Nozzle analysis
 

Sir,
i want to do transient analysis of convergent nozzle.

For boundary conditions:

Fluid : ideal air.
Inlet: subsonic and supersonic conditions, i know pressure at inlet,velocity also. for steady state analysis i want to vary pressure.
outlet: pressure ( I WANT TO SPECIFY- how to specify). relative pressure i take 0 bar

wall condition: no slip
turbulent model :K-Epsilon

for transient condition:

refering to Fluent tutorial:
Pexit(t)=0.12sin(wt)+Pexit

how to specify time step

how do i proceed?

I tried with steady state specifying mass flowrate at inlet and pressure at exit but i is not converging.i think by boundary conditions are wrong...
please suggest me