Initial Condition and State

The Initial Condition and State are volume conditions in the Flow module pertaining to selected Volumes. Specify Initial Condition and State in the Flow module as follows:

Geometric Entities Panel > Volumes > [Desired Volume]
Properties Panel > Model Tab > Flow > (Initial Condition or State)

Initial Condition

This refers to the values of the independent variables used to start a simulation when Start from Initial Values is selected in the Simulation Panel. For the Flow module, the initial velocity and pressure fields can be specified for each volume (Figure 5.106).

The Initial Condition can be specified either for a rotating volume (Rotating System) or non-rotating volume (Specified Values). Global expressions can be used to set the initial specified values for both pressure and velocity.

For a Steady-state solution, the Initial Condition serves as an initial guess and should have no effect on the final solution. However, for the sake of convergence, Initial Conditions should be as close to the final answer as possible.
For a Transient solution, the Initial Condition represents the flow and pressure fields at time equals zero. Once a transient solution achieves steady or periodic conditions, Initial Conditions have no effect on the solution. However, prior to achieving steady or periodic conditions, they have an effect on the solution. Initial Condition should represent physical values at time equal to zero or be as close to the final answer as possible.

Specified Values

This allows to specify the initial Velocity and Pressure field for a selected non-rotating volume.

Rotating System

This allows to specify the initial velocity and pressure field for a selected rotating volume using the following options: Pressure, Rotational Direction, Rotational Speed, Rotational Center, Rotational Axis Vector and Axial Velocity Component.

The default value of the Axial Velocity Component is 0.1 (m/s).
For a Steady-state solution, the initial Axial Velocity Componentserves as an initial guess and should have no effect on the final solution.
For a Transient solution, the initial Axial Velocity Component represents the axial velocity at time equal to zero. Once the solution achieves steady or periodic conditions, the Initial Conditions have no effect on the solution. However, prior to achieving steady or periodic conditions, the Initial Conditions do have an effect on the solution and should represent physical values at time equal to zero or be as close to the final answer as possible.
If the State of the Volume is set to Blanked, the valve of the axial velocity in the volume will be frozen to the initial Axial Velocity Component. This can be incorrect if the value does not correspond to what would be physically realistic, e.g. if the default of 0.1 m/s axial velocity was displayed in a solid.

State

The State of a Volume determines whether velocity and pressure are solved (Active) or not solved (Blanked) within that volume. The velocity and pressure field within a Blanked volume will be left as the initial conditions (see ).