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Diffrent permeability in deffrent drections

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Old   April 14, 2005, 00:27
Default Diffrent permeability in deffrent drections
  #1
billow
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Hi everyone

i have two questions in my work with phoenics 1)how can i do when the permeability in x-y(horizontal)drection is different from z(horizontal) drection. 2)when the air generates from a hull space, how to set the source term?

thanks for your help
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Old   April 14, 2005, 22:02
Default Re: Diffrent permeability in deffrent drections
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mick
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Hope I'm not misunderstanding.

If you mean permeability as in resistance to the flow, then you can administer sinks of momentum to the flow equations.

I believe that these are of the form Force=K.rho.U*U/2

where K is called the resistance coefficient.

This can be included within PHOENICS by patch/coval statements.

as K.(T).rho.U/2(0-U) , so Coeff=K.rho.U and Val=0.0

and the patch should be of appropriate geometric type (T) to make the source in correct units Newtons. The T comes in from the patch Type. (VOL/CELL/EAST etc)

I believe there are various engineering formulas for K based on the application. If you google for "resistive coefficients" you should find plenty of ideas.

Anistropic resistance will be set by applying different forces to the different flow directions.

2) Not sure what you mean? But if you want to generate a source of momentum form a space, then you do it directly through patch/coval and co=fixflu Val="the source", see POLIS.

But this type of thing can be done indirectly through the menu, creating objects such as FANS to say fix a velocity or create a user_defined object and attach a source to it.

If the air is a fresh supply rather then a stimulation of existing air, then you should set a mass source and and appropriate momentum source. i.e. an INLET This is all directly done through the Patch/Coval, but can be done easily and indirectly through the menu system

The PATCH/COVAL for mass (P!) should have a coeff=fixflu and a val = kg/s and an area type multiplier. An appropriate momentum source will need to be set, which gives a velocity generating the above mass inflow.

This will apply over the same patch as for mass and have a coeff=onlyms and a VAL=m/s.

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Old   April 18, 2005, 11:32
Default Re: Diffrent permeability in deffrent drections
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billow
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thank you,your answer helped me alot sorry for my poor english
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Old   June 6, 2005, 21:56
Default Re: Diffrent permeability in deffrent drections
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billow
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Sorry,recently I still in trouble about the source seting What I want is let the porous media in Packed Vessel generate gas continuously and no other inlets. the unit is such as m3/m3*S.

Wish mick help me again. Others'advice are also welcome.
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Old   August 9, 2005, 11:00
Default Re: Diffrent permeability in deffrent drections
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Andrea
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