nexmex02072010 presentation rethore

8/8/2019 NEXMEX02072010 Presentation Rethore

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Modelling the MEXICO Wind Tunnel with CFD

Pierre-Elouan Rthor Niels N. Srensen Helge A. [email protected] [email protected] [email protected]

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

1 of 26 Rthor et al.Ris [email protected]

MEXICO Wind Tunnel CFD Model 1-2/7/10


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Introduction

Outline

1 IntroductionBackground

The tunnel








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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








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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.

8 of 26 Rthor et al.Ris DTU [email protected] Wind Tunnel CFD Model 1-2/7/10


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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.


M hi


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MeshingMesh design

Collector details

This part could have been so much more elegant with anunstructured flow solver!


M hi


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MeshingMesh design

On the meaning of life while meshing


M hi


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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








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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.


E l l


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Early results

Outline

1 Introduction







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.


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.


Early results


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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.


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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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[]


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

[]




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.


Early results


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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/Uin[]


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


Early results
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ySteady state k-



Early results
http://goback/


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ySteady state k-


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[]




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

[]




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.



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.

19 of 26Rthor et al.Ris DTU

[email protected] Wind Tunnel CFD Model 1-2/7/10

Early results


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Steady state k-

Axial velocity along cross sections

The upstream profiles look the same.



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-


The profiles start to change around 1.4D1.5D.



2 1 0 1 20.2

0

0.2

0.4

0.6

0.8

1

1.2


Uvelocity

U/U

in

[]


Tunnel & Disc

Tunnel & No disc

No tunnel & Disc


Early resultsSt d t t k


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Steady state k-


the central part of the wake is more detailed in the wind tunnelmesh than in the no wind tunnel mesh.



2 1 0 1 20.2

0

0.2

0.4

0.6

0.8

1

1.2


Uvelocity

U/U

in

[]


Tunnel & Disc

Tunnel & No disc

No tunnel & 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








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!).


[email protected]


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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Rthor et al.

Ris DTU

[email protected]


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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Rthor et al.

Ris DTU

[email protected]


Questions & Suggestions


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Thank you for your attention!

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Rthor et al.

Ris DTU

[email protected]


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