A simple UDF question
 

Hi Everyone,

I was reading one of Fluent's UDF examples in which the goal is to initialize the volume fraction of the secondary phase (UDF for initializing phase volume fraction). We all know that all the domains except the superdomain are not necessarily sequentially ordered; therefore, domain_id 3 does not necessarily mean the secondary phase. However, in this examples for finding the secondary phase the following is used

if (DOMAIN_ID(subdomain) == 3)

This does not make sense to me and I think the secondary phase should have been found with the aid of "phase_domain_index!"

Can somebody clarify the matter for me?

Cheers, Pirooz