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-   -   transportProperties for compressibleInterFoam (http://www.cfd-online.com/Forums/openfoam/68727-transportproperties-compressibleinterfoam.html)

 romant September 30, 2009 06:36

transportProperties for compressibleInterFoam

Hej,

I have a question about the variable "psi" in the transport properties dictionary for compressibleInterFoam. I assume that it is the compressibility. The problem is, that compressibility has a different unit from the one given [0 -2 2 0 0], from the depthCharge2D case. For some reason psi is only given there with 5 instead of the 7 dimensional parts.

How do I have to understand psi?

thnx,

~roman

 haghajani October 27, 2009 10:27

psi and density

Hi Romant,

Have you find out what is the reason of introducing unit of "psi" by five element instead of seven?

Do you know why the compressiblity is 1e-5 for both Air and Water? And the reason, this technique has been used to deal with density? I mean definig rho[phase] = rho[0] + psi[phase] * p

Thank you in deep,

Hamed

 romant October 27, 2009 10:50

I at found out that the definition of the last 0 seems to be not important for the solution. I tried the same run with a proper 7 dimension definition and it did not change anything.

The reason why psi is the same for both water and air is because then the difference is not as big and the system converges faster, giving shorter computation time. in the end this is just a tutorial.

the method of defining rho the way it was defined is a simplifaction and does not take into account that there a temperature change due to the compression of the fluid.

also, I only set rho[0] for my incompressible fluids and let the pressure and the psi decide for compressible fluids what the density should be. (incompressible fluids get rho[0]=0).

from this calculation one can easily determine what psi should be for the gas. for water it is around 10^-10

 piprus November 6, 2009 09:06

Could you tell me, how should I understand rho and rho0? What are the meanings of them.

Can I say that rho0 is the initial density and rho is a final or calculated density? Or maybe I should treat rho0 as a reference density? I'm a bit confused now.

 romant December 2, 2009 17:25

rho is the calculated density. and rho0 is a fixed initial density. for example for water there is not way one will compress that with normal conditions. so when the pressure changes, one does not want to have the density of water changing.

psi and p then calculate the increase in density. but since the compressibility for water is in the range of 10^-10 this will not change anything.

rho0 is not set for compressible phases

 reza_65 June 14, 2011 04:21

compressibleInterFoam tutorial

hi everybody
i don't know anything about the tutorial of compressibleInterFoam of OpenFoam 1.7.1
how could i know what 's it?what 's the simulation for, and what are the Fluids, usage...
thank you