Star CCM+ CHT surface mesh problems.. intersections wont go away.

lelandt50 · June 16, 2022, 16:08

I've been trying to successfully mesh a complicated geometry for CHT in Star CCM+ for about 6 weeks with no success now. I cannot get a valid surface mesh to generate. I am always left with at minimum thousands of intersections in the surface mesh... the volume mesher cannot proceed as such. My CAD has no detectable errors in star ccm. I am using the 3D-CAD to perform my boolean subtractions / imprint for the parts. I have tried so many different options with meshing, tesselation, enhanced quality triangles, triangles, finer meshes, coarser meshes.... same issue every time -- tons of intersections left over, even with automatic surface repair. Surface wrapping is not an option because this will ruin the conformal interface I need for CHT. Can anyone offer some tips on how to get a valid surface mesh? I have reached out to Siemens, they are no help (our lab pays for premium support). I have access to the Ansys suite. Should I try meshing in Ansys then importing the mesh to Star CCM? I am nearly out of ideas. What's more: This is a single stage turbomachinery simulation. I can mesh the stator row independently with no problem. I can mesh the rotor row independently with no problem. When I do it all together, this is where it never works out. Add the repeating interface .... bad surface mesh. Don't even add the repeating interface before meshing, bad surface mesh. It doesn't make sense to me. Is it worth upgrading to the newest version of Star CCM+? We use 2021.3 because this is the newest version available on our HPC. I could upgrade, then export the mesh and import it back to the older version.

ashokac7 · June 17, 2022, 01:21

Yes. Surface repair for CHT can be harassing. I don't think getting new version will be much helpful. Sometimes it's better to try the file from scratch.

One thing you can try if you didn't already. Combine all the the parts into single part. In conventional parts node and not into 3D-CAD. Then imprint all the surfaces wherever needed. You can use single part imprint option. You will get blue edges (non-manifold) here which is perfectly fine. If surface imprinting is not working, delete 1 surface and pull edges from another to this one. It will again create blue edges. Finally we should only have blue edges in surface repair. All other repair parameters should be zero. Then perform split by topology by right clicking on part. This should give perfect geometry for CHT meshing will all the interfaces. You have to keep patience here. I have worked for 2-3 weeks on single geometry (containing 40-50 parts) in doing this.

Note- before combining make sure surface repair parameters are zero in each part separately. I hope this helps.

June 16, 2022, 16:08	Star CCM+ CHT surface mesh problems.. intersections wont go away.	#1
lelandt50 New Member Leland Join Date: Dec 2020 Posts: 6 Rep Power: 5	I've been trying to successfully mesh a complicated geometry for CHT in Star CCM+ for about 6 weeks with no success now. I cannot get a valid surface mesh to generate. I am always left with at minimum thousands of intersections in the surface mesh... the volume mesher cannot proceed as such. My CAD has no detectable errors in star ccm. I am using the 3D-CAD to perform my boolean subtractions / imprint for the parts. I have tried so many different options with meshing, tesselation, enhanced quality triangles, triangles, finer meshes, coarser meshes.... same issue every time -- tons of intersections left over, even with automatic surface repair. Surface wrapping is not an option because this will ruin the conformal interface I need for CHT. Can anyone offer some tips on how to get a valid surface mesh? I have reached out to Siemens, they are no help (our lab pays for premium support). I have access to the Ansys suite. Should I try meshing in Ansys then importing the mesh to Star CCM? I am nearly out of ideas. What's more: This is a single stage turbomachinery simulation. I can mesh the stator row independently with no problem. I can mesh the rotor row independently with no problem. When I do it all together, this is where it never works out. Add the repeating interface .... bad surface mesh. Don't even add the repeating interface before meshing, bad surface mesh. It doesn't make sense to me. Is it worth upgrading to the newest version of Star CCM+? We use 2021.3 because this is the newest version available on our HPC. I could upgrade, then export the mesh and import it back to the older version.

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June 17, 2022, 01:21		#2
ashokac7 Senior Member Ashok Chaudhari Join Date: Aug 2016 Location: Pune, India Posts: 260 Rep Power: 11	Yes. Surface repair for CHT can be harassing. I don't think getting new version will be much helpful. Sometimes it's better to try the file from scratch. One thing you can try if you didn't already. Combine all the the parts into single part. In conventional parts node and not into 3D-CAD. Then imprint all the surfaces wherever needed. You can use single part imprint option. You will get blue edges (non-manifold) here which is perfectly fine. If surface imprinting is not working, delete 1 surface and pull edges from another to this one. It will again create blue edges. Finally we should only have blue edges in surface repair. All other repair parameters should be zero. Then perform split by topology by right clicking on part. This should give perfect geometry for CHT meshing will all the interfaces. You have to keep patience here. I have worked for 2-3 weeks on single geometry (containing 40-50 parts) in doing this. Note- before combining make sure surface repair parameters are zero in each part separately. I hope this helps.