The Mass flow boundary condition constrains the mass flowing into the domain across an inlet boundary. The mass flow can be specified in a number of ways.
where mf is the normal mass flux and
ρ is the density.
where dbc (only present in the 2D Cartesian axis system) is the boundary thickness normal to the fluid-flow domain and
m is the total mass flow rate.
where dbc (only present in the 2D component Cartesian axis system) is the boundary thickness normal to the fluid-flow domain,
ρst is the standard density, and
Qsv is the standard flow rate. The standard density is defined by one of the following equations:
where Mn is the mean molar mass of the fluid,
Vn is the standard molar volume,
pst is the standard pressure,
R is the universal molar gas constant, and
Tst is the standard temperature.
Equation 3-28 or
Equation 3-29 is also enforced for compressible and incompressible flow, respectively, ensuring that the normal component of the viscous stress and the tangential component of the velocity are zero at the boundary.