DSD-INT 2014 - Symposium Next Generation Hydro Software (NGHS) - (More) mesoscale horizontal flow-field modelling at a channel-river-junction, Regina Patzwahl, Federal Waterways Engineering and Research Institute (BAW)

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

Hydraulic Engineering · W2 · R. Patzwahl, F. Platzek, J.A. Jankowski · 5th november 2014
•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?
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
•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
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 data density in lab. Meas.

Time averaged computed flow field
Low data density 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

Sheet pile wall in scaled model
What is the influence of the sheet pile wall (rough!) on the flow field?
Location of detachment

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
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
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“

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 flow-field modelling at a channel-river-junction, Regina Patzwahl, Federal Waterways Engineering and Research Institute (BAW)

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DSD-INT 2014 - Symposium Next Generation Hydro Software (NGHS) - (More) mesoscale horizontal flow-field modelling at a channel-river-junction, Regina Patzwahl, Federal Waterways Engineering and Research Institute (BAW)