I have to carry out a steady simulation with CFX.

I defined a outlet boundary condition at the outlet. The flow is assumed to be subersonic there.

But during the calculation I found out that the flow at the outlet is in some steps supersonic and in other steps subersonic.

I want to konw whether I should swith the boundary condition from the current subersonic outlet boundary condition to the supersonic outlet boundary condition or not.

How are I deal with this problem properly?

Thanks.

Hi nina

What are you modelling. What is your mach number? If your mach number is in the range of supersonic flow, only then you should switch your outlet BC to supersonic.

Regards

i requested that please send the definition of outlet boundary and zero normal gradient condition.