Infinite Flow Volume

Project Support
1

I’m trying to create an internal flow volume of an HVAC duct system. All openings (inlets/outlets, highlighted in yellow) have been selected as a boundary face. However, SimScale still says the project still creates an infinite flow volume. Can anyone point out where it’s wrong? Thanks

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Project Link: SimScale Login

3

Hi @jbamaswag,

For an internal flow simulation, the flow region has to be fully enclosed by the surrounding geometry. In other words, the CAD model must form a watertight volume so that the solver can clearly identify which region is the internal fluid domain. If there are open surfaces, sheet bodies, small gaps, or non-manifold connections, the flow-volume extraction may fail because the software cannot distinguish the inside of the duct from the outside region.

In this project, the issue does not seem to be caused by the inlet or outlet selection. The main problem is that the geometry contains a sheet body, Surface 4. Since this surface is not a proper solid part of the duct assembly, the geometry is not fully closed. Because of this, the internal flow volume extraction leaks through the model, and SimScale detects the domain as an infinite region instead of a bounded internal flow volume.

This is also consistent with SimScale’s recommendation that sheet bodies should be solidified or removed before running the flow-volume extraction. These types of errors usually indicate that the enclosing geometry is not watertight.

I would suggest fixing the geometry first before continuing with the CHT setup:

  1. Remove or suppress Surface 4 if it is not needed.

  2. If Surface 4 is required, convert or thicken it into a proper solid body.

  3. Check the highlighted edges for small gaps, open connections, or non-manifold regions.

  4. Re-run the internal flow volume extraction once the duct assembly is fully closed.

  5. After the flow region is created correctly, continue assigning the CHT materials and boundary conditions.

Additionally, I would highly recommend you to take a look at this knowledge base article on creating a flow volume extraction.

Thanks!
Bryan