Doubt Regarding Boundary Conditions
 

I am trying to do truncated nozzle analysis with nozzle exit exposed to ambient pressure.

Following data are known to me
Chamber Pressure (Pc), Temperature (Tc) and gamma.
Ambient Pressure (Pa) and Temperature (Ta)

First I tried to do 2d planar, steady, implicit, inviscid analysis using ideal gas with following boundary conditions as shown in the images

Operating Pressure = 0 pa
With Nozzle Inlet as Pressure Inlet = P =Pc, T =Tc
With Nozzle Wall as Wall
Other Remaining Edges as Pressure Outlet = P =Pa, T = Ta

But it seems that my residuals are not converging but keeps on oscillating around 1.

I don't know the reason why this is happening, I have created structure mesh still it is oscillating.

Any help from your side would be appreciated.