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-   -   [ICEM] Getting the right mesh for simulation (http://www.cfd-online.com/Forums/ansys-meshing/111279-getting-right-mesh-simulation.html)

dcggames January 2, 2013 09:58

Getting the right mesh for simulation (Combustor, volume mesh)
 
Hi all,

I'm relatively new to meshing, and having some issues meshing a geometry for a current project.

I need to simulate the combustion/flow within a jet-engine combustor.
The combustor geometry has been created in Inventor 2013.

I need to be able to mark the inlets/outlets, which are holes/openings in the geometry. I figured I needed to create a volume mesh in order for that to be possible.

I imported the geometry as a STEP file in ICEM CFD 14.0 and went to the Global Mesh Setup menu. I choose the following settings:
Volume mesh.
Mesh Type: Tetra/Mixed.
Mesh Method: Robust(Octree)
Edge criterion at 0.2
Smooth mesh is checked.
Iterations at 5.
Min quality at 1.
Fix non-manifold checked.

At the Compute Mesh menu I choose the following additional settings:
Create Hexa-Core is checked.
Select geometry is all.

With these settings I get a, atleast, complete mesh. But it needs more refinement/quality to be accurate to the geometry.

Even more important, after importing the mesh in CFX, I noticed that I cannot select the holes/openings.

Clearly I'm doing something wrong. Whats the correct way to do it?

Regards!

dcggames January 4, 2013 20:20

Trying very hard not to be too unpatient...:p

But an idea anyone? I'm kinda stuck :(

diamondx January 6, 2013 18:13

post some screenshot... you want refinement, give small size for you elements...

CFD_SIM January 7, 2013 02:41

Like dimondx said some pictures would be nice!

I import my geometry also from Inventor, but I was not satisfied with importing it as a step-file. Sometimes there were just missing some cuts or holes. So now I am importing the geometry as a parasolid binary file. Maybe this will help you with that problem.

Another thing is that you sometimes get your geometry as one whole part, so you might wanna look into that and just create new parts and connect your splines and surfaces to the right part.

If you are a new in meshing i can recommend you documentation for ICEM (if you don't have it in your ANSYS file you can download it from the costumerportal on the ANSYS Homepage). There you will find a lot of informations regarding the improvement of a mesh, especially how to use the prism layers right.

Hang in there, at the beginning it's always really frustrating! But it will get better...

dcggames January 7, 2013 13:17

Quote:

Originally Posted by CFD_SIM (Post 400424)
Like dimondx said some pictures would be nice!

I import my geometry also from Inventor, but I was not satisfied with importing it as a step-file. Sometimes there were just missing some cuts or holes. So now I am importing the geometry as a parasolid binary file. Maybe this will help you with that problem.

Another thing is that you sometimes get your geometry as one whole part, so you might wanna look into that and just create new parts and connect your splines and surfaces to the right part.

If you are a new in meshing i can recommend you documentation for ICEM (if you don't have it in your ANSYS file you can download it from the costumerportal on the ANSYS Homepage). There you will find a lot of informations regarding the improvement of a mesh, especially how to use the prism layers right.

Hang in there, at the beginning it's always really frustrating! But it will get better...

Thanks for the kind words, that helps my motivation!

This is the geometry, it consists of 3 parts. Green is the liner, blue is the fuel nozzle and red the swirl vanes.

http://img43.imageshack.us/img43/1331/ss1tli.png

I tried to get some more info out the documentation and played around with the settings.

Scale factor 1, Global Element Seed Size 2048.
Tetra/Mixed, Robust (Octree), Edge criterion 0.2, Iterations 5, Min quality 1, Fix-non manifold.

Selected prism layer for the liner only, with 0 height.

I also created a density. With size 32, entity bounds, and selected all entities.

I selected "Create Prism Layer" and deselected "Create Hexa-Core".

With this as a result:

Without volumes:
http://img541.imageshack.us/img541/7087/ss2wv.png

And with volumes:
http://img43.imageshack.us/img43/1228/ss3zcb.png

Any good or??? :confused::D

Still need some extra refinement to get the swirl vanes shaped OK, and I need to change the max element size?

diamondx January 7, 2013 13:34

your mesh doesn't look smoothed to me, this happens if icem finds a hole in the geometry. did you get any notice for that ???

dcggames January 7, 2013 18:45

Quote:

Originally Posted by diamondx (Post 400553)
your mesh doesn't look smoothed to me, this happens if icem finds a hole in the geometry. did you get any notice for that ???

Hi Ali,

Of course also thanks for your help. Much appriciated!!

I did get prompted to fix a hole in the geometry. I clicked "No".

If I click yes it wants me to select edges. I'm not sure what the correct approach would be for that..

Just FYI, if I imported the mesh like it is on the above screenshots, I am stil not able to select any openings as inlets/outlets in CFX.

CFD_SIM January 8, 2013 02:58

Did you try to save the Inventor file as a parasolid? This normally helped me, but maybe you have to make some adjustments in Inventor, too. Regarding the inlet and outlet stuff.

Can you choose the Inlets and Outlets as parts? The whole wall looks like one part so if that is the case it's clear that you can't select the Inlets/Outlets in that area.

In my last project I just used the default settings for the mesh. (No max element size, just Zero) The only thing that I had to change was in the part mesh setup the max size (always depends on your geometry which value you choose).
And for a small gap I set a mesh density with entities (choosed some surfaces around that area). That normally is enough, but you can also play a bit with the scale factor and the edge critieria.

Could you share your geometry, so that we could have a look or is it classified?

dcggames January 8, 2013 06:29

Quote:

Originally Posted by CFD_SIM (Post 400659)
Did you try to save the Inventor file as a parasolid? This normally helped me, but maybe you have to make some adjustments in Inventor, too. Regarding the inlet and outlet stuff.

Can you choose the Inlets and Outlets as parts? The whole wall looks like one part so if that is the case it's clear that you can't select the Inlets/Outlets in that area.

In my last project I just used the default settings for the mesh. (No max element size, just Zero) The only thing that I had to change was in the part mesh setup the max size (always depends on your geometry which value you choose).
And for a small gap I set a mesh density with entities (choosed some surfaces around that area). That normally is enough, but you can also play a bit with the scale factor and the edge critieria.

Could you share your geometry, so that we could have a look or is it classified?

No in this case its not. Although I would like to avoid unnescessary spreading. I will send you and Ali a PM.

I used a Parasolid file, as you suggested. With this as a result:
http://img254.imageshack.us/img254/1088/ss4x.png

Still not 100%, as you can see.

I also tried meshing using DesignModeler.. The quality of the output mesh was fine, but because I was told that if I want to simulate the flow through the combustor I needed to create a volume mesh in ICEM which should cover all the openings as surfaces so they will be selectable.

So thats why.

Of course I can create a 'plate' at both the air inlet and the outlet in Inventor, but for the fuel inlet and the side air inlets that will be difficult. I tried filling the openings with DesignModeler, which works, but in CFX I get troubles with isolated interfaces on the, lets say 'walls' of the holes. So no luck either..

diamondx January 8, 2013 09:51

you have holes, holes, holes and hundreds of holes .... :D this just can't be meshed like that. you need to close all the holes, ALL OF THEM. create a body inside, and then mesh you geometry. Try closing the holes, get back to us when you will have problem again. we troubleshooted the problem, it's just a matter of time now until you get a good mesh... no need to worry anymore ;)


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