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A turbofan does this by transferring energy available inside the engine, from the gas generator, to a ducted fan which produces a second, additional mass of accelerated air. The transfer of energy from the core to bypass air results in lower pressure and temperature gas entering the core nozzle (lower exhaust velocity), and fan-produced higher ...
The geared turbofan is a type of turbofan aircraft engine with a planetary gearbox between the low pressure compressor / turbine and the fan, enabling each to spin at its optimum speed. The benefit of the design is lower fuel consumption and much quieter operation.
While a turbojet engine uses all of the engine's output to produce thrust in the form of a hot high-velocity exhaust gas jet, a turbofan's cool low-velocity bypass air yields between 30% and 70% of the total thrust produced by a turbofan system. [80] The net thrust (F N) generated by a turbofan can also be expanded as: [81]
The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. [1] A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core.
The Pratt & Whitney F100 (company designation JTF22 [1]) is a low bypass afterburning turbofan engine. It was designed and manufactured by Pratt & Whitney to power the U.S. Air Force's "FX" initiative in 1965, which became the F-15 Eagle.
In a military turbofan combat engine, the bypass air is added into the exhaust, thereby increasing the core and afterburner efficiency. In turbojets the gain is limited to 50%, whereas in a turbofan it depends on the bypass ratio and can be as much as 70%.
A turbofan typically has extra turbine stages to turn the fan. Turbofans were among the first engines to use multiple spools—concentric shafts that are free to rotate at their own speed—to let the engine react more quickly to changing power requirements. Turbofans are coarsely split into low-bypass and high-bypass categories.
The General Electric CF34 is a civilian high-bypass turbofan developed by GE Aviation from its TF34 military engine. The CF34 is used on a number of business and regional jets, including the Bombardier CRJ series, the Embraer E-Jets, and Comac ARJ21. [2] [3] In 2012, there were 5,600 engines in service.