How to model an airflow over a water?

Luk

Hi all, I want to model very simple situation. The hot air blows over an cold very dense and viscous other liquid flow and heat them. The problem is that I dont want to model momentum transfer between air and the other fluid (just to avoid convergence problems since I know that the influence of air on the second dense fluid can be neglected). Because of that I dont want to model it in single domain like in "Flow over a bump tutorial". Time ago Glen from this forum suggested to build a model with two separated domains (one for air and second for this other fluid) and make interface. However my problem is that it is impossible to include one fluid for first of domains and another for second one. If I set 2 fluid in one domain automatically these fluid occures for second one and it starts all the problems with momentum transfer etc. Convergence is very slow. Can anyone explain how to set different fluid for different domains as there will be only one fluid in each of domains?

I would be very grateful, Luk