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[mesh manipulation] MergedMesh StitchMesh Tool

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Old   July 9, 2019, 12:31
Default MergedMesh StitchMesh Tool
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mohammad ja
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Hi dear friends
Hopefully you are doing well.
As a matter of fact, I generated a mesh with mergeMeshes and stitchmesh tools and I used Integral mode to couple the corresponding patches.
The masterMesh was generated by blockMesh with around 7 million cells and the slaveMesh was generated by snappyHexMesh with around 6 million cells as the geometry of slaveMesh was complex and also the enough layers were not generated in the boundary layer, (I played with parameters but unfortunately only a few layers is generated by snappyHexMesh tool and this is the reason that I decided to get the best features of both blockMesh and snappyHexMesh by mergeMesh and stitchmesh tools. In addition, because the cell is refined in all directions then the number of cells greatly is increased in case of mesh generation by snappyHexMesh tool.
The size of start cell on the wall is .04 mm in both x and y directions, for mastermesh the size of cell in span wise direction is .8 mm.
The slaveMesh contains a cavity and 3 orifices with 1.2 mm orifice diameter which is embedded in the second quarter of semi-cylinder part of the masterMesh.
When I stitch corresponding patches, some patches with a few faces are remained in the boundary while ideally the number of faces should be zero.
Because I did not know how to get rid of them then I simply defined the boundary condition on these patches as all of them are in between main patches with zeroGradient boundary condition. Then I defined the zeroGradient boundary condition for these patches.
The average and maximum non orthogonality of the generated mesh is 9 and 43 degrees with skewness of 3.7 and maximum and aspect ratio of 373.
After running the code, the required time for first iteration with HPC is 5 minutes and both iteration time and courant number continuously are decreased as well as the residuals.Now it is being run with 18 seconds per iteration.
Now I see the velocity changes is very slow in the boundary layer and and the recirculation region behind the cylinder is not formed yet after 0.44 s while I ran this case without embedded mesh (in case we only have a cylinder ) and that re circulation region nicely was formed after 0.2s and it is in good agreement with experiment.
I am worried that maybe the solver is not ok with this mergedmesh and this manipulation? I use pisoFoam solver. However, this re circulation region was formed in another mergedmesh case with less cells in the boundary layer but the flow was not stable.
In previous mesh I had 44 cells from y=0 (on the surface) to y= 44 mm, while in this case I have 108 cells in this distance and it is quite dense.
If non zero faces can create problem? of course I checked all of the on paraview and as I mentioned all of them are between main patches and their boundary conditions are zeroGradient.
The maximum courant number was stated from 11 and not it is 4 with average courant number of 0.07.
The attached pictures show the geometry and the embedded mesh in x-y plane.
It is appreciated if you have any advice.
Thanks
Mohammad
Attached Images
File Type: png mesh.png (33.6 KB, 4 views)
File Type: png mesh2.png (67.4 KB, 4 views)
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