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 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.

Models for NCG	Gas Mass Fraction	Vapor Mass Fraction	Dissolved Gas Mass Fraction
Constant Gas Mass Fraction	No	Yes	No
Equilibrium Dissolve Gas Model	No	Yes	No
Variable Gas Mass Fraction	Yes	Yes	No
Dissolved Gas Model	No	Yes	Yes
Full Gas Model	Yes	Yes	Yes

• 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 of 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.

Cavitation Module VC Properties	Availability	Comments
Source
Free Gas Source	Dissolved Gas Model, Equilibrium Dissolve Gas Model, Full Gas Model and Variable Gas Mass Fraction Model	Add a source or sink of the nondissolved (Free) NCG to a selected volume.
Vapor Source	All Cavitation models.	Add a vapor source or sink to a selected volume.
Dissolved Gas Source	Dissolved Gas Model and Full Gas Model	Add a source or sink of dissolved NCG to a selected volume.

The State of a volume within the Cavitation 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.

If no source has been created, the Source heading does not display. Multiple sources are numbered sequentially, such as Source 1, Source 2, Source 3, and so on. If a source is removed, the remaining sources are renumbered starting at 1.