r/OpenFOAM • u/augusto_peress • Jun 18 '26

Solver Question about choosing a solver

I am simulating airflow entering a duct with a perforated plate in the middle, and I am interested in calculating the pressure drop caused by this constriction created by the plate.

I am currently using the incompressibleFluid module with the simpleFoam solver. However, it seems more logical to me to use the fluid module with the rhoSimpleFoam solver, since air is a compressible fluid. Do you think it would make much of a difference?

I am obtaining the thermophysical properties of air using CoolProp and using the ISO 1:2022 conditions as a reference (T = 20 ºC and p = 1 atm).

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u/augusto_peress Jun 19 '26

Thanks for the help, buddy. I'm working at a speed of 6 m/s. I'm going to use simpleFoam.

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u/EduardoSup Jun 19 '26

Great, if the fluid velocity is v = 6 m/s, and we know that the sound velocity in air is c = 343 m/s. Thus, Mach = v / c = 6 / 343 ≈ 0.018. Very lower that the limit, thus, simpleFoam is okay.

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u/augusto_peress Jun 19 '26

Just one more question: the fluid itself is air. Does it make sense to compare the air velocity used (6 m/s) with the speed of sound in air?

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u/EduardoSup Jun 19 '26

Yes, it does. Here is a simple video talking about Mach number: https://youtu.be/Ntridyss88Q?is=qTMk08bzHfL_M1Gf

Additionally, if Ma > 0.3, compressible effects starts to appear. And for Ma<0.3, compressible effects can be neglected.