Heat and flow equations in Elmer problem

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mst31
Posts: 9
Joined: Sun Apr 03, 2022 10:43 pm

Heat and flow equations in Elmer problem

Post by mst31 »

Hello!
I try simulate natural convection in heat sink. For it I created project using heat and flow equtions in Elmer. The project consists of heat sink, transistors and air cube - picture is below.
1.png
1.png (68.85 KiB) Viewed 742 times
Heat equations is deleted for to debug flow equation. But Elmer prints warnings many times: "WARNING:: ListFind: Requested property: [Viscosity], not found" and solve is not converged. If I remove all solids then all works correctrly.
2.png
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How I understood, elements of solid is used in flow equation and matrix become unconditional. How can I do that Elmer doesn't take into account elements of solid in flow equation? Whether it is possible?

Code: Select all

OS: Linux Mint 20.3 (X-Cinnamon/cinnamon)
Word size of FreeCAD: 64-bit
Version: 0.20.
Build type: Release
Branch: unknown
Hash: cd53c06b9899b03fe88d2a2fe8258422e7ac9c09
Python 3.8.10, Qt 5.12.8, Coin 4.0.0, OCC 7.5.2
Locale: Russian/Russia (ru_RU)
thschrader
Veteran
Posts: 2581
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Heat and flow equations in Elmer problem

Post by thschrader »

Can you post your FreeCAD-file?
right-click on gmsh in model-tree, choose "Clear Mesh" to reduce file size.
mst31
Posts: 9
Joined: Sun Apr 03, 2022 10:43 pm

Re: Heat and flow equations in Elmer problem

Post by mst31 »

Here is project file:
https://drive.google.com/file/d/1SzFhba ... sp=sharing
I can not attach it so I upload to Google drive.
thschrader
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Posts: 2581
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Heat and flow equations in Elmer problem

Post by thschrader »

I can run your model, get the same viscosity error too. Solver runs and runs....
But in sif the viscosity is correct assigned to body 24, the fluid domain.
The mesh is far too rough, but when using a finer mesh (I played with snappyhexmesh from openfoam)
to fill the 3 mm gaps between the radiators, I get more than 3,6 mio cells. Even when using a 1/2 model.
Which makes your model very hard to debug...long runtime...
I am not very familiar with Elmer multiphysics, so I will try to make an openfoam calculation with cfdof-wb.
Lets see how this works...
Regards Thomas
meshes.JPG
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mst31
Posts: 9
Joined: Sun Apr 03, 2022 10:43 pm

Re: Heat and flow equations in Elmer problem

Post by mst31 »

Thank you for answer!
Does cfdof-wb support heat transfer with flow?
I also try to set manually in generated sif-file viscosity equal 0 for all solid materials. Now solve is converged.
thschrader
Veteran
Posts: 2581
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Heat and flow equations in Elmer problem

Post by thschrader »

See features of cfdof-workbench here:
https://github.com/jaheyns/CfdOF

If you are interested in CFD, you should give it a try :mrgreen:
thschrader
Veteran
Posts: 2581
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Heat and flow equations in Elmer problem

Post by thschrader »

Quick and dirty with cfdof-workbench, solver buoyantPimpleFoam.
Done with
bluecfd 2020-1
https://bluecfd.github.io/Core/Downloads/
and
OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.27428 (Git)
Build type: Release
Branch: master
Hash: 27460358508a2057e0ec57a418641435f12628dd
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.3
Locale: German/Germany (de_DE)
cigarette.FCStd
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mst31
Posts: 9
Joined: Sun Apr 03, 2022 10:43 pm

Re: Heat and flow equations in Elmer problem

Post by mst31 »

Thank you for example! I'm impressed by this, I will try this workbench)
mst31
Posts: 9
Joined: Sun Apr 03, 2022 10:43 pm

Re: Heat and flow equations in Elmer problem

Post by mst31 »

As for the problem. I solved it. In generated sif-file should be removed Navie-Stokes equation from Solid equations.
Before:

Code: Select all

Equation 1
  Active Solvers(3) = Integer 2 1 3
  Convection = String "Computed"
End
After:

Code: Select all

Equation 1
  Active Solvers(2) = Integer 2 3
  Convection = String "Computed"
End
where Navie-Stokes solver has number 1.
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