[Other] Mesh and simulation two unconnected pipes

pangasio · October 4, 2018, 06:56

Hi everyone!

Problem description: I want to simulate the airflow through two parallel and not connected "pipes" (both pipes are not smooth inside and have their own geometry). The airflow enters both pipes from one side and exists from the opposite side. I have 3 stl files for each pipe describing the pipe, the inlet and the outlet region.

I initially merged the stl from both files together, obtaining an stl file describing the two pipes, a single inlet and a single outlet file for both. I tried to use snappyHexMesh to create the mesh and simpleFoam for the simulation, but due to the parameter locationInMesh I can basically select only one of the two pipes on which run the simulation.

After reading online and on this forum I changed approach and meshed the two pipes independently and then merged them together using mergeMeshes. which creates a new polymesh that I then move in the constant folder. I work with multiprocessor but if I try to run simpleFoam the decomposePar returns the following error:

Code:

--> FOAM FATAL IO ERROR: 
Cannot find patchField entry for walls

file: /home/mpiuser/cloud/noseCFD/max/0054-middle/left/run/0/k.boundaryField from line 28 to line 41.

    From function void Foam::GeometricField<Type, PatchField, GeoMesh>::Boundary::readField(const Foam::DimensionedField<TypeR, GeoMesh>&, const Foam::dictionary&) [with Type = double; PatchField = Foam::fvPatchField; GeoMesh = Foam::volMesh]
     in file /home/ubuntu/OpenFOAM/OpenFOAM-5.x/src/OpenFOAM/lnInclude/GeometricBoundaryField.C at line 191.

Is my approach valid or did I make some errors? Is it the described simulation (single airflow going through two not connected and similar geometry) doable in OpenFOAM?

Thanks in advance for the help!

fra76 · October 5, 2018, 01:49

Hi,

In th recent versions of snappyHexMesh you can specify multiple inside points using locationsInMesh entry. In this way you should be able to obtain your disconnected mesh from the beginning. This is what you do with CHT problems, for example, where you have fluid and solid regions.
Merging two meshes should work as well. The error you re Perot seems, to me, more related to the setup (fields and boundary file) than to a problem with the mesh. checkMesh can help you in this.

My silly question however is another one. If the pipes are disconnected, why don’t you keep it simple and simulate them separately, merging the results at post processing?

Francesco

October 4, 2018, 06:56	Mesh and simulation two unconnected pipes	#1
pangasio New Member Join Date: Oct 2018 Posts: 1 Rep Power: 0	Hi everyone! Problem description: I want to simulate the airflow through two parallel and not connected "pipes" (both pipes are not smooth inside and have their own geometry). The airflow enters both pipes from one side and exists from the opposite side. I have 3 stl files for each pipe describing the pipe, the inlet and the outlet region. I initially merged the stl from both files together, obtaining an stl file describing the two pipes, a single inlet and a single outlet file for both. I tried to use snappyHexMesh to create the mesh and simpleFoam for the simulation, but due to the parameter locationInMesh I can basically select only one of the two pipes on which run the simulation. After reading online and on this forum I changed approach and meshed the two pipes independently and then merged them together using mergeMeshes. which creates a new polymesh that I then move in the constant folder. I work with multiprocessor but if I try to run simpleFoam the decomposePar returns the following error: Code: --> FOAM FATAL IO ERROR: Cannot find patchField entry for walls file: /home/mpiuser/cloud/noseCFD/max/0054-middle/left/run/0/k.boundaryField from line 28 to line 41. From function void Foam::GeometricField<Type, PatchField, GeoMesh>::Boundary::readField(const Foam::DimensionedField<TypeR, GeoMesh>&, const Foam::dictionary&) [with Type = double; PatchField = Foam::fvPatchField; GeoMesh = Foam::volMesh] in file /home/ubuntu/OpenFOAM/OpenFOAM-5.x/src/OpenFOAM/lnInclude/GeometricBoundaryField.C at line 191. Is my approach valid or did I make some errors? Is it the described simulation (single airflow going through two not connected and similar geometry) doable in OpenFOAM? Thanks in advance for the help!

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October 5, 2018, 01:49		#2
fra76 Senior Member Francesco Del Citto Join Date: Mar 2009 Location: Zürich Area, Switzerland Posts: 237 Rep Power: 18	Hi, In th recent versions of snappyHexMesh you can specify multiple inside points using locationsInMesh entry. In this way you should be able to obtain your disconnected mesh from the beginning. This is what you do with CHT problems, for example, where you have fluid and solid regions. Merging two meshes should work as well. The error you re Perot seems, to me, more related to the setup (fields and boundary file) than to a problem with the mesh. checkMesh can help you in this. My silly question however is another one. If the pipes are disconnected, why don’t you keep it simple and simulate them separately, merging the results at post processing? Francesco