CFD-ACE compressible flow convergence problem

DelphineL · October 12, 2009, 10:48

Hello everybody!

I would like to simulate a reservoir of water & air, heated from outside and observe the natural convection due to density change with temperature.

I use for that CFD-ACE

But I have convergence problem:

If I set the air & water density as constant, it converges, but I will never see natural convection
If I set the air compressible (ideal gas law) & the water constant, it converges. But the water is just a first step before a simulation with propane, so I would like to make it compressible
If I set the air with constant density & the water with piecewire linear with T, it does not converge.
==> all the other parameters are kept similar...

So the problem is obviously coming from the compressibility of the water...

Did anyone already try to simulate natural convection with 1 liquid and 1 gas on top of each other?

Thanks a lot in advance!

DelphineL · October 21, 2009, 05:50

Hello!

I know that nobody repplied, but, just in case someone could be interested by this question:
the problem is that CFD-ACE does not support a solution with 2 phases with changing density, especially because of a parameter called "reference density".
Therefore, the best is to set the reference density to the one of the liquid, and for the gas, add a flow source as a subroutine, that is linked to convection: like g*(rho - rho_ref)*V

I still need to implement this subroutine because I never did it, so if one of you already implemented a USOURCE, please let me know!

October 12, 2009, 10:48	CFD-ACE compressible flow convergence problem	#1
DelphineL New Member Delphine Laboureur Join Date: Oct 2009 Location: Brussels Posts: 3 Rep Power: 16	Hello everybody! I would like to simulate a reservoir of water & air, heated from outside and observe the natural convection due to density change with temperature. I use for that CFD-ACE But I have convergence problem: If I set the air & water density as constant, it converges, but I will never see natural convection If I set the air compressible (ideal gas law) & the water constant, it converges. But the water is just a first step before a simulation with propane, so I would like to make it compressible If I set the air with constant density & the water with piecewire linear with T, it does not converge. ==> all the other parameters are kept similar... So the problem is obviously coming from the compressibility of the water... Did anyone already try to simulate natural convection with 1 liquid and 1 gas on top of each other? Thanks a lot in advance!

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October 21, 2009, 05:50		#2
DelphineL New Member Delphine Laboureur Join Date: Oct 2009 Location: Brussels Posts: 3 Rep Power: 16	Hello! I know that nobody repplied, but, just in case someone could be interested by this question: the problem is that CFD-ACE does not support a solution with 2 phases with changing density, especially because of a parameter called "reference density". Therefore, the best is to set the reference density to the one of the liquid, and for the gas, add a flow source as a subroutine, that is linked to convection: like g(rho - rho_ref)V I still need to implement this subroutine because I never did it, so if one of you already implemented a USOURCE, please let me know!