Boundary velocity images

Symmetry and viscous-wall boundary conditions build ghost velocities from simple linear images of the interior state.

Symmetry (reflection)

With unit face normal \(\mathbf{n}\) and face speed \(v_{fn}\):

\[v_n^{\mathrm{rel}} = \mathbf{n}\cdot\mathbf{v} - v_{fn}\]

\[\mathbf{v}' = \mathbf{v} - 2\,\mathbf{n}\,v_n^{\mathrm{rel}}\]

\[\mathbf{v}' = -\mathbf{v} + 2\,\mathbf{v}_{\mathrm{wall}}\]

Face primitive average for the symmetry face state is the arithmetic mean of interior and reflected states.

Blazek, J. Computational Fluid Dynamics: Principles and Applications (symmetry / wall boundary treatment).
See references.rst for the citation policy.

Pure APIs: NsBcPolicy.h. Tests: bc_policy_test.