oly720man From United Kingdom, joined May 2004, 6517 posts, RR: 11 Reply 2, posted (7 months 3 weeks 5 days 18 hours ago) and read 2184 times:
I'm inclined to say that the vgs are to generate a "layer" in the flow to stop the ejected flow from the mast from smearing along the nacelle. I can't imagine any aerodynamic reason related to the mast itself.
As for the perpendicular tab, it may just be to guide the flow.
boeingfixer From Canada, joined Jul 2005, 518 posts, RR: 0 Reply 6, posted (7 months 3 weeks 17 hours ago) and read 1769 times:
Quoting HAWK21M (Reply 5): Do you have a reference to the concerned SB.
The Rolls Royce SB is RB.211-71-9088 dated 17 Dec 93.
Quoting HAWK21M (Reply 3): Makes sense....Anyone aware of the earlier breather ports not having these VGs and there after getting fitted on.
As NDWDCPGUY said, the original breather was a flush louver on the cowl panel. The SB introduced the extended breather mast to keep the oil streaking on the fan cowl to a minimum. The small vanes on this new mast have been there since day one.