Originally added for a simple Gaede pump modelling, Molflow can treat certain facets as "Moving parts", and add a certain velocity vector to the normal rebounce directions of molecules hitting a facet. The velocity vector itself can be set globally through the Tools/Moving parts menu:

Here we can define either a fixed velocity vector, or one that is calculated locally for each collision (rotation):

Once the global parameter is defined, we can select individual facets as "moving" by ticking the chackbox in the advanced facet parameters pane:

An example application is the aforementioned Gaede pump where the rotor is modelled as a disc consisting of "moving" facets. We can see its effect thorugh the pressure and direction textures:

Note1: Adding a velocity vector that is much higher than the original molecule velocity might substantially change the rebounce direction, even turning rebounded particle against the facet in some cases, creating leaks.

Note2: The special "velocity" profiles, that show the speed distribution of impinging molecules on a facet are divided to 100 different values between 0...4*v_prob, where v_prob is the most probablt molecule velocity for the facet's temperature. If adding a large velocity vector, these profiles might be "out of scale" - a transparent counter facet with adjusted temperature might help.