[stark_zh]

Hi everyone,
i have been simulating my engine model with AMR in converge. I wanna set a Temperature trigger in AMR but i dont know how should i set up the sub-grid criterion. I've tried many times and the sub-grid velocity trigger worked like i expected but in the output amr.out the subgrid_scale temperature in combustion chamber is always the 2.5 which i defined in the sub-grid criterion. I dont really understand that. Dose it mean the amr for Temp-Criterion was all time triggered ? And should i try with higher sub-grid temp criterion?

By the way, dose anybody have experience how we could do a mesh study like convergence analysis or just a study which discuss the relationship of cell count and the accuracy of the results in converge?

I hope someone understand my question and would help me. Thx in advance.

[MFGT]

Hi,

regarding the subgrid_scale in amr.out
I think its always set to the value you defined, except if your cell count is limited by amr_max_cells of amr.in. Then the subgrid scale is increased so you maintain the limit but still create cells where most needed. If you make the subgrid scale smaller, more cells are created.

Regarding a mesh study. You could simply set up a standard case with 4mm base mesh (and fixed embeddings, AMR etc.) and the do multiple copies with base mesh 3, 5, 6, 7, 8 mm and so on... of course you can also chose non integer values like 4.5mm

Then comparing results, you should see some values converge at higher grid sizes (e.g. Tumble), but some need lower ones (e.g. TKE)

[stark_zh]

Thank u very much Tobias,
so i could consider the Sub-grid criterion just as a tolerance for the amr? The smaller i have defined the tolerance(sub-grid criterion) the more cells are needed for a more detailed value (But the Max is what i defined the Max. embedding level)? Is that right?

For the Mesh study. Is it possible to vary with AMR or Fixed Embeding and i just leave the base grid untouched? Will that be meaningful with amr. I am not sure cuz AMR is adaptiv. When it works, question is that, which value should i vary in AMR settings? The Max. embedding level or the Subgrid criterion?

Thank u!

[Yaju]

Hi,


Subgrid scale value decides where (spatially) the refinement is going to happen. Lower the value more locations will get refined.



The embed_scale decides how fine the refinement can be.


I would suggest you to run your cases with an embed_scale of 3 for both velocity and temperature. And then reduce your base grid size for your grid refinement study.