47th Aerospace Science Meeting and Exhibit, Orlando, Florida, 20091 47 th AIAA Aerospace Science Meeting and Exhibit Orlando, Florida, 5-8 January 2009

47th Aerospace Science Meeting and Exhibit, Orlando, Florida, 2009 1

4747thth AIAA Aerospace Science Meeting AIAA Aerospace Science Meeting and Exhibitand Exhibit

Orlando, Florida, 5-8 January 2009Orlando, Florida, 5-8 January 2009

Anti-icing Materials International LaboratoryAnti-icing Materials International Laboratory

Wind Turbine Icing and De-Icing

Guy Fortin and Jean PerronGuy Fortin and Jean Perron Université du Québec à ChicoutimiUniversité du Québec à Chicoutimi


OverviewOverview

INTRODUCTION ICING EVENT FORMATION WATER COLLECTION ICE ACCRETION WIND TURBINE ICE PROTECTION SYSTEMS CONCLUSION


IntroductionIntroduction

Atmospheric Icing

Ice accretes on structure (overhead cables, pylons, satellite dishes, communication towers, airplanes, helicopters, wind turbines, offshore drilling rigs, ships, docks, bridges, roads, dams, buildings…) causing of great damages to electric lines, telecommunication networks, in the maritime, road and air transport, causing materials damages and human safety risk.


IntroductionIntroduction

Problem Description

• Wind turbine atmospheric icing a) Ice accumulates on the rotor bladesb) Reducing aerodynamic efficiency leading to

a) less power production.b) vibration c) ice sheddingd) wind turbine stope) worst case, blades collapse


Icing Event FormationIcing Event Formation

Atmospheric Icing

Icing occurs when hot air mass meet an air mass below freezing leading to hydrometeors such as

1. Freezing drizzle2. Freezing rain3. Wet snow

Or in presence of1. Cloud in altitude (> 400 m)2. Fog at ground level

When temperature is below freezing


0

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0 10 20 30 40 50 60 70 80 90 100

Diameter (µm)

Fre

qu

en

cy (

%)

Diameter Volume

MVD = 20.8 µm


Atmospheric Icing

Hydrometeors are characterized by1. Liquid Water Content which is the quantity of

water contained in the air expressed as g/m³.2. Median Volumetric Diameter of water droplet

which is a representative value of the water droplet distribution expressed as µm.

0

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1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101

105

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Diameter (µm)

Dro

plet

Fre

quen

cy (

%)



Atmospheric Icing

How ice accrete on blade


Water CollectionWater Collection

Water Collection

The first parameters to evaluate ice accretion is the Impingement Mass

Collection EfficiencyAir Speed

Impingement Surface

Liquid Water Content

impaimp AULWCE m

sup

inf

1 s

sds

HE

Local Collection Efficiency

Impingement Distance



Water Collection

Lower LimitLocal Collection Efficiency

Upper Limit

0

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-0.16 -0.14 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06

Curvilinear Abscissa

Lo

cal C

olle

ctio

n E

ffic

ien

cy

Stagnation Point

dy

ds



Water Collection

Water Droplet Trajectory Calculations1. Droplets are spherical2. No collision or coalescence3. Small water droplet concentration.

gvvK

C

dt

vd

w

ada

d

dDd

11

24

Re

Drag Gravity Buoyancy

Reynolds Number Inertia Parameter



Water Collection

Local collection efficiency increases when the Median Volumetric Diameter increase

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-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1


Lo

cal C

olle

ctio

n E

ffic

ien

cy

MVD = 10 µm MVD = 20 µm MVD = 50 µm



Water Collection

Local collection efficiency decrease when the Chord increase

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-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1


Lo

cal C

olle

ctio

n E

ffic

ien

cy

Chord = 0.5 m Chord = 1.0 m Chord = 3.0 m



Water Collection

Local collection efficiency increase when the Speed increase

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-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1


Lo

cal C

olle

ctio

n E

ffic

ien

cy

U = 15 m/s U = 30 m/s U = 67 m/s



Water Collection

Local collection efficiency increases when the Angle Of Attack increase

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-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1


Lo

cal C

olle

ctio

n E

ffic

ien

cy

AOA = 0º AOA = 4º AOA = 8º


Ice AccretionIce Accretion

Thermodynamic of Ice Accretion

Supercooled water droplet will freeze completely at impact to form ice on the impingement area or freeze partially to form ice on the impingement area and remaining water which runback outside of the impingement area.




Rime ice form when all water freeze at impactRime ice is associated to

• colder temperature, below -10°C• lower Liquid Water Content• smaller Median Volumetric Diameter

Iced zone is small and close to the leading edge and quite closely takes the original contour




Glaze ice form when a fraction of the water freeze at impactGlaze ice is associated to

• warmer temperature, above -10°C• high Liquid Water Content• greater Median Volumetric Diameter

Iced zone is large and tend to deform the aerodynamic profile due to horns formation




The capacity of ambient environment to absorb the latent heat of solidification while determine if rime or glaze ice is formed




Surface Temperature and Freezing Fraction

If the resulting surface temperature is above freezing, only a fraction of the impinging water is solidified at impact. The freezing fraction is calculated assuming a surface temperature equal to freezing.

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Ice Mass

subevapimpice mfmmm

Ice Thickness

ice

iceice

me




Ice Shapes predict with CIRALIMA 2D

-0.100

-0.075

-0.050

-0.025

0.000

0.025

0.050

0.075

0.100

-0.075 -0.050 -0.025 0.000 0.025 0.050 0.075 0.100 0.125 0.150 0.175

-28.3ºC -13.3ºC -7.8ºC -4.4ºC


Wind turbine icing simulated in icing wind tunnel at AMIL

LWC = 0.24 g/m³Temperature = -5.7°CAir speed = 4.2 m/sWind Turbine Speed = 16 RPMWind Turbine Diameter = 80 mTime = 4.5 hours


Wind Turbine



Wind Turbine

Aerodynamic Degradation

s

s

solds

news

T

TfTf

TT

Lift decreased from the hub to the tip.

Drag increased from the hub to the tip and was more affected than lift.

Ice impact on drag and lift was more significant after 20 m.

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0 5 10 15 20 25 30 35 40 45

r(m)

Lift

Co

eff

icie

nt

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0.05

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0.25

0.3

Dra

g C

oe

ffic

ien

t

Lift Coefficient Clean Airfoil Lift Coefficient Iced AirfoilDrag Coefficient Clean Airfoil Drag Coefficient Iced Airfoil


Ice Protection SystemIce Protection System

Type used with wind turbineElectro-thermal Hot airflowMicrowaves Icephobic coating

MethodAnti-icing: no ice is allowed to form Deicing: allow small ice thickness to form

before the deicing sequence is activated

s

s

solds

news

T

TfTf

TT



Advice•Protect the collected area, about 14% of the chord with AOA of 6º

•Maintain blade temperature below 50ºC to reduce the blade delamination risks

•Do not protect the first third part of the blade•Split blade into individual areas and controlled individually in power to reduce energy consumption



Advice• 3.5 more power to de/anti-ice the leading

edge at the tip compared to the hub• 1.5 more power to de/anti-ice the lower

surface then the upper surface



Anti-icing• Maintain the surface blade temperature

above freezing • With thermal system about 10 W/in² at the

tip• Electro-thermal, hot airflow or microwaves

-0.04

-0.02

0

0.02

0.04

-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22

(m)

(m)

without heatingwith heating

About 5 times more energy is needed in evaporative mode



Deicing• Less expensive than anti-icing and

minimizes runback water and refreezing water on unheated areas

• The allowed accreted ice is not sufficient to lead to significant aerodynamic penalties or to become a hazard

• With mechanical system about 2 W/in²/ice millimetre Ice thickness is not uniform

Ice detector for each blade area


ConclusionsConclusions

• Icing is a problem in cold climate for wind turbine due to freezing rain and drizzle, freezing fog at ground level or icing clouds when installed in altitude or frost when installed near water bodies.

• Ice accretion lead to aerodynamic penalties and decrease output power.

• Impact of glaze, rime or frost is difficult to quantify without more experimental and numerical simulations due to lack of data and knowledge.

• Existing ice protection systems are not adapted to wind turbine, low energy ice protection systems should be developed.



• Moreover, anti-icing systems are efficient when high frequency of icing event is expected or security is the most important factor.

• Dei-icing is more efficient than anti-icing , but is difficult to implement and more expensive.

• To reduce ice protection system power consumption • Optimize power in function of the wind turbine

rotating speed.• Protect the 2/3 extremity parts of the blade only



Question?

Documents

47th Aerospace Science Meeting and Exhibit, Orlando, Florida, 20091 47 th AIAA Aerospace Science Meeting and Exhibit Orlando, Florida, 5-8 January 2009