Stream Function physical significance?

ram

What is the physical significance of stream function? What does it give us physically? If it does not give any info physically, why is it introduced? Already Fluid flow is complex!!! (I am looking for the physical significance as we have for vorticity).

Are momentum equations and energy equations coupled for forced convective flow? Or can they be solved independently.

As far as my knowledge goes, only in free convection, the momentum equations and energy equations are coupled.

How does one take flow induced temperature variations into account for solving for velocity field and temperature field? Whenever we perform analysis for temperature field and velocity field, the boundary conditions are externally imposed, not internally imposed/generated.

With Best Regards

Ram Prakash