Left-handed faces are generated when non-conformal interfaces are created
Often times, when a non-conformal interface is created, it generates left-handed
faces and negative volumes.
These left-handed faces are most appear at locations where the surfaces that are
non-conformally connected have sharp corners or contortions. At some points in
such locations, the two surfaces could actually be passing through each other. In such
a case nodes projected from one surface to another during the creation
of the non-conformal interface, connect in a reverse loop leading to left-handed faces.
To over come this problem try:
(1) Reverse the order in which the surfaces are picked inside the Grid Interfaces
panel while creating the non-conformal interface
(2) If that doesn't work, look carefully at the two surfaces involved especially
at corners and turns. Modify the mesh to make sure that the two surfaces
are not passing through each other at any point.
The left-handed faces generated can be located by creating Iso-surface
of Grid->Face-handedness. (Using iso-surfaces rather than contours is
suggested since it might not be possible to see contours of face-handedness
since these faces lie on the non-conformal interface which is not available
for plotting contours.) Once these faces are located, go to TGrid (or another
meshing software) and read in the mesh *saved before making the
non-conformal interfaces* and fix corners/contortions close to
the identified locations.