how to chose the flow model in immiscible multi-phase tube flow simulation?
 

I wnna simulate a case with two different types of fluids via FLUENT and the fluids are im-miscible. the Renold number is low(500-7000). How should I chose the flow model? laminar or turbulent model? And how to decide to chose the model,just via Renold number or there are other standards to chose the flow model?