8 – Boundary conditions (Fictitious volumes)

The CFD Studio software uses fictitious volumes at the boundary conditions, as shown in figure (8.1). These volumes do not belong to the physical domain of our problem. We use this technique to facilitate the discretization of general conservation equation. The fictitious volumes are used in such a way that all elemental volumes, even that which belong to boundaries, can be handled as internal volumes.



Figure 8.1 – Calculation domain.
When we are using fictitious volumes, we should create equations for these volumes, which are related to the boundary conditions. It is natural writing these equations in the same way as we have written them for internal volumes:

 
                   (8.1)
The boundary conditions that may be found in csfl-lib-1.0 are:
  • Thermal conditions:

    • Prescribed temperature;
    • Prescribed flux;
    • Convection.
  • Flow conditions:

    • Prescribed velocities (u e v);
    • Outlet condition;
    • Symmetry condition.
Below, we have the equations and a detailed explanation for all boundary conditions using fictitious volumes.
 
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