Problem with multi stage compressor simulation.
 

Hello everybody,
I am now try to do steady state CFD simulation for 4 stages axial compressor, I setup my study in CFX software using Total pressure boundary condition at Inlet and Static pressure at outlet, Mixing plane interface between Rotor and Stator, I try both the K- epsilon and SST for turbulence model, the calculation convergence good but when I change the Outlet static pressure to build the compressor map, the pressure ratio of first stage nearly fixed, and the result is the mass flow rate also fixed when overall pressure ratio varied, near chocking condition, fourth stage has negative efficiency, the pressure ratio smaller than 1(result attached). I think there are some problem with my setup or we need some special setup for multistage compressor simulation?
I already find some document related to this problem and they said that we need setup a 1D mapping static pressure after each component to initiate the calculation, I try it but don't know exactly how it work. I for multi stage compressor simulation, I don't know how the solver calculate, it calculate first stage, then the second, third, and four or it calculate all stage same time?
So anyone who knows about this domain, please help me to answer my problem, what should i do?

Thank you so much for kindly help and comment?

Overall performance
Pt inlet (atm) Ps outlet (atm) Massflow (kg/s) Pressure ratio Efficiency (%) Fourth stage efficiency
1 1 8.787 2.7263 62.1965 -42.9465
1 2 8.787 2.7768 62.6145 -36.5791
1 3 8.787 3.5142 75.6912 57.4889
1 4 8.787 4.4064 81.7028 84.8327
1 4.3 8.7867 4.6866 82.6718 85.8868
1 4.4 8.7864 4.7809 82.7443 85.3851
1 4.45 8.786 4.8285 82.552 84.345
1 4.48 8.7857 4.857 82.5053 83.9966
1 4.49 8.7867 4.8658 82.4494 84.6137