Issues with mixed walls in mfix-24.1


Is there a way to use a partial slip for TFM, like Jenkins or JJ for the solid phase and no-slip for the fluid on boundaries that were defined using cutcell (and stl)? I have not managed it from the GUI and forced it from the *mfx leads to an error telling me cartesian grid cannot be used with JJ…

Hi @ebreard6 Sorry this question slipped between the cracks. Typically the GUI tries to keep users from selecting invalid combinations of options. As you found by forcing BC_JJ_PS in the file, Cartesian grid is not compatible with this option. Here’s the relevant section from the MFiX spec:

Enable Jackson-Johnson partial slip boundary

  • Disabled for DEM and PIC solids
  • Disabled (0.0) for CARTESIAN_GRID = .TRUE.
  • Disabled (0.0) for KT_TYPE = ‘ALGEBRAIC’
  • Disabled (0.0) for KT_TYPE = ‘GHD’
  • Sets keyword BC_JJ_PS(#)
  • DEFAULT 1.0 when not disabled
  • Unsets keyword BC_Hw_s(#,#) to UNDEFINED
  • Sets keyword BC_Uw_s(#,#) to 0.0
  • Sets keyword BC_Vw_s(#,#) to 0.0
  • Sets keyword BC_Ww_s(#,#) to 0.0
  • Enables wall velocity specification (below)
  • Disables transfer coefficient specification (below)

If you believe there is a bug in the implementation of this spec, please let us know.

– Charles