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Modelling the MEXICO Wind Tunnel with CFD
Pierre-Elouan Rthor Niels N. Srensen Helge A. Madsenpire@risoe.dtu.dk nsqr@risoe.dtu.dk hama@risoe.dtu.dk
Wind Energy Division Ris DTU
MexNext Meeting
Forth Heraklion Crete 1-2/7/10
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Outline
1 IntroductionBackground
The tunnel
2 MeshingCAT fileMesh design
3 Actuator Disc Model
4 Early resultsConvergence issuesSteady state k-Unsteady DES
5 ConclusionSummaryFuture work
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Introduction
Outline
1 IntroductionBackground
The tunnel
2 MeshingCAT fileMesh design
3 Actuator Disc Model
4 Early resultsConvergence issuesSteady state k-Unsteady DES
5 ConclusionSummaryFuture work
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IntroductionBackground
Questions surrounding the tunnel effect
Does the recirculation region affects the wake measurements?
Does the wind turbine blockage effect affects the wind speed
measurements?Is the wind turbine affected by the wind tunnel?
How far downstream can we measure the wake?
Is there some unsteady effects?
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Spoiler:
I wont answer any ofthese questions!
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IntroductionThe tunnel
In Real Life
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Meshing
Outline
1 Introduction
BackgroundThe tunnel
2 MeshingCAT fileMesh design
3 Actuator Disc Model
4 Early resultsConvergence issuesSteady state k-Unsteady DES
5 ConclusionSummaryFuture work
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MeshingCAT file
Perspective view
The nozzle and collector shapes are not available (confidential).
We made up some streamlined designs.
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MeshingCAT file
Top & Side view
Neglected in the mesh:The two fundamentsWind turbine hubWind turbine towerWall roughnessThe small people waving
hands
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MeshingMesh design
Top & Side view
The inlet and outlet are extended to avoid boundary issues.
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MeshingMesh design
Perspective view
We use a slip boundary condition at the surface (zero gradient).This reduces dramatically the number of cells necessary, but it
is done at the expense of the boundary layer description.
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MeshingMesh design
Top view - Close up
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MeshingMesh design
Internal Meshing Concept
The flow solver we use EllipSys is a structured multiblockformulation. It is very fast to solve but makes complexgeometries difficult to mesh.
The collector was the most difficult part. Especially themodellisation of the hole and the lips.
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MeshingMesh design
Collector details
This part could have been so much more elegant with anunstructured flow solver!
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MeshingMesh design
On the meaning of life while meshing
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MeshingMesh design
On the meaning of life while meshing
Nietzsche
It is only as an aesthetic
phenomenon that life and existence
are eternally justified The Birth of Tragedy (1872)
=> Existence and the world becomemeaningful not as objects of knowledge butas artistic experience.
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Actuator Disc Model
Outline
1 Introduction
BackgroundThe tunnel
2 MeshingCAT fileMesh design
3 Actuator Disc Model
4 Early resultsConvergence issuesSteady state k-Unsteady DES
5 ConclusionSummaryFuture work
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Actuator Disc Model
Force Distribution
The forces can be obtained fromdifferent sources
MeasurementsBlade Element Method (BEM)Basic actuator disc theoryFull rotor computation in CFD
The force history of a rotor revolution is
smeared over a polar grid
The contribution of each polar gridelements is added proportionally to theintersectional area with thecomputational mesh
The final force can be used directly orscaled using the local velocity:
F = 12
ACD(U n)2
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Actuator Disc Model
Wake rotation
The tangential forces create the wake rotation (visible throughthe stream-ribbons twisting).
In the present results the force distribution are found from a fullrotor computation of a Nortank 500 kW turbine. They arenormalized with the inflow velocities and the thrust coefficient.
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Early results
Outline
1 Introduction
BackgroundThe tunnel
2 MeshingCAT fileMesh design
3 Actuator Disc Model
4 Early resultsConvergence issuesSteady state k-Unsteady DES
5 ConclusionSummaryFuture work
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Early results
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Early resultsConvergence issues
Residuals convergence
Resid
uals
log10
(|xi-1-
xi|/|x
i|)[-
]
Iterations [-]
The velocity and pressure residuals only converge to|xi xi1|/|xi| = 10
2 (we usually prefer |xi xi1|/|xi| < 106).
This can indicate a poor mesh design or physical instabilities.
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Early results
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Early resultsConvergence issues
Disc velocity convergence
Discv e
locity[m/s]
Iterations [-]
However, the velocity integrated over the disc reaches aconstant value.
This shows that the inflow velocity is relatively steady.
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Early resultsSteady state k-
Different wind speeds & same CT= 0.77
All the velocities collapse completely.CT is the only parameter.
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10 4.07 1.77 0 2.98 6.03 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline x/D []
Uvelocity
U/U
in
[]
Velocity centerline z/D=0.25
Disc u=1.0m/sDisc u=2.0m/s
Disc u=3.0m/s
Disc u=4.0m/s
Disc u=5.0m/s
Disc u=6.0m/s
Disc u=7.0m/s
Disc u=8.0m/s
Disc u=9.0m/s
Early results
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Early resultsSteady state k-
All cases with same loading (CT= 0.77)
10 4.07 1.77 0 2.98 6.03 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline x/D []
UvelocityU/Uin[]
Velocity centerline z/D=0.45
Tunnel & DiscTunnel & No disc
No tunnel & DiscTunnel (No Hole) & Disc
10 4.07 1.77 0 2.98 6.03 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline x/D []
Uvelocity
U/Uin
[]
Velocity centerline z/D=0.33
Tunnel & DiscTunnel & No disc
No tunnel & DiscTunnel (No Hole) & Disc
constant velocity in the jet section with no disc.
Increase bump in the nozzle.Relatively good agreement between the wind tunnel / no wind
tunnel case for x/ D [1, 1.3].
Little difference between hole / no hole cases for x/D > 1.3.
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Early resultsSteady state k-
All cases with same loading (CT= 0.77)
10 4.07 1.77 0 2.98 6.03 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline x/D []
Uvelocity
U/Uin[]
Velocity centerline z/D=0.45
Tunnel & DiscTunnel & No discNo tunnel & DiscTunnel (No Hole) & Disc
10 4.07 1.77 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline
UvelocityU/Uin
[]
Velocity cent
Tunnel & DiscTunnel & No discNo tunnel & DiscTunnel (No Hole) & Disc
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Early results
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ySteady state k-
All cases with same loading (CT= 0.77)
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Early results
http://goback/ -
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ySteady state k-
All cases with same loading (CT= 0.77)
10 4.07 1.77 0 2.98 6.03 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline x/D []
UvelocityU/Uin[]
Velocity centerline z/D=0.45
Tunnel & DiscTunnel & No disc
No tunnel & DiscTunnel (No Hole) & Disc
10 4.07 1.77 0 2.98 6.03 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Centerline x/D []
Uvelocity
U/Uin
[]
Velocity centerline z/D=0.33
Tunnel & DiscTunnel & No disc
No tunnel & DiscTunnel (No Hole) & Disc
constant velocity in the jet section with no disc.
Increase bump in the nozzle.Relatively good agreement between the wind tunnel / no wind
tunnel case for x/ D [1, 1.3].
Little difference between hole / no hole cases for x/D > 1.3.
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Early results
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ySteady state k-
Vorticity contour
Instability region at the jet interface.
Rapid contraction of the wake width due to the collector.
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Steady state k-
Axial velocity along cross sections
The upstream profiles look the same.
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2 1 0 1 20.2
0
0.2
0.4
0.6
0.8
1
1.2
Cross section z/D []
Uvelocity
U/U
in
[]
Velocity cross section x/D=1
Tunnel & Disc
Tunnel & No disc
No tunnel & Disc
Tunnel (No Hole) & Disc
Early resultsd k
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Steady state k-
Axial velocity along cross sections
The profiles start to change around 1.4D1.5D.
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2 1 0 1 20.2
0
0.2
0.4
0.6
0.8
1
1.2
Cross section z/D []
Uvelocity
U/U
in
[]
Velocity cross section x/D=1
Tunnel & Disc
Tunnel & No disc
No tunnel & Disc
Tunnel (No Hole) & Disc
Early resultsSt d t t k
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Steady state k-
Axial velocity along cross sections
the central part of the wake is more detailed in the wind tunnelmesh than in the no wind tunnel mesh.
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2 1 0 1 20.2
0
0.2
0.4
0.6
0.8
1
1.2
Cross section z/D []
Uvelocity
U/U
in
[]
Velocity cross section x/D=1
Tunnel & Disc
Tunnel & No disc
No tunnel & Disc
Tunnel (No Hole) & Disc
Early resultsU t d DES
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Unsteady DES
Axial velocity contour
Unsteady region at the jet interface.Recirculation.Wake oscillation.
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Conclusion
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Outline
1 Introduction
BackgroundThe tunnel
2 MeshingCAT fileMesh design
3 Actuator Disc Model
4 Early resultsConvergence issuesSteady state k-Unsteady DES
5 ConclusionSummaryFuture work
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ConclusionSummary
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Summary
What have we learned so far?
On meshing:
It would be nice to have the exact geometry of the nozzle.Meshing wind tunnel in block structured mesh can be very slowand painful.
Unstructured mesh can be a good idea.Reading Nietzsche helps (but consume it with moderation!).
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ConclusionSummary
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Summary
What have we learned so far?
On meshing:
It would be nice to have the exact geometry of the nozzle.Meshing wind tunnel in block structured mesh can be very slowand painful.
Unstructured mesh can be a good idea.Reading Nietzsche helps (but consume it with moderation!).
On open-jet wind tunnels:
It generates unsteady oscillations at the interface that impacts the
wake structure.The jet should be much wider than the turbine.The collector has a big impact on the wake region (x > 1.3D). It is
not clear yet if the wake measurements are compromised.The hole does not seem to have an important effect on the
recirculation.
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ConclusionFuture work
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Future work
What is next?
Full rotor computation (overset grid & parallel).
Linking the actuator disc with an aerodynamic code (e.g.HAWC2, FLEX5).
Actuator line.
Comparison with the measurements.
Refined Nozzle.
Modelling other bluff bodies (Hub, Tower, Fundaments, smallpeople waving hands)?
. . . Other ideas?
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Questions & Suggestions
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Thank you for your attention!
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