Download - Wind Turbine Icing- Challenges & Progress
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
e) Ice Detection
• In-direct method
– Production Data
• Direct Methods
– Sensors on the nacelle
– Sensors on the blade
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.
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
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…..!!!