Incompressible ideal gas

Nadaaaa22 · September 6, 2019, 12:07

I would like to ask why in the ideal gas natural convection flow the governing equations should be coupled but in case we choose the incompressible ideal gas the governing equations (mass,momentum and energy) can be decoupled?. Can someone please explain this to me i’m lost?.

Nadaaaa22 · September 7, 2019, 15:12

There is no answer?!.

fluid23 · September 12, 2019, 15:52

Generally speaking, a segregated (or as you put it, decoupled) solver is not good at handing anything beyond a mildly compressible flow. For incompressible flow, a segregated solver will get you an answer faster than a coupled solver. However, a compressible flow with appreciable compressibility is likely to be unstable if run with a segregated solver. Since natural convection is driven by boyancy which is a product of density, you could run into issues with a segregated approach.

Did something prevent you from setting up a segregated compressible ideal gas flow? Just curious what precipitated this question.

September 6, 2019, 12:07	Incompressible ideal gas	#1
Nadaaaa22 Member Join Date: Nov 2018 Posts: 41 Rep Power: 7	I would like to ask why in the ideal gas natural convection flow the governing equations should be coupled but in case we choose the incompressible ideal gas the governing equations (mass,momentum and energy) can be decoupled?. Can someone please explain this to me i’m lost?.

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September 7, 2019, 15:12		#2
Nadaaaa22 Member Join Date: Nov 2018 Posts: 41 Rep Power: 7	There is no answer?!.

September 12, 2019, 15:52		#3
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Generally speaking, a segregated (or as you put it, decoupled) solver is not good at handing anything beyond a mildly compressible flow. For incompressible flow, a segregated solver will get you an answer faster than a coupled solver. However, a compressible flow with appreciable compressibility is likely to be unstable if run with a segregated solver. Since natural convection is driven by boyancy which is a product of density, you could run into issues with a segregated approach. Did something prevent you from setting up a segregated compressible ideal gas flow? Just curious what precipitated this question.