Initial implementation of chtMultiRegionSimpleFoam, conjugate heat transfer support

[kevinsmia1939]

Add chtMultiRegionSimpleFoam solver to CfdOF with multi-region CHT support

There are several limitations at the moment.

• Only 1 fluid domain, so heat exchanger cannot be done yet.
• I tested only gmsh. cfmesh has not been test. snappyhexmesh have to support multi-body mesh.
• Turbulent RANS, kOmegaSST works, but I encounter stability issue half way into simulation with the example file I gave. We should create better file to test.
• Only aluminium properties at the moment, but can add more later.
• The fluid box and solids where heat is flowing though must be combine with "boolean fragments".

FreeCAD version 1.1.1 and openfoam2512 was tested.
Open the example I gave, write mesh case, run mesh, write case, and run case should start simulation without issue.
To view your result, open ParaView and add extractor block to see fluid or solid part, see screenshot.
Most of the codes are written with Claude code.

The next steps after this to put CHT in usable state includes,
Test different combinations and conditions
Test different cases with different wall boundary types, cyclic, symmetry, etc.
Add demo
Test with meanflowvelocity
Test different Turbulent model. A case without stability issues. Then add support for different Turbulent model.
Test different meshing.
Add more solid properties.

This PR still need much more testing until it is ready to merge. Will continue to update status.

All test pass except #262 which will need to merge first.

The example shown below is a heat sink with constant temperature on the bottom. Inlet and outlet flow over at 500mm/s.



cht_heatsink_test.FCStd.txt

[oliveroxtoby]

Thanks for taking this on.

One comment you could perhaps consider: My plan for this is to allow multiple mesh objects which would be connected via the non-conformal region-coupled boundaries in a similar way to how the periodic master/slave boundaries are currently implemented. This would be fairly general and not require us to implement a specialised method for each different mesher.

[kevinsmia1939]

[kevinsmia1939]

Initial support for steady-state conjugate heat transfer case
generation using OpenFOAM chtMultiRegionSimpleFoam solver.

New features

• Initial support for chtMultiRegionSimpleFoam solver
• Fluid and solid regions can be written as an OpenFOAM multi-region case
• Add solid region material properties (e.g. heat conductivity, heat generation)
• Fluid and solid thermophysical properties are written per region.
• Solid properties added. This PR is not required anymore Add solid thermal material cards #281 material properties have been included in this PR.
• Coupled temperature boundary conditions are created for fluid-solid and
  solid-solid interfaces produced by splitMeshRegions
• Solid heat sources can be written through fvOptions

  volumeMode      specific;
  injectionRateSuSp
  {
      h    (10000000.0 0);
  }

Mesh support

Only Gmsh-based meshing is supported for the initial CHT implementation.

The CHT workflow relies on gmsh volume/cell-zone output and on subsequent
OpenFOAM region splitting. Other CfdOF meshing backends are not covered by this
initial implementation and should be treated as unsupported for CHT cases.

Testing

I test the following combinations to evaluate the robustness of the CfdOF CHT implementation, all in laminar except one.

• Single fluid + single solid, no heat generation, fixed-temperature solid face.
• Single fluid + single solid, volumetric heat generation in solid.
• Single fluid + multiple solids, different materials.
• CHT + cyclic boundary.
• CHT + meanVelocityForce with SelectionMode = all.
• CHT + meanVelocityForce with SelectionMode = region.
• CHT with no solid heat generation, to confirm passive solids still solve.
• CHT + RANS turbulence model

Example case

simple_heat_fin.FCStd : This is the simplest setup of chtMultiRegionSimpleFoam. The case feature a rectagular fin with constant temperature heat source at the base.

microchip_cooling.FCStd : This example feature a setup akin to cooling microchip with fin heatsink with force convection from mean velocity force cell zone as a fan. This example features a microchip which generate volumetric heat. The other 3 solid regions include PCB with plastic material properties assigned, heat sink with aluminium material, fan case with plastic material. The convection was imposed with a mean velocity force cell zone on the top of the heat sink.

Laminar flow was used.
Boolean fragments was used to create regions.

Next steps

• Add support for connection via the non-conformal region-coupled boundaries.
• Add support for fluid multi-region, this will allow heat exchanger simulation.