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surface tension equation as source term

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Old   April 12, 2020, 01:25
Default surface tension equation as source term
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Ghazi
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Hi everyone,

I want to write a UDF for the surface tension equation(source term in the momentum equation of the VOF model ) as the attached file.
Can anyone help me with that?
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File Type: docx Surface tension.docx (36.5 KB, 31 views)
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Old   April 13, 2020, 04:27
Default Surface Tension
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What is the objective behind writing this UDF? Both, CSF and CSS, models for surface tension force modeling are available as inbuilt models in Fluent.
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Old   April 13, 2020, 04:53
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Quote:
Originally Posted by vinerm View Post
What is the objective behind writing this UDF? Both, CSF and CSS, models for surface tension force modeling are available as inbuilt models in Fluent.
Dear Sir,

I tried to simulate steam condensation phenomena inside a tube, I came to know from different literature that existing modules of ANSYS FLUENT are not well versed to model two-phase flow simulation i.e. specifically when it comes to steam [properties & state both varies with process parameters], therefore, I activated the source terms in mass and energy equation, and I want to activate the surface tension force in the momentum equation to the VOF modeling to straightforward my work.

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Old   April 13, 2020, 06:11
Default Udf
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Surface tensions models are meant for only multiphase flows; single phase does not have a surface, consequently no surface tension or its requirement for modeling

Anyway, if you want to include source term, then you need to use DEFINE_SOURCE macro. Look at the following for the examples

https://www.afs.enea.it/project/nept...udf/node49.htm

Since the source needs to be applied only at the free surface, you need to check for the cells containing free surface, i.e., cells with C_VOF for any of the phases between some acceptable values, say, between 0.3 and 0.7. A more sophisticated approach is to check for its gradient to identify the cells containing the free surface but checking the value of C_VOF also works good. And then, just apply the source term in the cells matching the criterion.
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Old   March 23, 2021, 21:00
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Quote:
Originally Posted by MohammedGhazi View Post
Dear Sir,

I tried to simulate steam condensation phenomena inside a tube, I came to know from different literature that existing modules of ANSYS FLUENT are not well versed to model two-phase flow simulation i.e. specifically when it comes to steam [properties & state both varies with process parameters], therefore, I activated the source terms in mass and energy equation, and I want to activate the surface tension force in the momentum equation to the VOF modeling to straightforward my work.

Greetings
MohammedGhazi
Hey where you able to successfully write a UDF for the source term? I'm stuck with the source term udf as I'm facing issues with handling the vector and scalars involved.
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