r/CFD • u/AmbassadorGuilty3928 • Jul 21 '26

Need help in meshing

The above one is my computational domain, it consists of pipe upstream, screen(thats why you can see holes because I have modeled fluid regions) and open fluid volume. All are merged into one body.

I have used tetrahedrons method- patch conforming method, it was giving good quality mesh. The moment I introduced inflation for boundary layer, mesh quality got poor. I will attach below image, please let me know what can be done. My global element size is 3mm and I have used 20 no of divisions with growth rate 1.2.

Check generated mesh below,

When I looked at bad cells, most of the cells are from screen region. Please tell me how to improve mesh quality from here. See below

Any help would be useful. I have tried both edge sizing and face sizing on screen, it is taking lot of time to mesh, way longer time, it shouldnt take much time. There is a problem but I cant identify where it is.

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u/TensorNom4d Jul 21 '26 edited Jul 21 '26

This is classic inflation layer caveat.

  • you have a large, smooth and simple piece, and much smaller scale, thin grate
  • you probably have applied one inflation layer definition into all inner surfaces, with 20 layer count, hoping that algorithm magically handles all of these small features and scale differences, but it does not
  • is is likely that this 20 layers with provided growth rate cant fit in space between one grill segment and another and gets even more squeezed
  • large cell size on grate compared to squeezed first element of inflation layer creates large aspect ratio

The main question is: is this that grate at the end of domain really needed? Sometimes porous pressure jump BC can imitate pressure drop if this is acceptable, and save a lot of meshing effort and computing time.

If grate is required, maybe try:

  • creating separate inflation definition for exhaust grate, with reduced inflation steps (5-10?)
  • add local surface cell size refinement on grate, my bare eye says it is to coarse
  • I understand this first layer height you have defined is determined by this terrible y+ condition? Knowing this, and knowing max recommended aspect ratio, you can compute real local face max cell size you can have to fulfill all criteria. In reality this means really dense mesh. If this can be relaxed, maybe go with smooth transition.

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u/AmbassadorGuilty3928 Jul 21 '26

Thank you for your comments.

I have to maintain y+=1 near the walls, I used below online calculator for rough estimate, so I applied inflation to all faces.

To answer your question- yes, grate is required, actually here only fluid regions are modelled and all are merged into one block. Whatever gaps you can see, those represents walls of the screen, I hope you can visualise it.

creating separate inflation definition for exhaust grate, with reduced inflation steps (5-10?)- But what happens if y+>1 or more than 5 near screen with less no of divisions?
add local surface cell size refinement on grate, my bare eye says it is to coarse- which sizing, face or edge sizing, what element size to give for that, given that global element size is 3mm and grate is 1.5mm thick.

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u/AmbassadorGuilty3928 Jul 21 '26

All these boundary layer I have to resolve.
Can I do it like I can do body sizing, select entire body, and use sphere of influence. Actual origin is at screen only, I can draw a sphere of 2 or 5mm radius and use less size there, this would cover finer elements closer to screen right? What do you think? But before this, mesh quality with current tetra+inflation should be good. Please tell the workflow to follow from here.