Wind Turbines in Cold Climate: Fluid Mechanics, Ice Accretion and Terrain EffectsM Ronnfors, R-Z Szasz, J Revstedt, Lund University

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

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=

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

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

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

Method 1 In-house code

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

Change the surface shape

• Every n:th time step– Can be extrapolated in time:

Vice= Vice* time– Trapped air can be accounted for

Ice shapes

Velocity fluctuationsRough iceClean airfoil Smooth ice

3◦

9◦

Comparing ice shapes, 3∘, method 1 and 2

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

Vortical structures (λ2)

Long structure

Small vortices

Acoustic sources

RMS Lighthill source

•Larger amplitude sources on pressure side

Acoustic density fluctuations

Acoustic presssure spectra

Some tones damped by ice

Acoustic presssure spectra

Continued work•Other icing conditions

–Add heat transfer•Acoustics

–Account for monopoles and dipoles as well

•Single and multiple turbines•Landscape/ground effects

Acknowledgements

• Financing: Energimyndigheten

• Computational resource: SNIC, Lunarc, Lund University