The boundary condition parameters for the Cavitation module apply to boundaries in the Flow Analysis Tree. The options also apply to interfaces for which the Cavitation module is blanked on one side of the interface, creating a Boundary.

The boundary conditions appear in the Properties panel when a boundary is selected in the Flow Analysis Tree under General Boundaries.

On a solid wall boundary, a zero-flux or gradient condition applies for the mass fractions of vapor, NCG, and dissolved gas, depending on the cavitation model that you select. No direct user inputs are required.

For a physical symmetry, a zero-flux or gradient condition applies for the mass fractions of vapor, NCG, and dissolved gas, depending on the cavitation model that you select. No direct user inputs are required.

At a flow outlet such as Specified Pressure Outlet or Resistor Capacitor, the mass fraction values are specified for the vapor, NCG, and dissolved gas, depending on the cavitation model that you select. However, the specified values are only used when back flow, which is flow entering the domain through the outlet, occurs. If the flow is required to exit the outlet, then zero-flux or gradient conditions apply.

Depending on the Cavitation model selected, the actual mass fraction inputs are listed in the following table:

At a flow inlet, Specified Velocity, Specified Volumetric Flux, Specified Total Pressure or Specified Pressure Inlet, specified values are applied for the mass fractions of vapor, NCG, and dissolved gas, depending on the cavitation model in use. If the flow has to leave the boundary, then zero-flux or gradient conditions actually apply at the inlet.

If the values for Vapor Mass Fraction, Gas Mass Fraction, and Dissolved Gas Mass Fraction are known, or the default value is acceptable, then you can use Specified Values. The inputs for specified values are mass fractions.

This is the default boundary condition when you select Specified Velocity, Specified Volumetric Flux, Specified Total Pressure, or Specified Pressure Inlet under the Flow module. Based on the Cavitation model you select, the mass fraction inputs for a boundary will change.

The mass fraction of Gas Mass Fraction, Dissolved Gas Mass Fraction, and Vapor Mass Fraction for any fluid exiting the domain is based on their respective internal (upwind) mass fraction. For any fluid entering the domain, mass fraction is based on the value specified for the selected boundary. The mass fraction of the above specified at the outlet can influence the internal mass fraction through diffusion. Typically, this effect is insignificant unless the outflow is very small or the conductivity is very high.

For a fluid-solid interface which is blanked on one side in the Flow module, it is treated as a wall boundary for the flow. Zero-flux or gradient conditions apply for the mass fractions of vapor, NCG, and dissolved gas, depending on the cavitation model that you use. For a fluid-fluid interface, it is then considered as face connection between interior cells, and no boundary conditions are required.