append-mesh-data memory leak?
 

I've had this issue in Fluent v17 & v18. My guess is, it can happen in any version of Fluent. Does anyone know a workaround?

I'm running LES on a pipe flow and want to double the length of my pipe by appending the case-data.

/mesh/translate ## 0 0
/mesh/modify-zones/append-mesh-data " "

Then I start merging zones and surfaces etc. I can merge the cell zones no issue. But there is a huge memory leak when I try to fuse the overlapping boundaries and the interior zones.

/mesh/modify-zones/merge-ones fluid-1 fluid-1.1
this usually works okay. The next two always give me problems.
/mesh/modify-zones/fuse-face-zones wall-1 wall-1.1
/mesh/modify-zones/merge-zones interior interior.1

My mesh is currently only 7 million cells (x2=14 million). It shouldn't need more than 30 GB. However, when I run fuse-face-zones or try to do merge-zones on the interior I get a memory leak and the sim just asks for all the memory that is available >250GB RAM. Usually the fuse-face-zones will work (but uses ~210GB of RAM) and then the merge-zones interior will crash on a cortex error, probably because Fluent ran out of memory. In parallel goes just grabs all the RAM and crashes. In serial, it immediately throws a segmentation fault without hogging the memory.

I had ANSYS support look into the issue.

It seems using /mesh/modify-zones/merge-zones on interior zones is a known bug in Fluent and is not recommended. Merging interior zones is only needed for tidiness anyway so it's not a high priority. However, merging boundary zones i.e. /mesh/modify-zones/fuse-face-zones should work.

I erroneously reported that fuse-face-zones ran into a memory leak. It actually doesn't but it does need a lot of memory. Performing fuse-face-zones roughly doubles the memory needed for the mesh (temporarily). ANSYS ran my case on a bigger node than mine, with 300+ GB of RAM and it still ran out of memory. Even for small grids, ANSYS recommends to never merge interior zones because of this memory requirement.