Mesh interface generation
 

Hi,

I am simulating flow in a centrifugal compressor with the casing using MRF.
In doing so, I have two regions a casing fluid region and an impeller fluid region ( non conformal mesh ).

Now when i create an interface between them i notice that fluent creates extra interior and wall regions.

What are these extra wall and interior regions, should i be worried about them?
I am not being able to convert these extra walls into interiors ( the option doesnt exist, i can convert it into symmetry, velocity inlet,fan ,etc but not interior )

In the tutorials, it is mentioned that a shadow wall will be created in such a case, this does not happen in my case.

Thanks

The walls formed when part of the two interfaces are too far away from each other so that FLUENT can not figure out that they form a pair. The FLUENT will then isolate such regions and regard its type to be wall. You should check the area of the interfaces to make sure that they are approximately the same size as the physical geometry. Otherwise you might need to remesh your geometry.

Thanks for the reply!

However, i did make sure that the two parts were a perfect fit. I made both the regions in separate files in solidworks and made sure that the geometries were fitting together ... is there any way i can check which place in the geometry is the problem?

In most cases it is not a matter of geometry but rather mesh. For example when the mesh size differs significantly across a cylindrical face then there is a great chance that additional walls will form. It is normal for the appearance of these walls. But you should make sure that the area of the interfaces in the mesh-interface pairs are approximately the same as the original geometry surface.

I have attached a picture of my current mesh.

To get a conformal mesh at the interface i grouped the two parts together (form new part) and then meshed the geometry. However after doing this i can only name one of the two interfaces ( either the casing interface or the impeller interface). Once i do that, that one named selection appears as an interface in fluent, i changed that to wall. upon doing this i get the wall and shadow wall which i convert to interior ( like in the tutorial ).

Is my previous approach ok ( the attached image ) or should i covert the non conformal mesh at the interface to a conformal mesh?

I have attached a picture of my current mesh.

To get a conformal mesh at the interface i grouped the two parts together (form new part) and then meshed the geometry. However after doing this i can only name one of the two interfaces ( either the casing interface or the impeller interface). Once i do that, that one named selection appears as an interface in fluent, i changed that to wall. upon doing this i get the wall and shadow wall which i convert to interior ( like in the tutorial ).

Is my previous approach ok ( the attached image ) or should i covert the non conformal mesh at the interface to a conformal mesh?

You do not have to do any change yet. It is normal to have auto-generated walls if you use mesh interface in a non-plain geometry. Issue the TUI command
to check whether the interfaces cover most of the area.

Hi,

Thanks for the reply, I checked and all the walls seem to have e-6 areas where as the interfaces have e-2 areas, also the interface-interior zone has e-2 areas. So i guess i can move forward with this method right ( the non conformal mesh ) ?

This was the output
List of Mesh Interfaces


Interface Name: int5
Interface Options: none


Description Name ID Area
----------------------------- ----------------------- ----------- -------------------
Interface-Zone-1 interface5 15 0.038263798
Interface-Zone-2 interface5.5 20 0.038264133
Interface-Interior-Zone interior-32 32 0.038244449


Interface Name: int4
Interface Options: none


Description Name ID Area
----------------------------- ----------------------- ----------- -------------------
Interface-Zone-1 interface4 14 0.095427677
Interface-Zone-2 interface4.4 19 0.095432743
Boundary-Zone-1 wall-30 30 3.6739158e-07
Boundary-Zone-2 wall-31 31 3.7120976e-06
Interface-Interior-Zone interior-29 29 0.095370732


Interface Name: int3
Interface Options: none


Description Name ID Area
----------------------------- ----------------------- ----------- -------------------
Interface-Zone-1 interface3 13 0.059391819
Interface-Zone-2 interface3.3 18 0.059389576
Boundary-Zone-1 wall-27 27 1.935465e-06
Boundary-Zone-2 wall-28 28 2.0191237e-08
Interface-Interior-Zone interior-26 26 0.059356477


Interface Name: int2
Interface Options: none


Description Name ID Area
----------------------------- ----------------------- ----------- -------------------
Interface-Zone-1 interface2 12 0.095428362
Interface-Zone-2 interface2.2 17 0.095432967
Boundary-Zone-1 wall-24 24 4.7417069e-07
Boundary-Zone-2 wall-25 25 3.4288305e-06
Interface-Interior-Zone interior-23 23 0.095373005


Interface Name: int1
Interface Options: none


Description Name ID Area
----------------------------- ----------------------- ----------- -------------------
Interface-Zone-1 interface1 11 0.038263865
Interface-Zone-2 interface1.1 16 0.03826417
Interface-Interior-Zone interior-8 8 0.038245097

Yes, I think you can move on.

Thanks for the answers!

This is a very interesting conversation. So much so that I tried something myself.

I created two cylinders from same circle and created simple mesh with ansys meshing. I used patch-controlling method to ensure that the faces have same meshes. Despite utmost care when I import the mesh to fluent I still see the additional walls in the boundary list. Although I can not edit the properties of these walls.

I also checked the interface area with 'define/mesh-interfaces/list' command and the areas of all three: source-wall, target-wall and the interior match perfectly.

Although everything seems to be alright but I have two question that either of you can answer. 1. The additional walls are created even if the area and mesh of the faces sharing the interface are matching perfectly. Is this correct?? 2. If these additional walls are redundant i.e. I can not edit their properties, is it ok to delete them? (Not that they are bothering me or something) 3. What % error is acceptable?

Hello
I face the same problem then I extruded one face with solid extrusion in design modeller and check by Boolean operation if its uniting perfectly then walls are not created in between the interface,
Please check the mesh sizing it should be almost same at the both the interfaces