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The Geared turbofan
is a type of turbofan
airplane engine, similar to a turbojet
. It consists of a geared ducted fan
with a smaller diameter turbojet engine mounted behind it that powers the fan. Typical of this configuration are the long-established Honeywell TFE731
, the Honeywell ALF 502
/507, and the recent Pratt & Whitney PW1000G
A small part of the airstream passes through the core of the engine, which includes compressors, a combustion chamber and turbines. All of these comprise the "turbojet" mentioned in the first paragraph. The core turbines drive the compressors and the fan.
As bypass ratio increases, the mean radius ratio of the fan and LP turbine increases. Consequently, if the fan is to rotate at its optimum blade speed the LP turbine blading will spin slowly, so additional LPT stages will be required, to extract sufficient energy to drive the fan. Introducing a reduction gearbox
, with a suitable gear ratio, between the LP shaft and the fan enables both the fan and LP turbine to operate at their optimum speeds.
In a Geared Turbofan, the fan that produces most of the thrust is driven through a reduction gearbox, rather than being directly connected to the rest of the engine. The gearbox between the fan and low-pressure compressor and turbine allows the selection of the best possible operating speed for each engine section.... Read More