Back flow in axial comperssor
 

DEAR SIRS
I NEED TO KNOW THE BEST BOUNDARY CONDITIONS USED IN MODELING OF AXIAL FLOW COMPRESSOR IN ANSYS CFX .
IF I USED INLET PRESSURE 1 Pa AND MASS FLOW RATE AT OUTLET =20KG/S
THE SOLUTION NOT CONVERGE ???I DO NOT KNOW WHY ??
THE PRESSURE RATIO =2.105

FAQ: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

And also read the best practises guide for turbomachinery in the CFX documentation.

i mean the best type of boundary condition (pressure inlet or mass flow rate inlet also pressure outlet or mass flow rate outlet)

Usually a mass flow inlet with a pressure outlet is best.

But this is all discussed in the documentation. You really should read it so you know the answers to these questions yourself.

Boundary conditions seems to be OK...
You can also give the following boundary conditions:
Inlet: massflowrate @ 20 kg/s
Outlet: Static Pressure

Try to put Y+ value correctly as found by the formula.

Apply SST turbulence model, if you are not having much experience in CFD.

I hope this will improve your convergence.