[Ulbas]

Hi everyone,

I’m working on an indoor airflow simulation in STAR-CCM+, and I’m looking for best-practice advice on meshing strategy and inlet modeling for a ventilation system with many nozzles.

Case description:
– Large swimming hall with a high ceiling (9 meters at the highest point)
– Supply air via textile ducts mounted under the ceiling
– The ducts have multiple small nozzles, oriented downward
– Expected air jet throw is approx. 8-9 m from the nozzles down into the occupied zone
– Exhausts are placed two seperated places close to the floor in the first floor

Current meshing approach:
– One large Air region with a relatively coarse base mesh for most of the hall volume
– A local volumetric mesh control below the textile ducts, extending approx. 8-9 m downward to resolve the supply jets
– The refinement volume is currently ~3 m wide × 8 m high, with finer cells to capture jet development
– The goal is to keep the total cell count manageable while still resolving jet behavior and room air distribution

Main questions:

For this type of ventilation system, is it considered better practice to:
– Model each nozzle explicitly as a separate velocity inlet, or
– Replace the nozzles with a single equivalent inlet surface / slot representing the total momentum and mass flow?

If using an equivalent inlet approach, what is the recommended way to:
– Preserve jet throw and momentum
– Define inlet velocity vs mass flow
– Choose inlet area and direction

Regarding meshing:
– Is a local volumetric refinement region following the jet path the correct strategy?
– How wide would you typically make such a refinement region for an ~8 m jet (to account for spreading and possible angled discharge)?
– Would you recommend multiple refinement levels (inner jet core + outer entrainment zone)?

Are there any common pitfalls when meshing downward ventilation jets in large indoor volumes (e.g. excessive cell counts, convergence issues, over-refinement near the nozzle)?

The simulation focus is overall airflow patterns, jet penetration into the occupied zone, and air mixing — not detailed nozzle-internal flow.

Any guidance, rules of thumb, or references would be greatly appreciated.

Thanks in advance!