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-   -   CavitatingFoam psil psiv (http://www.cfd-online.com/Forums/openfoam-solving/59045-cavitatingfoam-psil-psiv.html)

kyubi March 10, 2008 06:22

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

Thank you!

schmidt_d March 10, 2008 12:09

Marco, As in most OpenFOAM ap
 
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 March 10, 2008 13:30

Thank you for your quickly rep
 
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 March 12, 2008 11:13

Marco, The equations for ma
 
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 July 31, 2009 09:07

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 October 7, 2009 05:10

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. żDo you know what's the difference between rholSat, rhovSat and rhoMin?

Thanks

srakshit December 9, 2009 14:39

Quote:

Originally Posted by jml (Post 231724)
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. żDo 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 June 3, 2014 07:06

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.

Quote:

Originally Posted by vw.cfd (Post 224859)
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.


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