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Old   January 22, 2002, 10:00
Default USRSRC
  #1
Alex
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Hello,

I am simulating two phase (air and water) flow with homogeneous model. There are suspended solids in water . I want to impose the presence of solids in only one phase (water).

To this aim, I used USRSRC, with those values : Am=0 (for 6) SU=0 SP=1

But it doesn't work ?

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Old   January 27, 2002, 17:17
Default Re: USRSRC
  #2
Astrid
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use sp=-1
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Old   January 28, 2002, 04:41
Default What is USRSRC?
  #3
henry
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hi

What is USRSRC?

please brief be on this.

thanks

henry
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Old   January 28, 2002, 06:07
Default Re: USRSRC
  #4
Alex
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Astrid, Henry,

Thank you for your answer... I have tried both (sp=1, sp=-1) => Still does not work.

Prescribing a MASS FRACTION value works only when I use one phase approach (say for example water and sediments). I used a "user3D patch" on which I set : Su=0 and Sp~-1E10. I explain => The Matrix is writen (solver manual): ap*Mp = sum(nb){anb*Mnb}+Su with ap=sum(nb)-sp+sum(convectives flux)+time(term) {*}

If you want to prescibe Mp value (=V) : ap=1 su=V anb=0

But with USRSRC {for henry --> fortran routine wich allows "the skilled users" ;-) to add source and sink terms in equations} we can only change su, sp ,anb. But not ap. That is the reason why I have prescribe a big value for sp (~1e10) in order it prevails in ap calculation {*}.

For a two phase flow (air-water) + massfraction. It doesn't work. Why ? In CFX4.3 solver manual (pdf : page 3-746) it is said that the software is able to do that. I'am still "looking for details on how to do this"....

Alex,

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Old   January 28, 2002, 07:07
Default Re: USRSRC
  #5
Astrid
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'It doesn't work'. What do you mean by that? Do you get an overflow? Runtime error? Wrong position? No effect at all? Please be more specific.

Astrid
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Old   January 28, 2002, 11:05
Default Re: USRSRC
  #6
Alex
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I try two flow configurations.

1/ Dam break configuration (Ref29) ,in which I added 1 mass fraction equation. Initialy, the mass fraction field has a constant value.

For exemple : 2D case i=1..20 j=1..20 intial field for water => i=1..8 j=1..20 intial field for mass fraction => i=1..5 j=1..10 intial field for air=> i=9..20 j=1..20

After some time steps, the mass fraction field is diffuse in water and in air. massfraction goes accross the boundary between the two phases (air and water). while I am expecting no mass fraction in air. ----> It is why I say it doesn't work ...

2/ 2D Open chanel flow with massfraction transport equation. massfraction is injected at water inlet. I have still the same problem ...

Thank you for your Help

Alex

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Old   January 28, 2002, 11:17
Default Re: What is USRSRC?
  #7
Alex
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Hello

USRSRC --> fortran routine wich allows "the skilled users" ;-) to add source and sink terms in equations. You can find more at page 3-554 of solver manual.

If your source term is quite simple, you can use command language directly. I advise you begining with exemple reference 12, at first.

Alex

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Old   January 29, 2002, 17:13
Default Re: USRSRC
  #8
Astrid
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Up till now, I think you want to 'freeze' the flow (both liquid and gas) locally to simulate the presence of solids. Then you have to set am=0, Su=0 and Sp=-1 for u,v and w for the liquid and gas phase. This should work.

Why do you use a Mass fraction for the solids? Then, to keep the solids on their position, you have to define a density which is a function of the mass fraction. This will become tricky, especially as your mass fraction will diffuse through your domain, unless you take special care.

Does this help? (Sommige mensen........)

Astrid

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Old   January 30, 2002, 07:11
Default Re: USRSRC
  #9
Alex
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I think that I didn't clearly explain the case that I have to modelize.

The case deals with simualting an open chanel flow(exple: a river). I use the homogeneous model in order to calculate water depth variations. With this model I known where are located water and air fields.

Next I add sediments.

The river is loaded with solids that have settling velocity. This can be achieved using the Algebraic Slip Model with USRSLP when the problem is only : water and sediments (the interface between air and water, could be simulated as wall with "SLIP" bondary condition). But in my case, since the water depth variation is important, I have to know its location too. So I am forced to use the homogeneous model to track the water surface and a scalar transport equation (for sediments concentration field). The sediments are transported in water and not in the air. That is the reason why I want to use the USRSRC subroutine in order to avoid that sediments be present in air.

I hope that you have a better understanding on my problem. Perhaps if I have used the word 'sediment' instead 'solid' it would have been easier...

Know "it works"..You are right : am=0 Su=0 Sp=-1

I was mistaking while using IPALL... sorry...

Thank you for your help...

Alex

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