WIP: Penalisation method for sheath boundaries #182
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Imposes sheath boundary conditions over a complex shaped wall by using a penalty method. In practical terms we create a vacuum region by damping density, momentum and pressure to zero in specified cells. This version is very simple, just for fluid flows, and doesn't handle currents, heat diffusion, or recycling that are all needed.
Defaults to 1. This is used in the calculation of the sheath entrance velocity. Needed this for comparison to flows without heat conduction.
Checks convergence of sheath boundary and penalty method in 1D fluid flow.
Comparing evolution of pressure vs energy
Work in progress on adjusting sheath heat transmission.
Previously the damping depended on both the difference between reconstructed and cell-center velocity AND differences in density. In cases of large (supersonic) flow, depending on the density profile this numerical damping term could result in flows accelerating. By removing the dependence on the density, and just damping the velocity, this seems to avoid some sheath boundary-induced numerical instabilities.
Volumetric and surface penalty terms. Seems to be working, converging if penalty_timescale is made reasonably long (e.g. 1e-4 seconds in transport simulation test).
Trying to impose a surface current at the edge of penalty regions, by setting electron and ion flows.
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Work in progress.
Aims to apply a sheath boundary condition over an arbitrary shaped (3D) boundary that is immersed in the structured grid.