Problem about species source terms
 

Hi, i defined three species and i know only two species equation will be solved in FLUENT. Right now, i defined species mass source term for the two species. My question is whether i need to define the exactly same magnitude source term in continutity equation ("mass source" in boundary condition) in order to satisfy the mass conservation. If not, why is it not necessary?

Re: Problem about species source terms
 

Hi! You do not need to introduc the third mass source, because Fluent calculates that auotomatically.

Davide.

It will calculate 3d mass fraction, as 1 - 1st - 2nd, at least that is more or less written in users guide, or at least I understood it that way.
There are udf examples in which is explicitly written that all species sources should be also defined under mass sources.

This is ANSYS FLUENT support answer:
#785
Why is no mass imbalance observed after applying source term for species?

Answer:

Species sources are not accounted for in mass imbalance in the solver as it should have been taken care of automatically within the solver. If it was not, users must explicitly define a mass source term equal to the species source term.

It is not completely clear to me...