The Interior Flux/Source boundary condition, which is only available for interior boundaries in the Stabilized Convection-Diffusion Equation interface, adds a flux or source g on the downside and upside of an interior boundary:

The g term may contain a general expression of the dependent variables. The q coefficients simplify the implementation of a Robin boundary condition by including a term on the form qu, where u is the dependent variable.

The red arrows in the Graphics window point toward the downside from the upside.

By default, all check boxes are selected for the Diffusive flux, Conservative convective flux, and Nonconservative convective flux to include all flux components. You can use the Interior Flux/Source boundary condition in the Stabilized Convection-Diffusion Equation interface as an outflow condition (from a domain) by clearing the Nonconservative convective flux and Conservative convective flux check boxes and as a supersonic outflow condition (from a domain) by clearing all check boxes so that the flux is computed from inside the domain.

Enter values or expressions for the values of the boundary flux or source g on the downside and upside in the associated text fields for gd and gu under Downside and Upside, respectively.

Enter values or expressions for the values of the coefficient q and the components of the vector k on the downside and upside in the corresponding text fields under Downside and Upside, respectively. The addition of the qu terms to the boundary flux or source can represent absorption or impedance at the boundary.