Can I use thermophysicalProperties.water for "compressible" solver such as buoyantSim
 

Dear Foamers;

I want to simulate natural convection phenomena. And I do not want to use Boussinesq approximation. (In my problem, there is a large temperature difference)

When I tried with air properties, it seems to work well. (rho max/min : 1.2 1.0)
However, when I changed thermophysicalProperties for air to water..

the "rho max/ min" calculated over 2,000kg/m3.

What is the problem? :(

Hi Seokwon,

I have a similar problem, I think.

Firstly, have you adjusted rhoMin and rhoMax in fvSolution? (Silly question I know, but I forgot to do this)

Secondly, is your volume closed? If there is no inflow or outflow then you have the same fundamental problem that I do... See my post here:
http://www.cfd-online.com/Forums/ope...ed-volume.html

1. No, I did not adjust rhoMin/rhoMax...
2. Yes, volume closed problem.. :(

Ok, so the problem with closed volume and incompressible (to explain a bit more than my other post) is that at the start of your simulation, you do not know mow much mass there is in your system. For example, if you start off at 25C, and after 1 iteration the average temperature is 25.5C, the density will have changed, and if the volume is fixed, you cannot conserve mass (m=rho*V) properly.

One solution that I have seen implemented is to maintain a constant average temperature, therefore constant average density and constant mass. This will not, however, work for my case. I think you would have to do a lot of coding in the solver to implement this.

I would like to know if the idea of allowing a small inlet/outlet will still converge to a solution. This would only work for steady state. I am busy working on this at the moment. I will let you know if I find anything.

The other option is to allow the free surface to move/the volume to expand as required to maintain a constant mass. I have no idea how to start implementing this.

Thanks for your reply!
Actually, I did not think about mass conservation :(

How can I maintain a constant average temperature?
Do you have any experience to fix the code to solve this kind of problem?

+ my solver is compressible solver..

Which solver are you using? Are you solving for steady state or transient changes?

The only way I can think of maintaining a constant average temperature would require significant modification of the solver code. I recommend you start by spending a lot of time going through the solver code and understanding exactly what it is doing, and when. I am definitely not skilled enough to just tell you off the bat exactly what you need to do.