wind turbines in cold climate: fluid mechanics, ice
TRANSCRIPT
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Wind Turbines in Cold Climate: Fluid Mechanics, Ice Accretion and Terrain EffectsM Ronnfors, R-Z Szasz, J Revstedt, Lund University
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Work packages
•WP1: Detailed simulations of ice accretionon a single blade•WP2: Studies of how the acoustic sourcesare affected by ice accretion•WP3: Studies of terrain effects•WP4: Studies of noise generation from several turbines
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Goals•Develop tool to model simultaneously flow and ice accretion
–Efficient (relative)–Flexible
»Avoid/fewer model coefficients»Complex/moving geometries
–Combine with other modules»Performance»Noise
uAdt
dM φααα 321=
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Wind turbine blades vs. aircraft wings
• Programs for ice accretion on aircraft wings– Not optimal for wind turbines
• Differences in – Incompressible vs compressible– Subsonic vs supersonic– High AOA vs low AOA– Small chords vs big chords
• Need better tools to predict ice on wind turbine blades
Source: pixabay.com
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Methods ice accretion
• 1. In-house code– LPT (Lagrangian Particle tracking)– LES (Large Eddy Simulation)– Immersed Boundary Method
» Move surface with source terms, same mesh• 2. OpenFoam (OpenSource, free CFD software)
– Makkonen (Euler-Euler approach)– LPT (Lagrangian Particle tracking)– LES (Large Eddy Simulation)– Dynamic mesh
» Move mesh with surface
• Compare programs and models
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Methods ice accretion
• Method 2 OpenFoam– Incompressible N-S– LES– FVM (2:nd order)
» Slower– Hexahedral grid
» Refined around the wing
• Method 1 In-house code– Incompressible N-S– LES– Finite differences (3:rd, 4:th)
» Faster– Equidistant cartesian grid
» No refinement around wing
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Method 1 In-house code
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Set-upParameter Value
Profile NACA 63415
Angle of attack 3∘, 9∘
LWC 0.37 g/m3
MVD 27.6 μm
Vrel 18.7 m/s
Re 2.49e5
Time 10.6 min
Mass of ice 24 g
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Change the surface shape
• Every n:th time step– Can be extrapolated in time:
Vice= Vice* time– Trapped air can be accounted for
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Ice shapes
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Velocity fluctuationsRough iceClean airfoil Smooth ice
3◦
9◦
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Comparing ice shapes, 3∘, method 1 and 2
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Noise computations
•Hybrid-method (Lighthill)
•Advantages–Dedicated solvers for flow & acoustics–Acoustic sources can be iterated–Possibility of different
»Mesh»Computed physical time
ji
ij
xxT
ptp
c ∂∂
∂=∇−
∂∂ 2
22
2
2 ''1
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Vortical structures (λ2)
Long structure
Small vortices
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Acoustic sources
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RMS Lighthill source
•Larger amplitude sources on pressure side
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Acoustic density fluctuations
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Acoustic presssure spectra
Some tones damped by ice
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Acoustic presssure spectra
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Continued work•Other icing conditions
–Add heat transfer•Acoustics
–Account for monopoles and dipoles as well
•Single and multiple turbines•Landscape/ground effects
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Acknowledgements
• Financing: Energimyndigheten
• Computational resource: SNIC, Lunarc, Lund University
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