Concentration dependent surface tension

ling

Hello,

I am using a VOF model, with a free surface of water and air. A chemical species is floating on top of the water and is changing the surface tension of it at the interface.

I would like therefore, to write a UDF of surface tension cofficient that is dependent on the chemical species concentration, under the multiphase, "interaction" option.

I am also using the DEFINE_PROPERTY udf. But the problem is ... what should I put for the thread in the C_YI(c,?,species_index) ? it is at the interface, so, which is it ? the air, the water or the mixture ?

I tried several sub or super thread options but none worked.

Any advices ? Thanks in advance !!