Their new line "Pure Power" engines are Geared Turbofans. A gearbox between LPT spool (N1 if my memory is correct) so that spool and spin in a more efficient range and than the fan. It utilizes a highly patented gearbox with a clever way of dealing with core vs/ fan misalignment issues, it is hard to explain, it is if the whole planetary mechanism floats in space...
Just as Copernicus and Newton said.
that sounds like it is limiting N1...unless it is actually increasing N1, that would mean a higher temp ignite I suppose for N2 or greater fuel usage to get N2 going
Since the Dual Spool method might not allow in enough air, theoretically, into the high compressor, if it is geared to spin at a faster rate than dual spool physics would allow...wont that create compressor stalls??
I forgot the bypass outlets actual name, the exhaust on the Low compressor side that allows excess air to exhaust, BLEED VALVES? P&W name for them anyways
Hmmm. gear N1 to go Faster, closer to N2 in speed...
IIRC, a GG4 N2 would top out, full throttle, no afterburner at about 12K to 13K, N1 would be 10K to 10.5K, increase that to 11K or maybe 11.5K with N2 still about 12K to 13K...you certainly get forced air!
I remember after installing one in Peru, we had bad compresor stalls, it scared me to death, I kept the peruvians from standing on the side of the engine, didnt want to see a compressor disk go flying 1/4 mile through me!
I did it for aero derivitives for power generation, power companies. Same engine, just blocked in a frame, blew exhaust on a free turbine connected to a generator, think of a windmill