Dr. Dr. HuiHui HUHUAdvanced Flow Diagnostics and Experimental Aerodynamics LaboratoAdvanced Flow Diagnostics and Experimental Aerodynamics Laboratoryry
Department of Aerospace Engineering, Iowa State UniversityDepartment of Aerospace Engineering, Iowa State University2251 Howe Hall, Ames, IA 500112251 Howe Hall, Ames, IA 50011--22712271
Email: Email: [email protected]@iastate.edu
An Experimental Investigation on Surface Water Transport and IceAn Experimental Investigation on Surface Water Transport and IceAccreting Process Pertinent to Wind Turbine Icing Phenomena Accreting Process Pertinent to Wind Turbine Icing Phenomena
Wind Turbine Icing and AntiWind Turbine Icing and Anti--/De/De-- IcingIcing
•• Wind turbine icing Wind turbine icing represents the most significant threat to the integrity of represents the most significant threat to the integrity of wind turbines in cold weather. wind turbines in cold weather. –– Change airfoil shapes of turbine blades.Change airfoil shapes of turbine blades.–– Cause imbalance to the rotating system.Cause imbalance to the rotating system.–– Shedding of large chuck of ice can be dangerous to public safetyShedding of large chuck of ice can be dangerous to public safety..–– Cause errors to anemometers to estimate wind resource.Cause errors to anemometers to estimate wind resource.
•• Some Some thermal dethermal de‐‐icing systems icing systems could consume up to could consume up to 70%70% of the total power of the total power generated by the wind turbine on cold days.generated by the wind turbine on cold days.
• Glaze ice is the most dangerous type of ice.
• Glaze ice form much more complicated shapes and are difficult to accurately predict.
• Glaze ice is much more difficult to remove once built up on aircraft wings or wind turbine blades.
Rime Ice and Glaze IceRime Ice and Glaze Ice
a)a)
b)b)
Oncoming air Oncoming air flow with flow with supercooledsupercooledwater dropletswater droplets
Glaze ice formation
Rime ice formation
Surface Tension Surface Tension IInduced Flow nduced Flow -- MaragoniMaragoni Flow Flow inside Water Dropletsinside Water Droplets
Temperature of Plate, Temperature of Plate, TTWallWall=21.9 =21.9 OOC C Video was taken at f=0.5hz; ReVideo was taken at f=0.5hz; Re--play speed is f=5hzplay speed is f=5hz
((HuHu and Jin, and Jin, Int. J. of Multiphase Flow, Vol. Int. J. of Multiphase Flow, Vol. 36, No.8, pp67236, No.8, pp672––681681, 2010, 2010))
a)a)
b)b)Incoming flow Incoming flow with superwith super--cooled water cooled water dropletsdroplets
Incoming flow Incoming flow with superwith super--cooled water cooled water dropletsdroplets
Molecular Tagging Thermometry Technique (MTT) to Quantify the TiMolecular Tagging Thermometry Technique (MTT) to Quantify the Time me Evolution of the Droplet Cooling and Evaporation ProcessEvolution of the Droplet Cooling and Evaporation Process
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
60 70 80 90 100 110 120 130 140 150 160 17040
45
50
55
60
65
70
Droplet volume, VDroplet heigth, hContact angle
Time (second)
V/V
o , h/
h o
Con
tact
ang
le (d
egre
es)
((HuHu and Huang, AIAA Journal, Vol. 47, No.4, and Huang, AIAA Journal, Vol. 47, No.4, pp813pp813--820, 2009820, 2009 ))
H
R
VWater droplet
Solid surface
)(tan2 1
RH
3
23
sin3)cos2()cos1(
RV
m
m
-400 -200 0 200 400
0
200
400
5.0 7.0 9.0 11.0 13.0 15.0 17.0 19.0 21.0
Temperature(OC)
Test Plate (T=5.0OC)
0
2
4
6
8
10
12
14
16
18
0 5 10 15 20 25 30 35 40
Curve fitExperimental data
Time (s)
Tem
pera
ture
(OC
)
Test plate, T=5.0 Test plate, T=5.0 OOCC
a).a). The first phosphorescence image acquired The first phosphorescence image acquired at 0.5ms after excitation laser pulseat 0.5ms after excitation laser pulse
b).b). The second phosphorescence image acquired The second phosphorescence image acquired at 3.5ms after the same excitation laser pulseat 3.5ms after the same excitation laser pulse
Test plate, Test plate, T=5.0 T=5.0 OOCC
~280~280mm
Phase Change Process within An Icing Water DropletPhase Change Process within An Icing Water Droplet
Test Plate, Tw = -2.0OC Test Plate, Tw = -2.0OC Test Plate, Tw = -2.0OC Test Plate, Tw = -2.0OC
~250mt = 0.5 s
Solid ice
Liquid water
t = 5.0 s t = 20.0 s t = 35.0 s
X (m)
Y(
m)
-400 -200 0 200 400
0
200
4000.0 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0
Test Plate (TW=-2.0OC)
t = 0.5 s
Temperature(OC)
X (m)
Y(
m)
-400 -200 0 200 400
0
200
4000.0 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0
Test Plate (TW=-2.0OC)
t = 5.0 s
Temperature(OC)
X (m)
Y(
m)
-400 -200 0 200 400
0
200
4000.0 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0
Test Plate (TW=-2.0OC)
t = 20.0 s
Temperature(OC)
X (m)
Y(
m)
-400 -200 0 200 400
0
200
4000.0 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0
Test Plate (TW=-2.0OC)
t = 35.0 s
Temperature(OC)
Unsteady heat transfer and phase changing process inside small iUnsteady heat transfer and phase changing process inside small icing water dropletscing water droplets
Instantaneous phosphorescence imagesInstantaneous phosphorescence images
((HuHu and Jin, and Jin, International Journal of Multiphase Flow, 36(8):672–681, 2010))
Surface Water Transport in Glaze Ice Accretion ProcessSurface Water Transport in Glaze Ice Accretion Process
•• Collaborating with Dr. Collaborating with Dr. AlricAlric RothmayerRothmayer @ Iowa State University@ Iowa State University
Numerical simulation results of surface water transport Numerical simulation results of surface water transport (Wang & (Wang & RothmayerRothmayer, Computers and Fluids 2009). , Computers and Fluids 2009).
Glaze ice accreting process over a NACA0012 airfoil (Waldman anGlaze ice accreting process over a NACA0012 airfoil (Waldman and d HuHu, 2014), 2014)
Flow Flow directiondirection
VV
Videos of ice accretion
α ≈ 5.0 deg.
ISU Icing Research TunnelISU Icing Research Tunnel
ISUISU--Icing Research Tunnel (ISUIcing Research Tunnel (ISU--IRT)IRT)
•• The ISU Icing Research Tunnel (ISUThe ISU Icing Research Tunnel (ISU--IRT), IRT), originally donated by originally donated by UTC Aerospace System ( formerly Goodrich Corp.), is a researchUTC Aerospace System ( formerly Goodrich Corp.), is a research--grade multigrade multi--functional icing wind tunnel. functional icing wind tunnel.
•• The working parameters of the ISUThe working parameters of the ISU--IRT include: IRT include: •• Test section:Test section: 16 inches by 16 inches by 6 ft16 inches by 16 inches by 6 ft•• Velocity: Velocity: up to 60m/s;up to 60m/s;•• Temperature: Temperature: down to down to --30 30 OOC;C;•• Droplet Size: Droplet Size: 10 to 100 micrometers;10 to 100 micrometers;•• Liquid Water Content (LWC): Liquid Water Content (LWC): 0.05 ~ 20 grams/cubic meter. 0.05 ~ 20 grams/cubic meter.
•• The large LWC range allows ISUThe large LWC range allows ISU--IRT tunnel to be run over a IRT tunnel to be run over a range of conditions from rime ice to extremely wet glaze ice.range of conditions from rime ice to extremely wet glaze ice.
0
2
4
6
0 2 4 6
Linear curve fittingmeasurement data
Phase difference, (radians)
Hei
ght (
mm
)
K=1.0266 mm/pixel
Displacement (pixel)
height (mm
)
Digital Image Projection (DIP) technique Digital Image Projection (DIP) technique (USA Patent Pending)(USA Patent Pending)
Reference imageReference image Deformed image due to the existence of a Deformed image due to the existence of a semisemi--sphere on the reference planesphere on the reference plane
CAKCAdsBDyxZ ),(
Height distributionHeight distribution
CameraProjector
Vertical Translation Stage
Target plate
Host computer
Z
Y
X
Transient Behavior of Wind Transient Behavior of Wind ––Driven Water Film/Rivulet Flows for Icing Physics Study Driven Water Film/Rivulet Flows for Icing Physics Study (Funded by NASA and NSF)(Funded by NASA and NSF)
((HuHu et al. 2011, Experiments in Fluids)et al. 2011, Experiments in Fluids)
-5
0
5
10
15
20
0 1 2 3 4 5 6 7 8 9
rear end of the droplet/rivuletfront end of the droplet/rivulet
Time (s)
Mov
ing
spee
d of
the
cont
act l
ine
(mm
/s)
0
0.5
1.0
1.5
2.0
2.5
0 1 2 3 4 5 6 7 8 9
V/VoS/So
Time (s)
Wet
Sur
face
Are
a (S
/So),
Dro
plet
/Riv
ulet
Vol
ume
(V/V
o)
-2
0
2
4
6
-8 -4 0 4 8 12 16 20 24 28 32 36
Measured Droplet/Rivulet Thickness
Downstream Distance (mm)
Dro
plet
/Riv
ulet
Thi
ckne
ss (m
m)
t = t0+5.0s
-2
0
2
4
6
-8 -4 0 4 8 12 16 20 24 28 32 36
Measured Droplet/Rivulet Thicknessy=0
Downstream Distance (mm)
Dro
plet
/Riv
ulet
Thi
ckne
ss (m
m)
t = t0
-2
0
2
4
6
-8 -4 0 4 8 12 16 20 24 28 32 36
Measured Droplet/Rivulet Thicknessy=0
Downstream Distance (mm)
Dro
plet
/Riv
ulet
Thi
ckne
ss (m
m)
t = t0+1.0s
Contact line moving Contact line moving speed vs. timespeed vs. time
Wet area on the test plate & droplet Wet area on the test plate & droplet /rivulet volume (mass) vs. time/rivulet volume (mass) vs. time
Time Evolution of a WindTime Evolution of a Wind--Driven Droplet/Rivulet Flow over a Flat Surface Driven Droplet/Rivulet Flow over a Flat Surface
•• HuHu et al., AIAAet al., AIAA--20122012--0261,0261, 20122012
Effects of various important parameters:Effects of various important parameters:•• Temperature of the surfaceTemperature of the surface•• Thermal conductivity of the subtractsThermal conductivity of the subtracts•• Roughness of the test surfacesRoughness of the test surfaces•• Surface Surface hydrophobicityhydrophobicity•• Coatings or Coatings or nanonano--structures on the test surfacesstructures on the test surfaces•• ……. .
Boundary layer airflow Boundary layer airflow Boundary layer airflow
Transient Behavior of Wind Transient Behavior of Wind ––Driven Water Film/Rivulet FlowsDriven Water Film/Rivulet Flows(Dry Surface Condition)(Dry Surface Condition)
•• Water flow rate: Water flow rate: Q= 100 ml/minQ= 100 ml/min•• Free stream airflow: Free stream airflow: VV∞∞=20m/s =20m/s
•• Water flow rate: Water flow rate: Q= 100 ml/minQ= 100 ml/min•• Free stream airflow: Free stream airflow: VV∞∞=15m/s =15m/s
•• Water flow rate: Water flow rate: Q= 100 ml/minQ= 100 ml/min•• Free stream airflow: Free stream airflow: VV∞∞=10m/s =10m/s
Experimental conditions:Experimental conditions:smV /20~10
min/0.1 mlQ Incoming flow velocity: Incoming flow velocity: Water flow rate:Water flow rate:Spray droplet size:Spray droplet size: 50um~10D
Incoming Incoming flowflow
Digital image projector
Digital camera
Spray nozzles
Water droplets
NACA0012 airfoil
incoming airflow
Picture of the test section in the icing wind tunnelPicture of the test section in the icing wind tunnel
WindWind--driven Water Runback Flow over a NACA 0012 Airfoildriven Water Runback Flow over a NACA 0012 Airfoil
(Zhang K. and Hu H., AIAA(Zhang K. and Hu H., AIAA--20142014--0741,0741, 2014)2014)
MicroMicro--sized Water Droplets Impinging onto a NACAsized Water Droplets Impinging onto a NACA--0012 Airfoil0012 Airfoil
•• Test ConditionsTest Conditions•• Angle of attack of the airfoil:Angle of attack of the airfoil: αα ≈≈ 0.0 deg. 0.0 deg. •• Temperature of the wind tunnel :Temperature of the wind tunnel : T T ≈≈ 20 20 °°C.C.•• The liquid water content (LWC) : The liquid water content (LWC) : LWC =5.0 g/mLWC =5.0 g/m33
•• Frame rate for Image acquisition: Frame rate for Image acquisition: f = 30 Hzf = 30 Hz
Airflow velocityAirflow velocity
V=20m/sV=20m/sAirflow velocityAirflow velocity
VV =15m/s =15m/s Airflow velocityAirflow velocity
VV =20m/s =20m/s
Airflow velocityAirflow velocity
VV =25m/s =25m/s
VV =15m/s=15m/s VV =20m/s=20m/s VV =25m/s=25m/s
Water Runback Flow over a NACA 0012 AirfoilWater Runback Flow over a NACA 0012 Airfoil
• V = 10m/s • V = 15m/s • V = 20m/s • V = 25m/s
Velocity of the oncoming airflow(m/s)
Transition location from film flows to rivulet flows
(% airfoil chord length)
Averaged width of the rivulet flows(% airfoil chord
length)
Averaged gap between the rivulet flows (% airfoil
chord length)
10.0 51.5 13.64 >35
15.0 44.2 9.51 17.41
20.0 35.3 4.92 10.23
25.0 27.1 3.03 6.34
30.0 25.2 1.97 5.19
• V = 10m/s
• V = 20m/s
Water Runback Flow over a NACA 0012 AirfoilWater Runback Flow over a NACA 0012 Airfoil
S x=0.13c
• Feo (2001) and Rothmayer (2003) all suggested that wind- driven water film thickness would follow a x1/4law :
Water Runback Scaling Laws:Water Runback Scaling Laws:
Hu et al., AIAA Journal (2015), submittedHu et al., AIAA Journal (2015), submitted
Glaze Ice Accreting Process over a NACA0012 AirfoilGlaze Ice Accreting Process over a NACA0012 Airfoil
• Test Conditions• Oncoming airflow velocity : V ≈ 20 m/s• Angle of attack of the airfoil: α ≈ 5 deg. • Temperature of the wind tunnel : T ≈ ‐8 °C.• The liquid water content (LWC) : LWC =3.0 g/m3
• Total recording time : t = 110 seconds
Frame rate for Image acquisition, f = 150Hz, 10X replay
Upper surface
Lower surface
VV
Videos of ice accretion
α ≈ 5.0 deg.
(Waldman R. and Hu H.,(Waldman R. and Hu H., 2015, Journal of Aerocraft, submitted)2015, Journal of Aerocraft, submitted)
Glaze Ice Accreting Process over a NACA0012 AirfoilGlaze Ice Accreting Process over a NACA0012 Airfoil
VV∞∞= 40 m/s= 40 m/s
VV∞∞= 60 m/s= 60 m/s
VV∞∞= 20 m/s= 20 m/s
•• TT ∞∞ = = -- 8.0 8.0 °°C; C; •• = 5 = 5 °°; ; •• LWC = 1.1 g/mLWC = 1.1 g/m33
(Waldman R. and Hu H.,(Waldman R. and Hu H., 2015, Journal of Aircraft , submitted)2015, Journal of Aircraft , submitted)
IR Thermometry to Quantify the Unsteady Heat Transfer ProcessIR Thermometry to Quantify the Unsteady Heat Transfer Process
Incoming Incoming airflowairflow
•• Experimental Conditions: Experimental Conditions: VV∞∞= 35 m/s; = 35 m/s; TT ∞∞ = = -- 8.0 8.0 °°C; C; AoA= 5 AoA= 5 °°; ; LWC = 3.0 g/mLWC = 3.0 g/m33
B AD CE
B AD CE
•• Experimental Conditions: Experimental Conditions: VV∞∞= 35 m/s; = 35 m/s; TT ∞∞ = = -- 8.0 8.0 °°C; C; AOA = 5 AOA = 5 °°; ; LWC = 0.30 g/mLWC = 0.30 g/m33
(Liu Y. and Hu H.,(Liu Y. and Hu H., 2015, AIAA Journal, submitted)2015, AIAA Journal, submitted)
Rime ice accretion
Glaze ice accretion
Hydrophilic, Hydrophobic and Hydrophilic, Hydrophobic and SuperhydrophobicSuperhydrophobic
a). drop on a smooth surface; b). Wenzel state; c). a). drop on a smooth surface; b). Wenzel state; c). CassieCassie––Baxter state; d). combined state.Baxter state; d). combined state.
Measured Measured θθ = 67 [deg]= 67 [deg]
Measured Measured θθ = 170 [deg]= 170 [deg]Measured Measured θθ = 104 [deg]= 104 [deg]
•• Hydrophilic;Hydrophilic; < 90 < 90 oo •• Hydrophobic;Hydrophobic; 90 90 oo << < 150 < 150 oo •• SuperhydrophobicSuperhydrophobic; ; > 150 > 150 oo
Lotus leaves
Effects of Surface Effects of Surface HydrophobicityHydrophobicity on Surface Water Transport and Ice on Surface Water Transport and Ice Accretion ProcessAccretion Process
Anti-icing of superhydrophobicsurface in “freezing rain”
reported by Cao et al. (2009)
•• Surface engineering to change the surface Surface engineering to change the surface hydrophobicityhydrophobicity of the of the airfoils/wings for wind turbine antiairfoils/wings for wind turbine anti--/de/de--icing applicationsicing applications
Anti- icing coating test on wind turbines
Surface Chemistry: Effects of Surface Chemistry: Effects of HydrophobicityHydrophobicity of the Airfoil Surface of the Airfoil Surface on the on the Impingement of Water Droplets ( Weber number ~ 800 )Impingement of Water Droplets ( Weber number ~ 800 )
45 degree slope
With Super-hydrophobic Surface coating
Without Super-hydrophobic Surface coating Without Super-hydrophobic
Surface coating
With Super-hydrophobic Surface coating
Acquired at 12K FPS, replay at 400X slower
Normal impact
Without Super-hydrophobic Surface coating
With Super-hydrophobic Surface coating
Without Super-hydrophobic Surface coating
With Super-hydrophobic Surface coating
Surface Chemistry: Effects of Surface Chemistry: Effects of HydrophobicityHydrophobicity of the Airfoil Surface of the Airfoil Surface on the on the Impingement of Water DropletsImpingement of Water Droplets
Thank you Very Much for Your Time!Thank you Very Much for Your Time!Questions?Questions?
Upper surface
Lower surface
WindWind--driven water film flow over a NACA0012 airfoil pertinent to aircdriven water film flow over a NACA0012 airfoil pertinent to aircraft icing (Zhang and raft icing (Zhang and HuHu, 2014), 2014)
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