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Old   April 4, 2008, 05:36
Default DEFINE_PROPERTY(diameter,c,t)
  #1
bohis
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Hello, If I use this macro to define diameter of secondary phase in Euler-Euler model, cell thread is thread of secondary phase. Am I right?

thanks in advance!!
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Old   April 7, 2008, 07:21
Default Re: DEFINE_PROPERTY(diameter,c,t)
  #2
Aris
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No, t is the thread of secondary phase. c is a pointer to the current cell. Fluent loops over all cells of your domain.

Be carefull with changing the diameter. I believe that fluent increases/ decreases volume fraction when you do such a thing in order to conservate the mass
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Old   April 7, 2008, 08:07
Default Re: DEFINE_PROPERTY(diameter,c,t)
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bohis
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waw, thanks a lot, why does Fluent change the volume fraction? I just wanna change diameter depending on coordinates. Do you know how Fluent handles between diameter and vof?

uff, thank you very much
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Old   April 7, 2008, 09:41
Default Re: DEFINE_PROPERTY(diameter,c,t)
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Aris
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I'm not sure. Just check it out! If you see the equations there shouldn't be any problem. But if you for example reduce the diameter from 300μm to 200μm isn't there a mass loss? I had some problems in the past with this. Just check it out.
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Old   April 7, 2008, 10:16
Default Re: DEFINE_PROPERTY(diameter,c,t)
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bohis
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you are right! I have also loss of mass! strange, I will check it out and let you know. Anyway, my routine is wrong, so I must firstly repair then, maybe, problem will disappear.

thank you!
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Old   April 8, 2008, 04:10
Default Re: DEFINE_PROPERTY(diameter,c,t)
  #6
Aris Nikolopoulos
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I'm very interested in this. If you find something please let me know
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Old   April 10, 2008, 09:58
Default Re: DEFINE_PROPERTY(diameter,c,t)
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bohis
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ehmm, now it is really clear, that there is mass and momentuum loss in domain, if I adjust the diameter every timestep. Unfortunately, I do not know why. I would expect Fluent to retain the volume fraction. It doesn´t! It means that I need other UDFs for defininig sources. Doesn´t it?

any suggestions?
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Old   April 10, 2008, 10:21
Default Re: DEFINE_PROPERTY(diameter,c,t)
  #8
Aris Nikolopoulos
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No, the problem isn't with the UDF. I believe you should find the mass loss in the secondary phase and you should adjust it to the correct value in a UDF.
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Old   April 10, 2008, 11:23
Default Re: DEFINE_PROPERTY(diameter,c,t)
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bohis
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This could be expression for source for continuity equation:

source = (vof*density/d^3)*(d^3-D^3)*velocity

vof = volume fraction of water before diameter adjustment d = diameter before breakup D = after breakup

ehm, since it is euler euler model there should be then also mass loss of primary phase. That means, if I have energy equation off, there will be 4 sources. mass and momentum for each phase. Am I right? friend, check me please.

have a nice day
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Old   April 11, 2008, 07:09
Default Re: DEFINE_PROPERTY(diameter,c,t)
  #10
Aris Nikolopoulos
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About Source terms. In your case i believe that the best way is a "patch". For example when you enter your UDF before any change of your diameter find the mass of water. Then change your diameter and afterwards rechange your mass in the cell (not with source term!).

Nevertheless as now i see what you want to do i believe the best way to model breakup is population balance model. Check it out! Do you have the kernel for the breakup? A little complicated model (pbm)but very good. In 6.4 fluent there is a very good upgrade for population balance model.

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Old   April 11, 2008, 07:57
Default Re: DEFINE_PROPERTY(diameter,c,t)
  #11
bohis
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Hi and thanks for the reply!

Regarding PBM, I do not have a license for that anyway. How would you change the mass? C_VOF(c,t) ? which macro would you use for hooking new vof?

thank you again!
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Old   April 14, 2008, 06:41
Default Re: DEFINE_PROPERTY(diameter,c,t)
  #12
HP
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C_VOF(c,t)=0.1; For example will cet volume fraction in that cell 0.1
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