Vaggelis Papoutsis authored Jul 19, 2023 and Andrew Heather committed Dec 18, 2023

Both porosity-based and level-set-based topO frameworks are included
through the topO and levelSet designVariables, respectively.

Both frameworks work by manipulating an underlying field of design
variables, defined in all cells of the computational domain. That field
is then regularised through a Helmholtz-like filter, before being
processed in a different way from the two topO frameworks (the
porosity-based topO sharpens/projects it while the level-set-based topO
computes signed distances around its zero iso-surface). The result of
this processing is then fed into functions that define source terms to
be added to the mean flow and turbulence model equations, to block
off/solidify parts of the mesh that are counterproductive with respect
to the objective function. These source terms are added through
fvOptions.

Since the designed walls are only simulated through source terms, the
outcome of topO should be re-analyzed on a body-fitted grid, to quantify
the actual gain in the objective function. Both topO frameworks output
the designed wall in STL format which can be used, for instance with
snappyHexMesh, to construct such a body fitted grid.