Caution for using artificial dissipation

[dreamer2368]

This issue has been observed with SBP 3-6 scheme. Other stencil operators need investigation.

When using artificial dissipation, spurious modes are observed near the boundary stencils.

For free-space simulations where the boundaries are padded with sponge zones, these modes are suppressed.

However when using wall condition where sponge zone should not be placed, this induces a numerical instability near the boundary.

Laminar flow cases, where artificial dissipation is not needed, should never use the artificial dissipation. For turbulent flows, this needs to be investigated further.