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Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
OpenFOAM for CFD in water power
and for international collaboration
ASSOCIATE PROFESSOR HAKAN NILSSON
Outline of the presentation:
• OpenFOAM for CFD in water power
- Overview of flow in Hydro Power Stations
- OpenFOAM results from inlet to outlet and generator
(real geometries and academic test-cases)
- Validation against measurements
- Comparisons with results from CFX-5/10 and Fluent
• OpenFOAM for international collaboration
- The OpenFOAM Turbomachinery Working Group
- The OpenFOAM Wiki
- The OpenFOAM-extend project at SourceForge
- The OpenFOAM Workshop / Working Group Day
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Overview of Fluid Dynamics in Hydro Power Stations�����
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Axial diffusor
Static head
Pressure conduitTurbine
GeneratorShaft
Draft tube
Power distribution
Headwater
Tailwater
Source: Wikipedia
Some important flow features:
(Red text discussed more later)
• Intake losses – vortices, wakes, friction
• Pressure conduit – friction, secondary
flow, pressure transients
• Wicket gate and runner – separation,
wakes, clearance flow, cavitation,
secondary flow, rotor-stator interaction
• Draft tube and outlet – separation,
unsteadiness, secondary flow
• Bearings – friction, cavitation, dynamics
• Generator – convective cooling, friction
• Spillways – erosion of dams and river
• Fish friendliness – guide the fish to safe
passages
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Kaplan and Francis runners – the most common types in Sweden
Pressure conduit
Spiral casing Shaft
Axial diffusor
Shroud
Stay vanesGuide vanes
RunnerHub
Runner blade
Pressure conduit
Shaft Spiral casing
Runner
Axial diffusor
Stay vanes
Guide vanes
Shroud
Band
Crown
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Pressure conduit – Secondary flow
Olivier Petit, under my supervision
Here: the inlet pipe, spiral casing and distributor.
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
U9 spiral casing, OpenFOAM vs. CFX-10
We will have a look at results along the ’outlet line’:
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
U9 spiral casing, OpenFOAM vs. CFX-10
Velocity magnitude (left) and static pressure (right) at the ’outlet line’
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Wicket gate and runner – Rotor-stator interaction
Simulations by Hakan Nilsson & Martin Karlsson, LTU
Axi-symmetric
Guide vanes
Spiral casing
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Wicket gate and runner – Clearances
Kaplan runner tip and hub clearances
Simulations by Hakan Nilsson
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Runner – Validation of OpenFOAM in the Holleforsen runner
(velocity profiles at cross-sections Ia and Ib)
Z
R
Above the blade
Section Ia
Section Ib
0 0.2 0.4 0.6 0.8 10
0.5
1
1.5
2
Hub (0) to shroud (1), Ia
c v
0 0.2 0.4 0.6 0.8 10
0.5
1
1.5
2
Hub (0) to shroud (1), Ia
c v
0 0.2 0.4 0.6 0.8 1−0.5
0
0.5
1
1.5
Hub (0) to shroud (1), Ib
c v
Squares: measured axial velocity. Triangles: measured tangential velocity. In (a) the colors
correspond to two different measurements. In (b) and (c): Blue curve: quasi-steady draft tube,
Black curve: runner without hub clearance, Red curve: runner with hub clearance.
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Wicket gate and runner – CavitationCavitation occurs where the static pressure is low,
and when the static pressure increases the
cavitation implodes, causing erosion
(Collaboration with Naval Architecture and
LTH - Aurelia Vallier, co-supervised by me)
Source: Mikael Grekula, Naval Architecture, Chalmers
Source: tripatlas.com/Water_turbine
Source: Tobias Huuva, Naval Architecture, Chalmers
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Cavitation movie, courtesy of Tobias Huuva
We will see a sheet cavity form, re-entrant jets breaking off a part of the sheet, hair-pin
vortices, and cavitation shedding. The snapshot shows the re-entrant jet breaking the cavity.
The blue iso-surface is γ = 0.5 and the gray iso-surface is at a constant vorticity.
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Draft tube – Validation in the Holleforsen draft tube
(development of engineering quantities in the flow direction)
Quasi-steady draft tube computation
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1 1.1
Ib II III IVa
OpenFOAM
Cpr
m[−
]
cfx-5
0 0.02 0.04 0.06 0.08
0.1 0.12 0.14 0.16 0.18
0.2
Ib II III IVa
OpenFOAMcfx-5
ζ[−
]
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 0.5 1 1.5 2 2.5 3 3.5 4
Distance [m]
elbowOpenFOAM
cfx-5experiments
c p
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Distance [m]
elbow
corner
OpenFOAMcfx-5
experiments
c p
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
The Dellenback Combustor (resembling a draft tube)
kOmegaSSTF = Filtered kOmegaSST
Developed by Dr. Walter Gyllenram
Upper limit to the modelled length scale:
∆f = α max{∣
∣
∣
~U∣
∣
∣δt, ∆1/3
}
, α = 3 (α > 1)
Static pressure iso-surfaces
kOmegaSST kOmegaSSTF – one revolution of the vortex rope
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Combustor velocity profilesCombustor velocity profiles of kOmegaSSTF (solid), kOmegaSST (dashed) and Fluent k−ω SST
(dashed-dotted). Markers from measurements.
D
rz
z/D =
0.25 0.50.75 1.02.0
3.04.0
0 0.2 0.4 0.6 0.8 1 1.2 1.40
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Vz
r/D
0.5 1 1.5 2 2.5 3 3.5 4 4.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Vz
r/D
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
r/D
z/D
Vθ
1 1.5 2 2.5 3 3.5 4 4.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
r/D
z/D
Vθ
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Generators – Convective cooling
Pirooz Moradnia, under my supervision
Some of the pictures from: http://www.el.angstrom.uu.se/frameset.html?/forskningsprojekt/vattenkraft.html
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Summary – special needs for CFD in Hydro Power Stations
• Rotating coordinate systems / multiple frames of reference
• Sliding grid / mixing plane / GGI
• Rotational periodic boundaries (conformal / non-conformal)
• Unsteady turbulence modeling in coarse grids and large time steps
• Wall treatment in coarse grids and unsteady flow
• High-order discretization schemes and automatic mesh refinement for
coarse and skew grids
• Cavitation, free surfaces / two phase methods
• Solvers that perform well in coarse and skew grids
• Fine resolution in large domains (parallel computations)
• Moving mesh (rotor dynamics)
• A cheap, powerful and accurate CFD tool for industry / academia,
research / development / teaching, and global collaborations – OpenFOAM
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
OpenFOAM for international collaboration
• This part is based on web pages:
- The OpenFOAM Wiki
http://openfoamwiki.net
- The OpenFOAM Turbomachinery Working Group
http://openfoamwiki.net/index.php/Sig_Turbomachiner y
- The OpenFOAM-extend project at SourceForge
http://openfoam-extend.wiki.sourceforge.net/
- The OpenFOAM Workshop / Working Group Day
http://www.openfoamworkshop.org
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
The ERCOFTAC Centrifugal Pump
The 2D mesh, impeller blade (blue, rotating) and diffuser blade (red, fixed) regions.
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
The ERCOFTAC Centrifugal Pump
These are ’frozen rotor’ results with MRFSimpleFoam and Ggi /stitchMesh (no difference)
MRF = Multiple Reference Frames
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
The ERCOFTAC Centrifugal Pump
These are ’sliding mesh’ results with turbDyMFoam and Ggi
Hakan Nilsson, Chalmers / Applied Mechanics / Fluid Dynamics
Thank you for your attention!
Learn more about OpenFOAM at the homepage of my course ’CFD with OpenSource Software’:
http://www.tfd.chalmers.se/˜hani/kurser/OS_CFD_2008 /Send me an e-mail if you want updates ([email protected] ).
Acknowledgements
Professor Hrvoje Jasak is greatly acknowledged.
Hakan Nilsson is partly financed by SVC (www.svc.nu):
Swedish Energy Agency, ELFORSK, Svenska Kraftnat, 1
Chalmers, LTU, KTH, UU1Companies involved: CarlBro, E.ON Vattenkraft Sverige, Fortum Generation, Jamtkraft, Jonkoping Energi, Malarenergi, Skelleftea Kraft, Sollefteaforsens,
Statoil Lubricants, Sweco VBB, Sweco Energuide, SweMin, Tekniska Verken i Linkoping, Vattenfall Research and Development, Vattenfall Vattenkraft, VG Power,
Oresundskraft, Waplans and Andritz Inepar Hydro