Turbulence modeling issue

[Ali Fauze]

Hello,

I’m working on a simulation of a 90° elbow circular pipe with turbulent water flow and encountering some issues. When comparing my results to Fluent and analytic estimations, the discrepancies are significant:
-the analytical estimation 470 Pa.
-Fluent results 550 Pa.
-OpenLB: Fluctuates between 1700 and 2500 Pa, averaging at 2190 Pa (the average is based on “the steady time” of the simulation)
Inlet BC used: density 997 kg/m3, and kinematic viscosity 8.927e-7 m2/s.
Additionally, i noticed unrealistic high pressure (up to 14000Pa) at some points at the inlet near the walls, which is unexpected given the symmetrical shape of the pipe (pressure value and the distribution are unexpected, they are distributed in a random asymmetric way).

Also, I took a look on the Venturi3D case where density was 1 Kg/m3 (possibly air at 80°C) and the kinematic viscosity was 0.001 m2/s which seems too high.

Can anyone clarify the fluid used in the Venturi3D case and suggest what might be causing the errors in my simulation?

Thanks for your help.
Best Regards.

[Adrian]

Can you share any details of your case setup? Without this it could be anything.

The fluid parameters in Venturi 3D are just as a model example and are not supposed to model an actual real world fluid.

[Ali Fauze]

Hello Adrian,

Thanks for your response, sure!
Fluid properties:
Density: 997 Kg/m3
Kinematic Viscosity 8.927e-7 m2/s
Inlet Velocity 1 m/s
Dynamics used –> SmagorinskyBGK
Resolution –> 25
DeltaX –> 0.004
deltaT –> 0.0004
Descriptor D3Q19
Inlet –> smooth start-up 1m/s velocity in (checked the velocity inlet in paraview) and InterpolatedVelocityBoundqry is used
Outlet –> InterpolatedPressureBoundqry is used

I am at your disposal for any further information.

Thanks for your help.
Best regards.

[Adrian]

Ok – while the parameters and model selection look ok I can still only guess without seeing the actual case and / or a more specific question.

e.g. your reference to “[…] at some points at the inlet near the walls” leads me to suspect that there is a problem in your geometry setup / discretization. It could also be caused by a mismatch between material geometry and your boundary setup. Or there may be an issue with how the framework is used (e.g. dynamics parameters not defined correctly, or…). Or it could be something else entirely.

[Ali Fauze]

Hello Adrian,

Thank you for the response,

The geometry and material definition I modified the existing Aorta3D model and then I verified if the materials are correctly set in Paraview, And the same for the discretization and also I refined my model but I does remarked any significant change. Maybe if I can share with you a screenShot of the inlet, it will give you an idea.

Thanks for your help.
Best regards.

[mathias]

It might be that you need a wall modell to correctly map the torbulent boundary layer.

[Author]

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