[kyubi]

Hi!
Can anyone explain me the meaning of "psiv" and "psil" in cavitatingFoam/nozzle2D/constant/thermodynamicProperties/?

Thank you!

[schmidt_d]

Marco,
As in most OpenFOAM applications, psi in cavitatingFoam is the derivative of density with respect to pressure. Here, the v and l appended to psi refer to the vapor and liquid, respectively.
-DPS

[kyubi]

Thank you for your quickly reply David!

I'm also trying to figure out which are the governing equations used in cavitatingFoam, but I'm not able to understand it only from the source code...
Can you help me again?

Marco

[schmidt_d]

Marco,

The equations for mass & momentum are the standard single phase, variable density versions, since cavitatingFoam is using a pseudo-fluid approach. The user can choose various compressibility models (see the compressibilityModels sub-directory in the source). I am most familiar with Wallis' model. The derivation is given in his text book, which is now out of print. The compressibility model sets the value of psi as a function of mixture fraction, which feeds into the pressure solution. Unfortunately, I find that you can run into serious stability problems when the density ratio between liquid and vapor is extreme.

I once tried an approach where you analytically integrate Walllis' relationship. It worked well for very high speed flow and small length scales, but required specialized non-reflecting BC's.

@Article{Schmidt1999b,
author = {D.P. Schmidt and C.J. Rutland and M.L. Corradini},
title = "{A Fully Compressible Model of Cavitating Flow}",
journal = {Atomization and Sprays},
year = {1999},
volume = {9},
}

The openFOAM implementation is more general and can run at low Mach #.

-David

[vw.cfd]

hi,

I was wondering how to calculate 'psil' and 'psiv'?
does anyone know the value of psiv for a vapour like air?

pls help!

[jml]

Hello Schmidt, I have seen that you talk about the Wallis model. I'm setting the thermodynamicproperties file, but I have three parameters of density. ¿Do you know what's the difference between rholSat, rhovSat and rhoMin?

Thanks

[srakshit]

Originally Posted by jml

Hello Schmidt, I have seen that you talk about the Wallis model. I'm setting the thermodynamicproperties file, but I have three parameters of density. ¿Do you know what's the difference between rholSat, rhovSat and rhoMin?

Thanks

rholSat --> Liquid Density at Saturation Point (i.e. at equillibrium)

rhovSat --> Vapour Density at Saturation Point (i.e. at equillibrium)

rhoMin --> very low value of density used to keep the density positive (value of 0.1 is fine)

[A_Pete]

I know it's an old thread, but since I was looking for this myself I felt like I should at least answer to this post, after having found the answer.

Originally Posted by vw.cfd

hi,

I was wondering how to calculate 'psil' and 'psiv'?
does anyone know the value of psiv for a vapour like air?

pls help!

'psil' can be calculated as psil = 1/a_l^2 , where a_l is the sonic speed of the liquid phase. Same goes for 'psiv' and the appropriate sonic speed of the vapour phase.

[mm66]

Originally Posted by A_Pete

I know it's an old thread, but since I was looking for this myself I felt like I should at least answer to this post, after having found the answer.




'psil' can be calculated as psil = 1/a_l^2 , where a_l is the sonic speed of the liquid phase. Same goes for 'psiv' and the appropriate sonic speed of the vapour phase.

Hi Foamers,

I was going through the tutorial for cavitatingFoam. It mentions [0 -2 2 0 0] as the unit for both psiL and psiV. So it is:

rho * isentropic compressibility (Bs)

where Bs*rho is the inverse of (speed of sound)^2:

Bs*rho = 1/c^2

If isothermal compressibility (Bt) is instead available, then Bs can be calculated using:

Cp/Cv = Bt/Bs

I appreciate if you please correct me if I am wrong here.

Regards,
MJ