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-   -   help!porous! (http://www.cfd-online.com/Forums/phoenics/63390-help-porous.html)

9527 April 7, 2009 05:02

help!porous!
 
dear all:
i have some questions to ask:
1.is "porosity" only used in type "plate"?But vpor and epor etc can be used anywhere by patching?
2 how "vpor" influence the flow ,is there a pressure drop when use the "vpor".
3.i want to simulate the resistance in the porous for fluid,but which model should i choose between the DARCY law and Ergun Equation.who can tell me their difference.
4.i want to simulate the fluid flow thru the 3D porous .the property of porous can affect the flow ,how can i edit the the property of porous .

Stel April 22, 2009 08:51

porous in phoenics
 
Hi,

the porosity feature is not restricted to the plate object. You can apply a porosity factor to any control volume of the domain, by means of a PATCH (WHERE you want to apply the porosity) and an INIVAL (which specifies the value of the porosity)
Below, I put an example of a porosity algorithm I made using InForm. The objective is to multiply the east and north areas and the volume of cartesian-grid control volumes in order to transform them numerically in cylindrical-coordinate volumes. What I did was to find a relation, for a given y-mesh configuration, between a cartesian volume and a cylindrical volume. You may notice that the values of the INIVAL fields are functions of the position YG, but you're able to apply any numerical factor you wish.
Hope this helps you.

inform11begin

PATCH (POE1,INIVAL,1,nx,1,1,1,nz,1,1)
(INIT of EPOR at POE1 is (yg[&1&]) with fixval)

PATCH (POEY,INIVAL,1,nx,2,ny,1,nz,1,1)
(INIT of EPOR at POEY is ((yg[&&]+dyv[&&]/2)+(yg[&-1&]+dyv[&-1&]/2))/2 with fixval)

PATCH (POV1,INIVAL,1,nx,1,1,1,nz,1,1)
(INIT of VPOR at POV1 is (yg[&1&]) with fixval)

PATCH (POVY,INIVAL,1,nx,2,ny,1,nz,1,1)
(INIT of VPOR at POVY is ((yg[&&]+dyv[&&]/2)+(yg[&-1&]+dyv[&-1&]/2))/2 with fixval)

PATCH (PONY,INIVAL,1,nx,1,ny,1,nz,1,1)
(INIT of NPOR at PONY is (yg[&&]+0.5*dyv[&&]) with fixval)

inform11end

Stel April 22, 2009 08:57

Porosities
 
Important: do not forget to write on the Group 7 of the q1 file that the porosities you want (EPOR, NPOR, HPOR, VPOR) must be stored...
in my case above, this would be:
STORE(EPOR,NPOR,VPOR)
Good luck!

Koolifant April 23, 2009 03:19

Dear Stel,
Why do you do a transformation to polar coords. I don't get the point i guess.

Stel April 23, 2009 07:25

Dear Koolifant,

at the time I made this transformation I was wishing to use periodic boundary conditions for circular corrugated ducts. Since in PHOENICS there's no "z-cycle" boundary option, I needed to adopt a cartesian coordinate system with the axial direction of the pipe disposed in the x-direction so I was able to apply the "x-cycle". So, I assumed the corrugated pipe wall as a corrugated plate and applied porosity to numerically transform the squared faces in polar faces. Now I manually apply the "z-cycle" option in polar coordinates using In-Form, PATCHES and SOURCES, but the transformation feature was the only way I found until I didn't now how to self introduce the periodic condition in polar coordinates. Actually I wrote that as an example on how can this guy apply a porosity factor to any face or volume, but if someone would be interested in the transformation option I could post something for it; it works pretty well!

Stel April 23, 2009 07:36

Important again Mr. 9527:

The porosity factors just multiply areas and volumes. At the time of the integrations, the real areas will be multiplied by numerical factors that are going to NUMERICALLY reduce their values. Being said that, I think that there's no influence on the flow other than restrict the flow rate (as a porosity field should be). If you prescribe a pressure gradient through sources, don't forget to multiply them by VPOR, ok?

Hope this helps you! Good luck!

9527 April 27, 2009 03:34

THANK YOU Stel very much!!!

Stel April 27, 2009 07:30

You're welcome, any questions post here and maybe together we find a solution! Good luck!

9527 April 27, 2009 22:52

Hi Stel
when i want to simulate the resistance producted by the porosity.which model should i choose between the DARCY law and the Ergun Equation.As far as i know,the DARCY law is used for the gas flowing in the porous ,and the Ergun Equation is used for the liquid ,am i correct?

Stel April 29, 2009 17:44

Hi Mr. 9527

unfortunately, I can't give you assistance about resistance in porous media because I never studied about it. Sorry, hope someone else helps you on it. But if you find problems on implementing the porosity fields on phoenics, maybe I can give you helpful advices. GL!


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