Empty Surfaces_help
 

Hello CFD enthusiasts.

For my Honours thesis this year I am conducting CFD simulations using ANSYS Fluent in Workbench. Currently I have encountered some difficulties with empty surfaces and zones being created when my meshed model is imported into Fluent from Meshing, as seen in Zonesurface.PNG.
Referring to Console.PNG, the last three zones were note created by me and appear when the model is first opened in Fluent.
Attached is a capture of the meshed model in Fluent for reference if needed. I will also note this is my first post on CFD-Online.

It would really be appreciated if someone could help me mitigate this problem. I am aware I can delete the Surfaces in Fluent through the Zone surface management.

Please let me know if you can help.

Thanks in advance
Thomas Kinney

Those empty walls come from your interface.

You have an interface (or 'contact' in workbench-terms) between "fluidinterface" and "airinterface".
In general, when you make an interface between to surfaces, some cells might match and some cells might not match.

Suppose for simplicity that your two surfaces are like this:
Then there are four kinds of cells:
A: cells on the side of 'airinterface' that match cells from 'fluidinterface'.
B: cells on the side of 'airinterface' that don't match cells from 'fluidinterface'.
C: cells on the side of 'fluidinterface' that match cells from 'airinterface'.
D: cells on the side of 'fluidinterface' that don't match cells from 'airinterface'.

Types A and C are obviously the good ones. They are named airinterface-contact_region_src and fluidinterface-contact_region_trg in your case.

Types B and D are the bad ones. In your case, Fluent puts them in the zones "wall-18" and "wall-19". It looks like that as of Fluent 17, the names of these zones are more descriptive of what they are, they would have been something like "airinterface-contact_region_wall_src" or so.

Fluent is a bit annoying with these zones ("wall-18"):

• They can not be removed.
• They are always reported as having area 0, even if they don't.
• They can not be plotted.
• Even if your interfaces match perfectly so these zones should really be empty, they still show up.

My way to deal with them: if you know your interfaces are good so these zones should be small or empty, ignore them.
Only exception: if you are doing particle simulations, and these 'empty walls' are set to trap particles, and particles are reported as being 'trapped' on these empty walls, you need to know which interface they are associated with if you want to know how to do statistics with these particles.