10
h6
 22 in airfoil
 3 in tunnel
 2 to measure zero point cell as reference
 3 inside spray bar to monitor nuzzle temperature
20
T1
0
-20
-40
-60
T 2 h1
T 12
T 20
0
T 19
h10
100
T1
T 17
h9
T 14 300
200
T 16
T 15
T 13
h8
400
h7
500
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Temperature measurement
Hardware connection for measuring
Temperature and power (left)
Temperature reading when
measured (below, front panel of
Labview)
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Power output at different pitch angles
 Reynolds Number:
u D
Re D 

Where:

D = diameter of wind turbine m,

ρ = density of free stream kg/m3,

u = velocity of free stream m/s
μ = viscosity of free stream m2/kg.
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Power output with glaze ice
1
P/P*
0.8
0.6
-2℃
2m
δ = 0 mm (20°C)
δ = 0.12mm (-1°C)
δ = 0.72 mm (-1°C)
δ = 3.5 mm (-1°C)
δ = 7.2 mm (-1°C)
δ = 9.4 mm (-1°C)
-2℃
5m
0.4
-2℃
10 m
0.2
Comparison of Rotation
1.3
Comparison rotation δ = 0 mm (20°C)
0
6.5E+05
1.2E+06
1.7E+06
1.1
2.2E+06
Glaze iced wind turbine
Comparison of power
RPM/RPM*
ReD
0.9
δ = 0.12 mm (-1°C)
δ = 0.72 mm (-1°C)
δ = 3.5 mm (-1°C)
δ = 7.2 mm (-1°C)
δ = 9.4 mm (-1°C)
0.7
0.5
0.3
0.1
6.5E+05
1.2E+06
1.7E+06
ReD
2.2E+06
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Affected power by rime ice

Rime iced wind turbine
Power losses at extreme icing conditions
2.2
δ = 0 mm (20°C)
1.8
δ = 5.6 mm (-30°C)
δ = 8.5 mm (-30°C)
P/P*
1.4
δ = 12.7 mm (-30°C)
1
2
0.6
δ = 0 mm (20°C)
1.6
0.2
δ = 5.6 mm (-30°C)
-0.2
6.0E+05
1.1E+06
1.6E+06
2.1E+06
ReD
Iced wind turbine blade
2.6E+06
RPM/RPM*
δ = 8.5 mm (-30°C)
1.2
δ = 12.7 mm (-30°C)
0.8
0.4
Iced wind turbine blade
0
6.0E+05 1.1E+06 1.6E+06 2.1E+06 2.6E+06
ReD
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Summary of power losses with ice
 Ice affects the power output significantly.
 Iced blades with different aerodynamic
characteristics
 Extreme ice conditions will make wind
turbines provide more power up to 190%
higher than rated power outputs.
 More research needed for iced airfoils.
 Anti-icing or de-icing needed for extreme
weather conditions.
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Ice shape over the airfoil
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Glaze ice shapes
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Glaze ice shapes
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Rime ice shapes
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Rime ice shapes
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Aerodynamics of glaze iced airfoils
0.25
0.2
AOA = 0 (15 mins)
AOA = 0 (30 mins)
AOA = 0 (45 mins)
AOA = 3 without ice
AOA = 3 (15 mins)
AOA = 3 (30 mins)
AOA = 3 (45 mins)
AOA = 6 without ice
AOA = 6 (15 mins)
AOA = 6 (30 mins)
AOA = 6 (45 mins)
CL
0.15
AOA = 0 without ice
0.1
0.05
0
8.0E+05
9.0E+05
1.0E+06
Re
1.1E+06
1.2E+06
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Aerodynamics of rime iced airfoils
0.25
CL
0.2
AOA = 0 without ice
AOA = 0 (15 mins)
AOA = 0 (30 mins)
AOA = 0 (45 mins)
AOA = 6 without ice
AOA = 6 (15 mins)
AOA = 6 (30 mins)
AOA = 6 (45 mins)
AOA = 6
AOA = 0
0.15
0.1
0.3
8.0E+05
9.0E+05
1.0E+06
1.1E+06
1.2E+06
Re
0.25
Aerodynamics at various AOA
AOA = 3 without ice
AOA = 3 (15 mins)
AOA = 3 (30 mins)
AOA = 3 (45 mins)
AOA = 9 without ice
AOA = 9 (15 mins)
AOA = 9 (30 mins)
AOA = 9 (45 mins)
0.2
CL
0.05
7.0E+05
0.15
AOA = 9
AOA = 3
0.1
0.05
7.0E+05
8.0E+05
9.0E+05
1.0E+06
Re
1.1E+06
1.2E+06
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Summary of iced shapes and aerodynamics
 Ice shapes over the airfoil obtained by
MatLAB
 Ice shapes are different between glaze
ice and rime ice at same conditions
 The Reynolds number affects the lift
coefficient at low value
 With ice thicknesses increasing, the lift
coefficient will drop
 The lift coefficient increases when the
airfoil obtains some ice thickness
 The drag coefficient increases when the
airfoil obtains ice accretion.
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Formulations of heat transfer
 Convective heat transfer
 Conductive heat transfer
qcon  h(T0  T )
qcon  qcd 
k (Tin  To )

k (Tin  T0 )
 Heat transfer coefficient h 
 (T0  T )
 Average coefficient
1
1 11
h   hdx   hi si
ss
s i
 Average Nusselt number
Nu 
hc
k air
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Experimental Data at AOA=0
900
800
700
Nu
600
500
Pr=0.7098
Pr=0.7125
Pr=0.7152
Pr=0.7166
Pr=0.7181
Pr=0.7196
Pr=0.7211
Pr=0.7226
Local Nusselt number at
varying chord positions
(x/c) (Below)
2000
400
1800
300
1600
0.0E+00
4.0E+05
8.0E+05
1.2E+06
Re
1400
1.6E+06
1200
Nux
200
Re=186,000
Re=330,000
Re=478,868
Re=620,112
Re=757,878
Re=897,117
Re=1,037,270
Re=1,170,358
Re=1,435,573
Re=1,304,821
1000
Average Nusselt number at
varying Reynolds and Prandtl
numbers (Above)
800
600
400
200
0
-0.6
-0.3
0
0.3
0.6
Non-dimensional chord position
0.9
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Comparison: NACA airfoil, flat plate,
cylinder
4000
Measured (Pr=0.7195)
Measured (Pr=0.7152)
3200
Flat Plate (low Re)
Flat Plate (high Re)
Cylinder (Churchill correlation)
Cylinder (Hilpert correlation)
Nu
2400
1600
800
0
0.0E+00
4.0E+05
8.0E+05
Re
1.2E+06
1.6E+06
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Modified Hilpert Correlations (AOA=0)
• Hilpert correlation for a cylinder in cross
flow Nu  c Rem Pr1/3
• Modified Hilpert correlations for an airfoil
Normalized Nusselt function correlation
without LWC
• Nu  2.483Re0.389 Pr1/3
for Re ≤ 5 × 105
• Nu  0.0943Re0.636 Pr1/3
for Re＞5 × 105
8
Ln( Nu/Pr^(1/3))
7.5
7
6.5
Pr=0.709
Pr=0.712
Pr=0.715
Pr=0.717
pr=0.718
Pr=0.720
Pr=0.721
Pr=0.722
Pr=0.721, c=0.0943, m=0.636
Pr=0.718, c=0.0943, m=0.636
Pr=0.718, c=2.48, m=0.389
Pr=0.712, c=2.48, m=0.389
6
5.5
11.5
12
12.5
13
Ln(Rec)
13.5
14
14.5
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Measured data and Nusselt number at various AOA
1100
Measured α = 5
Measured α = 15
Measured α = 25
Modified α = 10
Modified α = 20
Predicted α = 0
1000
Nu (average)
900
800
Measured α = 10
Measured α = 20
Modified α = 5
Modified α = 15
Modified α = 25
1100
1000
900
800
700
700
600
600
500
500
400
400
300
(for Re > 5 × 105)
5.0E+05
7.0E+05
9.0E+05
1.1E+06
Pr
1
3
Nu (average)
450
Nu  0.0943(0.75  0.017 ) Re
Nu  2.483(0.75  0.013 ) Re
300
550
1.3E+06 1.5E+06 Measured (AOA= 5°)
Rec
0.636
Low Re (Below)
0.389
Pr
Measured (AOA=10°)
Measured (AOA=20°)
Predicted (AOA= 5°)
Predicted (AOA=15°)
Predicted (AOA=25°)
Measured (AOA=15°)
Measured (AOA=25°)
Predicted (AOA=10°)
Predicted (AOA=20°)
Predicted (AOA= 0°)
1
3
550
450
350
350
250
250
150
150
High Re (Above)
1.2E+05
2.2E+05
3.2E+05
Rec
4.2E+05
5.2E+05
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Comparison of data with LWC and Nusselt correlations
800
LWC=0.15-0.29
750
LWC=0.3-0.399
LWC=0.4-0.65
0.636
Pr1/3
Nu=0.0943Re
650
Low Re (Below)
600
550
500
450
a)
550
400
6.0E+05
7.0E+05
8.0E+05
9.0E+05
Re
LWC=(0.4-0.49)
1.0E+06
500 1.1E+06
LWC=(0.5-0.8)
450
High Re (Above)
Nu (average)
Nu (Average)
700
400
LWC=(0.9-2)
Nu=2.483 Re
0.389
Pr1/3
350
300
250
b)
200
1.0E+05
2.0E+05
3.0E+05
Re
4.0E+05
5.0E+05
6.0E+05
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Application non-dimension of LWC
800
Nu=0.0943 (Re(1+W))
0.636
Pr1/3
700
600
Nu  2.483(Re(1  W ))0.389 Pr1/ 3
500
Re(1+W) ＜ 6 × 105
400
500
300
6.0E+05
8.0E+05
1.0E+06
1.2E+06
1.4E+06
1.6E+06
Re(1+W)
W 
Nu =2.483(Re(1+W))
0.389
Pr1/3
Expermental data
Nu (Average)
Nu (Average)
Eperimental data
LWC
LWC0
400
300
Nu  0.0943(Re(1  W ))0.636 Pr1/ 3
Re(1+W) > 6 ×
105
200
2.0E+05
3.0E+05
4.0E+05
Re(1+W)
5.0E+05
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Modified Hilpert Correlation with LWC at varying AOA
1000
900
800
700
900
Re(1+W) ≤ 6 × 105
800
700
600
Nu  2.483(0.75  0.01 )(Re(1  W ))
600
Nu  0.0943(Re(1  W ))0.636 Pr1/ 3
500
400
6.0E+05
500500
400
8.0E+05
1.0E+06 1.2E+06
Re(1+W)
Nu  0.0943(1  0.007 )(Re(1  W ))
1.4E+06
0.636
1.6E+06
1
Pr 3
Nu (average)
Nu (average)
1000
Measured AOA=5°
Measured AOA=10°
Measured AOA=15°
Measured AOA=20°
Measured AOA=25°
Predicted AOA=5°
Predicted AOA=15°
Predicted AOA=10°
Predicted AOA=20
Predicted AOA=25°
Predicted AOA=0°
400
0.389
1
Pr 3
500
Measured AOA=5°
Measured AOA=10°
Measured AOA=15°
Measured AOA=20°
Measured AOA=25°
Predicted AOA=0°, 25°
Predicted AOA=10°
Predicted AOA=15°
Predicted AOA=20°
Predicted AOA=5°
400
Nu  2.483(Re(1  W ))0.389 Pr1/ 3
300
300
Re (1+W) > 6 × 105
200
2.0E+05
3.0E+05
4.0E+05
Re(1+W)
5.0E+05
200
6.0E+05
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Summary of convective heat transfer
 Modified Hilpert Correlations at 0 AOA and
various AOA from 0° to 25°without LWC.
 The multiphase Reynolds parameter is
shown to provide normalization against
single-phase correlations over a wide range
of Reynolds numbers at different AOA.
 Heat transfer can be calculated by using
modified Hilpert Correlations.
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Summary of convective heat transfer
 Heat transfer coefficients AOA = 0
Nu  2.483Re0.389 Pr1/3
Re ≤ 5 × 105
Nu  0.0943Re0.636 Pr1/3
Re > 5 × 105
 Convective heat transfer at various AOA
Nu  2.483(0.75  0.013 ) Re0.389 Pr
Nu  0.0943(0.75  0.017 ) Re
0.636
1
1
Re ≤ 5 × 105
3
Re > 5 × 105
 Multiphase Reynolds parameter without AOA
W 
Pr
3
LWC
LWC0

Nu  2.483(Re(1  W ))0.389 Pr1/ 3
Re (1+W) ≤ 6 × 105
Re (1+W) > 6 × 105
Nu  0.0943(Re(1  W ))0.636 Pr1/ 3
 Modified Hilpert Correlations with LWC at varying AOA
Nu  2.483(0.75  0.01 )(Re(1  W )) 0.389 Pr
Nu  0.0943(1  0.007 )(Re(1  W )) 0.636 Pr
1
3
1
3
Re (1+W) ≤ 6 × 105
Re (1+W) > 6 × 105
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Conclusions
 Wind power losses under icing conditions
 ice will reduce power output progressively as the ice thickness
increases
 Ice accretion changes profile of blades
 Iced wind turbine would increase power output under extreme
cold climate
 Iced shapes and aerodynamics of the airfoil
 ice shapes on an airfoil are different under glaze and rime ice
conditions
 Glaze ice shapes are smooth and rime iced shapes are rough
 The aerodynamics of an iced airfoil was slightly affected by the
higher Reynolds number
 The ice shapes decide the lift drop or increase as well as ice
always make drag increase
 Convective heat transfer
 Modified Nusselt number correlation at varying AOA
 Heat transfer coefficients with and without LWC
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Acknowledgements
• Natural Sciences and Research
Council of Canada (NSERC)
• Canada Foundation for
Innovation (CFI)
• Manitoba Hydro/NSERC
Industrial Research Chair in
Alternative Energy
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Thanks for your attention
Questions ?
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Journal Publications
1.
X. Wang, E. Bibeau, G. F. Naterer, 2008, “Wind Tunnel Study of
Convective Heat Transfer from a NACA Wind Turbine Blade at
Varying Angles of Attack,” AIAA Journal of Thermophysics and
Heat Transfer (in press).
2.
Wang, X., Naterer, G. F.，Bibeau, E., 2008, “Multiphase Nusselt
Correlation for the Impinging Droplet Heat Flux from a NACA Airfoil,”
AIAA Journal of Thermophysics and Heat Transfer, vol. 22, no. 2,
pp. 219 – 226.
3.
X. Wang, G. F. Naterer, E. Bibeau, 2007, “Convective droplet
impact and heat transfer from a NACA airfoil,” Journal of
Thermophysics and Heat Transfer, vol. 21, no. 3, pp. 543 - 547.
4.
X.Wang, E. Bibeau G. F. Naterer, 2007, “Experimental Correlation
of Forced Convection Heat Transfer from a NACA Airfoil,”
Experimental Thermal and Fluid Science, vol. 31, no. 8, pp. 10731082.
Convective Heat Transfer and Experimental Icing of Wind Turbine Blades
Conference publications
1.
2.
3.
4.
5.
6.
7.
X. Wang, E. L. Bibeau, G. F. Naterer, 2008, “Multiphase flow with
convective droplet impact on a NACA airfoil at varying Angles of attack,”
46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, U.S.A,
Jan. 10.
X. Wang, E. L. Bibeau, G. F. Naterer, 2007, “Experimental Investigation of
Energy Losses due to Icing of a Wind Turbine,” International Conference
on power engineering-2007, Hangzhou, China, Oct 23-27.
X. Wang, G. F. Naterer, E. Bibeau, 2007, “Wind tunnel measurements of
convective heat transfer with droplet impact on a wind turbine NACA63-421
blade,” 2007 ASME-JSME Thermal Engineering Conference and Summer
Heat Transfer Conference, Vancouver, BC, Canada, July 8-12.
Wang, X., Bibeau, E., Naterer, G. F., 2007, “Modified Hilpert Correlation for
Turbulent Convective Heat Transfer from a NACA Profile of Wind Turbine
Blades,” AIAA 39th Thermophysics Conference, Miami, FL, June 25 – 28.
X. Wang, E. Bibeau, G. F. Naterer, 2006, “Experimental investigation of
wind energy losses under icing Conditions,” Canada Wind Energy
Association Conference, Winnipeg, Oct. 22-25. Poster presentation.
X. Wang, G. F. Naterer, E. Bibeau, 2006, “Experimental study of 3-D
blades and wind turbines under icing conditions,” The Second International
Green Energy Conference, Oshawa, Ontario, June 25 - 29.
Wang, X., Xu, T., Wang, J., 2004, “Experimental Study of Aerodynamic
Fields of α-shaped Flame,” The 4th International Symposium on
Measurement Techniques for Multiphase Flows, Huangzhou, China, Oct.