### 11.6.5. Boundary Conditions in Blade Row Simulation

The following sections provide advice on applying boundary conditions:

- Steady-state Analysis
- Transient Analysis

#### 11.6.5.1. Steady-state Analysis

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.

#### 11.6.5.2. Transient Analysis

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.

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