unbelievable problem in fluent
 

hi guys：
I am simulating a centrifugal compressor stage using ansys fluent which contains an impeller and a diffuser. the BCs： pressure inlet and mass flow outlet . in the simulation , the mass flow rate of the outlet is monitored. the plot showed that the mass flow rate of the outlet is oscillating , not equal with the prescibed value. another phenomena in the simulation is that the the console show the boundary mach numeber at the oultlet exceed the maximum limit .
how could it be ? can anyone have some method to sove this problem ?

thank !

I had mass imbalance problem for incompressible flow with similar bc's....i used mass inlet at inflow first and then switched to pressure inlet...it did fix my problem..i guess this way mass convergence is ensured and then the pressures are developed accurately after we switch bc...

thanks , i will try it .