Steady versus Unsteady models!?
 

When precisely should I be using a steady model versus an unsteady model?

I get appropriate drag co-efficient's for a cylinder at Re~1E+4 using a steady approach, but values that don't match the experimentally accepted values when using time-averaged URANS.

Should I be using unsteady for all applications, or only when there is likely to be turbulence within the boundary layer and not the free stream / wake.

I want to go on to model aerofoils.

Any help is appreciated.

Cheers,

~Asa