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Initial Condition and State
Initial Condition and State
In the Flow Analysis Tree, under Domains, select a fluid domain to see the Initial Condition and State in the Properties panel.
Initial Condition
Initial Condition refers to the values of the independent variables required to start a simulation when you select Start from Initial Values in the Run group. For the Flow module, you can specify the initial Velocity and Pressure fields for each Volume.
You can specify the Initial Condition for a rotating volume (Rotating System) or nonrotating volume (Specified Values). Use global expressions to set the initial specified values for pressure and velocity.
Specified Values—Specifies the initial velocity and pressure field for a selected nonrotating volume.
Rotating System—Specifies the initial velocity and pressure field for a selected rotating volume. Rotating System is defined using the following: Pressure, Rotational Units, 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 Component sometimes improves convergence for Steady state solution and is the default for Steady state solution instead of 0. This default should have no impact on the final solution. However, for the sake of convergence, initial conditions should be as close to the solution as possible.
For a Transient solution, the initial Axial Velocity Component represents the axial velocity at time equals zero and the initial conditions represent the Flow and Pressure fields at time equals zero. After a Transient solution achieves steady or periodic conditions, the initial conditions have no impact on the solution. However, prior to achieving steady or periodic conditions, the initial conditions impact the solution and should represent physical values at time equals zero or be as close to the final solution as possible.
If the State of the volume is set to Blanked, the value of the axial velocity in the volume is frozen to the initial Axial Velocity Component. This may be incorrect if the value does not correspond to what would be physically realistic, such as if the default of 0.1 m/s axial velocity is displayed in a solid.
State
The State of a volume within the Flow module determines whether Velocity and Pressure are solved (Active) or not solved (Blanked) within that volume. The Velocity and Pressure field within a Blanked volume is left at the initial condition.