Transcript

Wind Turbine Icing-

Challenges & Progress

Muhammad S. Virk

Institute of Industrial Technology

Faculty of Engineering Science & Technology

(WindCoE Project Perspective)

Introduction

Cold regions have good resources of wind energy, but atmospheric icing is one of themajor hinderence in proper utilization of these useful resources.

Wind turbine operations/performance in cold regions get effected due to accreted ice thatleads to disrupted aerodynamics, increased fatigue and structural failure due to massimbalance and damage or harm caused by the possible uncontrolled shedding of icechunks from wind turbines.

Atmospheric icing on wind turbines mainly occurs due to collision and freezing of supercooled water droplets with the exposed surface of wind turbines. There is at present a needto develop a better understanding of atmopsheric icing physics and it’s resultant effects toimprove the design and safety of wind turbines operations in cold regions.

Ice accretion on wind tubines has resulted in up to 17% loss in annual energy production(AEP) and can reduce wind turbine performance in the range of 20-50%

International Energy Agency (IEA) Annex XIX: ‘Wind energy in cold climates’, also callsfor developing new methods to better predict the effects of ice accretion on energyproduction.

(Example of atmospheric ice accretion on wind turbines in cold regions)

[1]-Maissan, T.M., The Effects of the Black Blades on Surface Temperatures for Wind Turbines ,in W.A.T. J., Editor 2001, Université du Québec à Rimouski: Canada.

[2]- http://www.eolos.umn.edu/research.

Icing Effects on Wind Turbines

Main effects of atmospheric ice accretion on wind turbine are:

– Disrupted blade aerodynamics.

– Increased fatigue due to mass imbalance.

– Human’s harm due to ice shedding.

– Instrumental measurement errors.

– Loss of power production.

– Complete stop of power production.

Active anti icing and de-icing systems are installed on wind turbines to

minimize these effects.

– This complicates the design and increases the cost.

Wind Turbine Ice Accretion Physics

Rate and shape of atmospheric ice accretion on wind turbines depends uponboth geometric and atmospheric parameters, such as:

Location. Geometric dimensions. Surface material. Wind velocity. Atmospheric temperature. Droplet size (MVD). Liquid water content (LWC).

Methodologies

Extant of ice accretion can be estimated either by field measurements, lab

based experimentation or numerical methods with certain accuracy, because:

Computational fluid dynamics

Lab based tunnel testing (Wind tunnel or icing tunnel)

Field testing

Increasing

Cost

Wind Turbine Icing- Challenges

a) Disrupted Blade Aerodynamics

Dry Ice Wet Ice

b) Structural Inegrity/ Ice loads

c) Enhanced Noise Propogation

d) Ice Chunks

e) Ice Detection

• In-direct method

– Production Data

• Direct Methods

– Sensors on the nacelle

– Sensors on the blade

f) Ice Mitigation

De-icing using thermal appraoch

Anti icing using surface coatings

Wind CoE Progress

SCADA Data Analysis-

Icing Events Assesment

Wind Power

Icing Classsification

Assuming conditions: temperature below 0 0C; wind

velocity more than 20m/s, as well as the power

production between 600–2200 kW.

Figure shows that during three years (2013- 2015) icing events occurred 8, 9

and 11 days respectively.

Air Flow Behavior

Droplet Collision Efficiency

(Droplet Collision Efficiency along LE)

Ice Accretion

23

(Ice Growth along LE)

Air Flow Behavior

25

Droplet Behavior

26

27

Ice Accretion

28 / 30

-28%

Power curves

Ice Accretion on Wind Turbines

Analytical Modelling

The k-factor: Background

Assumes that ice accretion on reference collector is directly correlated with ice

accretion on the blade.

The k-factor is constant and is equal to 20, meaning that wind turbine blade will

accumulate 20 times as much ice as the collector.

Represents ice accretion at 85% blade length.

Reference collector is a cylinder, 30 mm in diameter and 0.5 meter length.

Reference collector is typically mounted on the on-site met mast.

The k-factor: Inertia parameter

Inertia parameter depends on the number of factors.

The main factor is the characteristic length of the object.

For cylinder, the characteristic length is the diameter, and for airfoil it is

twice the leading edge radius.

If these two are equal, their inertia parameter are equal, assuming they

are both subjected to the same icing conditions.

By extension, their collision efficiency should also be equal.

The k-factor: Assumptions

• Assumes that ice accretion on the collector and the blade can be

represented by a constant scaling factor.

• Assumes that ice accretion of the 85% of the span is representative of

the entire blade.

• Assumes that α1 = α2 = 1 for the wind turbine blade due to high true air

speed.

• Depends only on MVD, temperature, icing duration and LWC.

Case Study: Operating conditions

Parameter Value

Cylinder diameter (mm) 30

Air velocity (m/s) 7 (cylinder), 60 (airfoil)

Air temperature (°C) –5

Altitude (m.a.s.l.) 10

MVD (µm) 20

Liquid Water Content (g/m3) 0.4

Icing duration (min) 30

Airfoil types NACA 0012, NACA 0015

Chord length (m) 1.2 (NACA 0012), 1 (NACA 0015)

Droplet distribution Monodisperse, Langmuir D

Case study: CFD results comparison

Airfoil

(NACA)

Droplet

distribution

CFD simulations

Cylinder ice

accretion (g)

Airfoil ice

accretion (g)

Cylinder

collision

efficiency

Airfoil

collision

efficiency

k

0012Mono 22.067 753.222 0.1460 0.5812 34.13

Lang D 26.803 818.260 0.1773 0.6314 30.53

0015Mono 22.067 797.081 0.1460 0.6150 36.12

Lang D 26.803 877.076 0.1773 0.6768 32.72

Ice Detection

Lab Based Testing

Ev al. °C

-12.6

-10.4

-8.2

-6.0

-3.8

-1.6

0.6

2.8

LOI4

LOI3

LOI2

LOI1LOI0

Icing Station Installation

Remarks

Power losses due to icing on wind turbines occur not because of singlereason, but through a combination of effects that may not have beenthought carefully during wind park design process.

For icing on wind turbines ,’knowing something about behaviour of icing envelopes, even if there are errors around its fringes is better than not

knowing anything’.

Still Lots More To Learn…..!!!

This research work is funded by the WindCoE (Nordic Wind Energy Centre) project, funded within Interreg IVA Botnia-Atlantica, as part of European

Territorial Cooperation (ETC).

Thank You!


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