Modelling of Cavitation Boundaries
In a cavitating flow, the boundary conditions for the flow, energy and turbulence modelling equations are the same as those in the single phase flows, described in Flow, Heat and Turbulence modules respectively. For the mass fractions of the vapor, non-condensable gas and dissolved gas, the boundary conditions for the transport equations consist of specified values and zero-gradient.
Inlet Boundary
At an inlet boundary, the inlet mass fractions of vapor, non-condensable gas and dissolved gas are all pre-determined when the corresponding transport equations are solved:
Vapor Mass Fraction: For all the model options, the vapor mass fraction should be specified at the inlet since the vapor transport equation is always solved.
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Gas Mass Fraction: The governing equation for the gas mass fraction is only solved in two models: the variable gas fraction model and the full gas model. Hence, the inlet value of 
is only required in those two model options:
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Dissolved Gas Mass Fraction: The inlet condition of the dissolved gas mass fraction is only required for the dissolved gas model (for the equilibrium dissolved gas model, the value is determined by the equilibrium condition):
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Liquid Mass Fraction: The liquid mass fraction is obtained by the physical constraint:
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It may be noted that for the models in which the mass-fraction of the non-condensable gas is specified,
is treated as a volume condition in Simerics-MP.
Outlet/Symmetry/Wall Boundary
For all the mass fraction transport equations solved in the cavitation models (vapor, gas and dissolved gas), zero-gradient condition applies for all the outlet, symmetry, and wall boundaries, while the mass fraction for the liquid is obtained using the physical constraint:
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where the subscript “
” represents vapor, gas and dissolved gas component, respectively.
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where "
" is the outlet, symmetry and wall boundary correspondingly.