I searched the SW pdf files for RFF, nothing comes up.
Searching for 'Rotating', I found the below on page 223 in the Tutorial.pdf.
Relative to rotating frame. When the Relative to rotating frame option is selected, the
specified velocity (Mach number) is assumed to be relative to the rotating reference
Here, r is the distance from the rotation axis and ω is the angular velocity of the
rotating frame. The mass or volume flow rate specified in the rotating reference frame
(the Relative to rotating frame option is selected) will be the same in the absolute
(non-rotating) frame of reference if the tangential velocity component is perpendicular
to the opening’s normal, thus not influencing the mass (volume) flow rate value, e.g.
when the opening's normal coincides with the rotation axis.
I think it's a typo in 2009. I checked in 2007 it shows up as X-velocity RRF (rotating reference frame) but somehow in 2009 it is listed as RFF instead of RRF.
Thanks, I didn't want to be wondering about that all weekend