DSD-INT 2014 - Symposium Next Generation Hydro Software (NGHS) - (More) mesoscale horizontal...

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Mesoscale horizontal flow-field modelling at

a channel-river-junction

Frank Platzek, Regina Patzwahl, Herman Kernkamp, Sander van der Pijl,

Jacek Jankowski, Boris Glander, Leo Stadler, Bernd Hentschel, Jan Becker

www.baw.de

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Mesoscale horizontal flow-field modelling at

a channel-river-junction

Bereich für das Einfügen von Bildern über den Menüpunkt Einfügen: Grafik

Dieses Textfeld bitte löschen! Frank Platzek, Regina Patzwahl, Herman Kernkamp, Sander van der Pijl,

Jacek Jankowski, Boris Glander, Leo Stadler, Bernd Hentschel, Jan Becker

Mesoscale horizontal flow-field modelling at a channel-river-junction

Mesoscale horizontal flow-field modelling at a channel-river-junction Hydraulic Engineering · W2 · R. Patzwahl, F. Platzek, J.A. Jankowski · 5th november 2014

OUTLINE

• Geometrical setting

• Field measurements

• Scale model

• Numerical model

• grid,

• boundary conditions,

• numerical settings,

• results

• Conclusions

Mesoscale horizontal flow-field modelling at a channel-river-junction


• Geometrical setting

• Field measurements

• Scale model

• Numerical model

• Conclusions 2013

• Channel mouth re-design

• Results

• Sheet pile wall modelling for beginners

OUTLINE


GEOMETRICAL SETTING


GEOMETRICAL SETTING

Topography in computational model

Dredged fairway

Groyne

Dunes

(depth 3 – 6 m)

Sheet pile walls


MEASURED DATA

Measured flow field

• Size of eddy is discharge independent

• Flow velocities increase with discharge

950 m³/s 1700 m³/s

1950 m³/s 840 m³/s


SCALE MODEL

4 km of river stretch = 67 m of model length

Length Scaling: 1:60

Height Scaling: 1:30

Stationary discharge conditions, non-movable gravel bed


SCALE MODEL

Measured flow field (surface velocities, 2D particle tracking)


NUMERICAL MODEL

• 11 km long river model

• Grid types:

• Quadrilateral (dx=2m),

river axis aligned,

# of elements: ~ 800.000

• Triangular (dx=1,5m),

# of elements: ~ 2.500 000

• Discharge at inflow: 986 m³/s

• Water level at outflow: 4.71 m

• Advection scheme:

Upwind Perot (2 types)

• Range of horizontal viscosities

• Smagorinsky off/ on


CONCLUSION 2013

The modelled flow field in the junction domain is sensitive to:

Advection scheme

Constant viscosity

Grid type

„Smagorinsky“

Lower velocities in

the eddy field

Numerical diffusion

„physically correct“?

Arguably improved?

Grid-dependent

results

Advection scheme

= crucial choice!

Grid-dependent

results


CONCLUSION 2013

The modelled eddy system in the recirculation zone is well represented in

• position,

• size,

• flow velocities

Best modelling result Scale model

1.0*10-6, Perot 3, Smag Field measurement


CONCLUSION 2013

Best modelling result

• Excellent validation case for modelling mesoscale horizontal recirculation

• Unique combined set of field data, scale model and numerical model data

Scale model

Field measurement


CONCLUSION 2013

• Excellent validation case for modelling mesoscale horizontal recirculation

• Unique combined set of field data, scale model and numerical model data

=> We follow the project with the new D-Flow FM engine of Delft3D Flexible

Mesh for studying purposes

Best modelling result

Scale model

Field measurement


CHANNEL MOUTH RE-DESIGN

…and we follow.

BAW-project continues with geometry studies accompagnied by Telemac2D-model

and the scaled model…

?

Sedimentation wedge

removed



Sedimentation wedge in

the up-stream part of the

mouth

Sedimentation wedge

removed

BAW-project continues with geometry studies accompagnied by Telemac2D-model

and the scaled model…



Result for final step

Low

da

ta d

ensity

in lab.

Meas.



Time averaged computed flow field

Low

da

ta d

ensity

in lab.

Meas.



• „Best result“ model settings deliver good results for geometry

variation

• Time dependent processes need to be taken into account

Lab. Meas. 2D-PTV Time averaged Result for final step



• „Best result“ model settings deliver good results for geometry

variation

• Time dependent processes need to be taken into account

Singular time step Lab. Meas. 2D-PTV Time averaged

So far, so good!

BUT:

Do we have the right results for the

right reasons?


SHEET PILE WALL MODELLING FOR BEGINNERS

Do these sheet pile walls have any influence on

the flow field?



Photo-grammetric measurement of topography in scaled model Sheet pile wall in scaled model



Photo-grammetric measurement of topography in scaled model Sheet pile wall in scaled model

What is the influence of the sheet pile wall

(rough!) on the flow field?

Location of

detachment



Photo-grammetric measurement of topography in scaled model

Experiment: Flat/ smooth wall instead of sheet pile wall



Results from scale model - 2D-PTV



• Higher velocities on the west side

• Extends more into the mouth



• Higher velocities on the west side

• Extends more into the mouth

Detachment of the flow triggered by

wall roughness!


RESULTS – Influence of grid type for advection scheme “Perot 3” – quads vs. triangles

Triangles

Quads

Reference data set

1.0*10-4

1.0*10-4

0 1.0*10-4

0 1.0*10-4


RESULTS – Influence of grid type for advection scheme “Perot 3” – quads vs. triangles

Triangles

Quads

Reference data set

1.0*10-4

1.0*10-4

0 1.0*10-4

0 1.0*10-4

? 1 + 1 = ?


Less grid-induced wall-friction with

triangular grid leads to good

agreement with smooth wall case

Accidently very good agreement with

roughness of sheet pile wall in

nature due to grid design

Scaled Model Scaled Model Delft3D FM Delft3D FM




Grid structure combined with

topography may provide you with

„numerical physics“!

First

lesson

learned



Conveyance approach

set to „3“



Conveyance approach

set to „0“

Conveyance approach

set to „3“



Seemingly harmless and well-

meant model settings – applied

outside the foreseen range of

applicability - may cause

unexpected effects !!

Second

lesson

Learned


THE END

Thank you for your attention

DSD-INT 2014 - Symposium Next Generation Hydro Software (NGHS) - (More) mesoscale horizontal...

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Transcript of DSD-INT 2014 - Symposium Next Generation Hydro Software (NGHS) - (More) mesoscale horizontal...