[Raja23]

Hello everyone,

I am new to UDF and I am working on adding a source term to a VOF model. I am trying to understand the "real dS[]" term. On going through the Fluent UDF manual, I understood that this is a derivate term of the dependent variable in the transport equation. But I am not clear about the two options that Fluent provides,
ds[equ] = ds/d(phi) (for implicit)
ds[equ] = 0.0 (for explicit).
Can someone explain, when should i choose the derivate term to be the real derivate and when should i just enter 0.0 as the derivative value? Thanks.