[UsamaQ]

Hello.

I am trying to run steady state simulation of compressor in CFX. I have created an initial mesh which results in convergence.

However, If I try to generate inflation layer on blades surfaces with appropriate inital layer thickness, I get very very large aspect ratio and expansion ratios and simulation diverges in CFX. The inflation layer looks fine but why aspect ratios are that high? How can I reduce this? Is it due to large element size?

I have attached the quality check report from ICEM.

[Gert-Jan]

Difficult to say. We need geometry and mesh.
Looking at the numbers it are the 2454 elements with very sharp angles (<6°).

If you click on the bar of this group in the histogram using your Right mouse button, you can create a subset. Then in the tree on the left hand side in the mesh menu, you can make these visible and it will show you where the problem is.

[UsamaQ]

I have attached the geometry and mesh images. You can see inflation layer on the surface of blades with zoom in in 3rd picture.

[Gert-Jan]

Well, what do you think yourself?
Think about the volume ratio between the last inflation layer and the first tetrahedral element. This should be closer to 1. You need to increase the number of layers, increase the growth ratio, decrease the tet size.
There are so many options. Try out a few to see what it brings.

[hitzhwan]

Originally Posted by Gert-Jan

Difficult to say. We need geometry and mesh.
Looking at the numbers it are the 2454 elements with very sharp angles (<6°).

If you click on the bar of this group in the histogram using your Right mouse button, you can create a subset. Then in the tree on the left hand side in the mesh menu, you can make these visible and it will show you where the problem is.

I can not find the option, could you send me an image?

[Gert-Jan]

This only works in ICEM to which UsamaQ refers. Do you use that?

[hitzhwan]

Originally Posted by Gert-Jan

This only works in ICEM to which UsamaQ refers. Do you use that?

Yes, I use that

[Gert-Jan]

You cannot grab this in a picture. It is a procedure which requires a animation. Too much work for this free helpdesk.
So, again, if you plot the quality (edit mesh -> Quality), you get a histogram on the right hand side. If you click on one of the bars of the histogram with your right mouse button, you get the option to create a subset. Do this.
Then, in the tree on the left hand side, open the mesh tree, go to subsets, and tick the just created subset to visualise the elements in the subset.

[UsamaQ]

Hello Gert-Jan.

As mentioned above, to reduce the aspect ratios, I increased number of layers, growth ratio and reduced the tetra size (number of elements increased from 2M to 46M) but still aspect ratio is of the order e8. I don't understand why it is happening.

Also, I checked Y plus in post for non inflation case and it is quite high and is in e3 to e4 range. What can I do now? How to improve the mesh further. I am using patch conforming tetra mesh and already sitting at 2M elements.
Thank you

[Gert-Jan]

In Icem you can locate the nasty elements. Also in Post you can ask for mesh statistics, create variables to plot volume ratios etc.
Based on that you need to refine the mesh locally. And as long as you aren't specific, I can only direct you to general options. E.g., in ICEM you can create a volume density to define local refinement. It is also possible to refine along a curve. Alternatively, split surfaces and add a refinement on the smaller nasty surfaces.

[UsamaQ]

Thanks for the information. Can I do local refinement by creating a volume density in workbench meshing? Because I only used ICEM for mesh quality report.

[hitzhwan]

Originally Posted by Gert-Jan

You cannot grab this in a picture. It is a procedure which requires a animation. Too much work for this free helpdesk.
So, again, if you plot the quality (edit mesh -> Quality), you get a histogram on the right hand side. If you click on one of the bars of the histogram with your right mouse button, you get the option to create a subset. Do this.
Then, in the tree on the left hand side, open the mesh tree, go to subsets, and tick the just created subset to visualise the elements in the subset.

Thank you, got it. Do you know how to use Mesh software?

[Gert-Jan]

Yes. I know how to use Mesh software.

[Gert-Jan]

Originally Posted by UsamaQ

Thanks for the information. Can I do local refinement by creating a volume density in workbench meshing? Because I only used ICEM for mesh quality report.

Not that I know. You can create a refinement (Insert Sizing in Mesh tree) on a surface or edge and then add a region with constant size (radius of influence, or similar).

[hitzhwan]

Originally Posted by Gert-Jan

Not that I know. You can create a refinement (Insert Sizing in Mesh tree) on a surface or edge and then add a region with constant size (radius of influence, or similar).

I do this， but I find there is a discontinuous for the inflation and the face mesh connected to it， how to decide the curvature normal angle in the mesh size?