A new family of interface compression interpolation schemes based on
piecewise-linear interface calculation (PLIC). PLIC represents an interface by
surface-cuts which split each cell to match the volume fraction of the phase in
that cell. The surface-cuts are oriented according to the point field of the
local phase fraction. The phase fraction on each cell face — the interpolated
value — is then calculated from the amount submerged below the surface-cut.
The basic PLIC method generates a single cut so cannot handle cells in which
there are multiple interfaces or where the interface is not fully resolved. In
those cells, the interpolation reverts to an alternative scheme, typically
standard interface compression. PLIC, with a fallback to interface compression,
produces robust solutions for real engineering cases. It can run with large time
steps so can solve problems like hydrodynamics of a planing hull, with rigid
body motion of the hull (above). The user selects PLIC by the following setting
in fvSchemes:
div(phi,alpha) Gauss PLIC interfaceCompression vanLeer 1;
The multicut PLIC (MPLIC) scheme extends PLIC to handle multiple
surface-cuts. Where a single cut is insufficient, MPLIC performs a topological
face-edge-face walk to produce multiple splits of a cell. If that is still
insufficient, MPLIC decomposes the cell into tetrahedrons on which the cuts are
applied. The extra cutting carries an additional computational cost but requires
no fallback. The user selects MPLIC by the following setting in the fvSchemes
file:
div(phi,alpha) Gauss MPLIC;
Variants of the PLIC and MPLIC schemes are also available which use velocities
at the face points to calculate the face flux. These PLICU and MPLICU schemes
are likely to be more accurate in regions of interface under high shear.
More details can be found here:
https://cfd.direct/openfoam/free-software/multiphase-interface-capturing
Jakub Knir
CFD Direct Ltd.
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