Source term in volume fraction equation

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gunjanauti posted this 19 April 2019

I am trying to solve a multi-phase model with evaporation happening. I have already developed a theoretical model for the evaporation (different from Lee's Evaporation-Condensation model). How to hook the volume fraction equation source term in fluent? 

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Kremella posted this 19 April 2019


The VoF equation is a continuity equation for volume fraction and contains mass transfer terms in the RHS. The source term you are developing through a UDF has to be a mass source term. To include the effect of these terms, you have to hook the term to the Phase Interaction dialog box. 

Please have a look at the following sections in the Fluent Theory Guide (FTG) and Fluent User's Guide (FUG).

  • Section 26.2.10 - Including Mass Transfer Effects (FUG).
  • Section 18.3.4 Volume Fraction Equation (FTG).
  • Section 18.7 Modeling Mass Transfer in Multiphase Flows (FTG).

I hope this answers your question.




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gunjanauti posted this 20 April 2019

Thanks for the help though I used a different approach while solving the problem. I used a source terms for both my phases in cell zone conditions. It is working but is that the correct approach?

And one more thing I wanted to ask was that, I want to initialize a flow as an inverted annular film flow, while doing that I am able to initialize the volume fraction correctly but wasn't able to link the temperature and velocity profile. Even though I have used a DEFINE_INIT function, the GUI for the initialization shows the default values. So which values is the solution using? 

kkanade posted this 5 weeks ago

please check function hook. here you may need to hook your udf for initialization. 

gunjanauti posted this 4 weeks ago

I have hooked the function already and yet it initializes the flow with different values than the given function in UDF. Is there something to do with patching?



abenhadj posted this 4 weeks ago

Define Init overrides any field initialization. If temperature is defined in an Init UDF than it would take precedence.

Best regards,


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