7.3.9 Pressure Far-Field Boundary Conditions

Pressure far-field conditions are used in ANSYS FLUENT to model a free-stream condition at infinity, with free-stream Mach number and static conditions being specified. The pressure far-field boundary condition is often called a characteristic boundary condition, since it uses characteristic information (Riemann invariants) to determine the flow variables at the boundaries.

Limitations

Note the following limitations and restrictions when using pressure far-field boundary conditions:

• This boundary condition is applicable only when the density is calculated using the ideal-gas law (see Section  8.3). Using it for other flows is not permitted. To effectively approximate true infinite-extent conditions, you must place the far-field boundary far enough from the object of interest. For example, in lifting airfoil calculations, it is not uncommon for the far-field boundary to be a circle with a radius of 20 chord lengths.

• It is incompatible with the multiphase models (VOF, mixture, and Eulerian) that are available with the pressure-based solver.

• It cannot be applied to flows that employ constant density, the real gas model, and the wet steam model, which are available in the density-based solver.

For an overview of flow boundaries, see Section  7.3.1.