Unable to create boundary layers for vehicle aerodynamics CFD wrapped surface

Subodh Gokhale_20466

Hello

I have generated wrapped surface of a vehicle, surface meshed it and made sure that there are no intersections, non-manifold and free edges. The domain basically consists of wrapped vehicle surface and a box which encloses the vehicle. I want to volume mesh the air domain around vehicle. I am able to generate tet volume mesh.

However, i am unable to generate CFD mesh and boundary layers. I tried boundary layer mesh control but still not able to generate boundary layers. To start with, i am trying to generate just a single layer of 0.5mm thickness. I have attached the snapshot of the mesh settings.

I get following error when i try to do CFD volume mesh: Error:: Box1 Mesh failed.

This is not sufficient information and i can not figure our what is wrong and pin point the cause. 

Regards,

Subodh

AlessioLibrandi

Hi, not easy to understand the settings, but I would try to suggest you some typical steps.

I would select the internal faces (i.e., the wrap faces) and select REVERSE NORMAL on right-click.

Then, I would use the option MERGE to put both bodies (box and wrap) into a single one (right click MERGE after selecting bodies).

So you should have one single body to mesh, with an external and an internal surface. This could make it work.

Subodh Gokhale_20466

Hello Alessio

Thanks for the response and suggestions.

I will try above settings and let you know.

I did merge all bodies into a single body(box+wrapped surface) and then tried volume mesh but it did not work. The wrapped surface is generated from sheet bodies which have thickness. Therefore wrapped surface is a closed surface overall, however it also has closed loops(the thickness of parts/bodies would be hollow). I did think of reversing the normal but i was specifying the node point in the volume of interest so thought it would not be needed. However i will check reversing normal and let you know.

How to visually check surface normal in Simlab?(HyperworkCFD has an option by which surface normal is represented by a color)

I also thought that there could be really narrow regions where boundary layer generation is not feasible. I did try to check surface element angle(say greater than 140) in quality check but there were many such elements and i am not sure if there is any way to auto-fix them. I tried mesh quality control to limit this angle when doing surface mesh but i still end up getting such elements.

I have tried playing with other advance options in an attempt to stop boundary layer before reaching narrow regions but so far i have failed.

Regards,

Subodh

AlessioLibrandi

Subodh Gokhale_20466 said:

Hello Alessio

Thanks for the response and suggestions.

I will try above settings and let you know.

I did merge all bodies into a single body(box+wrapped surface) and then tried volume mesh but it did not work. The wrapped surface is generated from sheet bodies which have thickness. Therefore wrapped surface is a closed surface overall, however it also has closed loops(the thickness of parts/bodies would be hollow). I did think of reversing the normal but i was specifying the node point in the volume of interest so thought it would not be needed. However i will check reversing normal and let you know.

How to visually check surface normal in Simlab?(HyperworkCFD has an option by which surface normal is represented by a color)

I also thought that there could be really narrow regions where boundary layer generation is not feasible. I did try to check surface element angle(say greater than 140) in quality check but there were many such elements and i am not sure if there is any way to auto-fix them. I tried mesh quality control to limit this angle when doing surface mesh but i still end up getting such elements.

I have tried playing with other advance options in an attempt to stop boundary layer before reaching narrow regions but so far i have failed.

Regards,

Subodh

 

To visualize normal:

ydigit

If the issue is still unresolved, I would suggest either uploading the SLB file here or asking for a meeting with Altair Support. 

Subodh Gokhale_20466

Hello all

We have managed to generate first 1 boundary layer using the "boundary layer" option available in "3D mesh".  The interior generated surface mesh of the boundary layer had intersections and we had to manually remove them. Then we generated tet mesh of this interior surface without boundary layer. Finally, we merged core mesh with the boundary layer mesh.

However, we are not able to generate multiple boundary layers so far with this technique.

We are still failing to generate CFD mesh(with and without BL) using "Mesh-->CFD mesh" option.

We are trying to use coarse mesh and see if we are able to generate boundary layers.

We have also contacted altair support for further help.

We have however managed to generate 5 boundary layer CFD mesh in hypermesh!!

Regards,

Subodh

ydigit

Please try with the "CFD" icon and BL mesh using this method. 

I am unsure what happens in case of Boundary Layer only. The "CFD" icon based method should be the one used by defaul for CFD. If it does not work, please create a ticket and ask for a support meeting. 

 

Sagaya Prasanna Kumar Savarimuthu

Hello Subodh Gokhale,

This is Prasanna, CFD Analyst at SimLab. Thanks for reaching out through Altair Community.

Could you be able to join a call to discuss the issue you are facing with CFD meshing? If yes, please drop a mail to sagayas@altair.com.

By the way, the 3D mesh > Boundary layer is not the apt tool for CFD meshing. I recommend CFD mesh tool for all meshing purposes for CFD problems.

Regards,

=Prasanna.

Subodh Gokhale_20466

Sagaya Prasanna Kumar Savarimuthu said:

Hello Subodh Gokhale,

This is Prasanna, CFD Analyst at SimLab. Thanks for reaching out through Altair Community.

Could you be able to join a call to discuss the issue you are facing with CFD meshing? If yes, please drop a mail to sagayas@altair.com.

By the way, the 3D mesh > Boundary layer is not the apt tool for CFD meshing. I recommend CFD mesh tool for all meshing purposes for CFD problems.

Regards,

=Prasanna.

Hello Prasanna

I was finally able to generate boundary layers+core mesh using CFD mesh. I used the "Fraction of surface mesh size" option for First layer thickness definition and am able to generate complete mesh. Thank you very much for this solution!!

I do have a question. I am able to successfully generate volume mesh when surface mesh count was around 5 million(3mm mesh size) and then the final element count is around 80 million(50mm mesh size). However, when the surface mesh count was around 15 million(2mm mesh size), i noticed from the temp files that the core volume count was 120 million and the process was still in progress even after leaving it overnight. I had to finally kill the process. My system RAM is 32 GB and I would like to know if the issue is due to insufficient memory.

Regards,

Subodh

acupro

Subodh Gokhale_20466 said:

Hello Prasanna

I was finally able to generate boundary layers+core mesh using CFD mesh. I used the "Fraction of surface mesh size" option for First layer thickness definition and am able to generate complete mesh. Thank you very much for this solution!!

I do have a question. I am able to successfully generate volume mesh when surface mesh count was around 5 million(3mm mesh size) and then the final element count is around 80 million(50mm mesh size). However, when the surface mesh count was around 15 million(2mm mesh size), i noticed from the temp files that the core volume count was 120 million and the process was still in progress even after leaving it overnight. I had to finally kill the process. My system RAM is 32 GB and I would like to know if the issue is due to insufficient memory.

Regards,

Subodh

Most likely due to lack of memory/RAM - as 20 Million elements is getting quite large.  Did you check the memory usage prior to killing the process?