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 is a volume condition in the Multiphase module that refers to selected volumes. Initial Condition refers to the values of the independent variables that are used to start a simulation when you select Start from Initial Values in the Run group. Alternatively, you can also use Start from Solution or continuation run to start a simulation. In such cases, the initial condition values that were set under the volume are not used.
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 volume fraction of a selected component in a selected volume. The sum of the value of the initial volume fractions for all components in a volume should add to one. You can also use Expression Editor to set the initial specified value of the volume fraction.
Use Specified Values to specify the initial velocity and pressure 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.
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.
For a Transient solution, the initial Axial Velocity Component represents the axial velocity 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.
Source
When you create a source for the mixture under the Flow module, the possible sources are momentum source and mass source.
When you create a source for the mixture under the Heat module, the possible sources are Heat Source Per Volume and Total Heat Source.
State
The State of a volume within the Multiphase 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.