The following sections provide advice on applying boundary conditions:
To obtain the speed line performance of a turbomachine stage in steady-state analysis you can use one of the following approaches:
At the exit use a mass flow boundary from a stall point toward a near-choke point and pressure boundary from a near-choke point to a deep-choke point.
Use the exit corrected mass flow rate boundary condition, which enables you to traverse the speed line without changing the boundary condition type.
In a transient simulation it is recommended that you use a pressure boundary to traverse the speed line. This is particularly true when you are modeling a blade row flow problem on small sector of the wheel and using one of the pitch-change models.
It is very important to note that a mass flow boundary at the
exit should not be used with an incompressible flow setting. For a
more accurate representation of the pressure field at the outlet of
an axial machine, use a radially distributed pressure profile. If
you want to compare a transient solution obtained from reduced geometry
having pitch-change models (for example, Time Transformation or Fourier
Transformation) with a solution obtained from a full domain model,
then it is best to select a boundary condition setup that minimizes
the differences between the two simulations. Therefore, on the exit
boundary it is recommended that you use a pressure profile without
circumferential variation (thus, set Pressure Profile Blend
= 1). The pressure profile can vary radially.