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Mixed-flow fans - The gas flow patterns these fans produce resemble a combination of axial and centrifugal patterns, although the fan wheels often appear similar to centrifugal wheels. There are various types of mixed-flow fans, including gas-tight high-pressure fans and blowers.
CFMI tested both a mixed and unmixed exhaust design at the beginning of development; [4] most variants of the engine have an unmixed exhaust nozzle. [nb 2] Only the high-power CFM56-5C, designed for the Airbus A340, has a mixed-flow exhaust nozzle. [nb 1] [53] GE and Snecma also tested the effectiveness of chevrons on reducing jet noise.
The PLF1A-2 had a 40 in diameter (100 cm) geared fan stage, produced a static thrust of 4,320 lb (1,960 kg), [44] and had a bypass ratio of 6:1. [45] The General Electric TF39 became the first production model, designed to power the Lockheed C-5 Galaxy military transport aircraft. [22] The civil General Electric CF6 engine used a derived design.
A series of (e.g. labyrinth) seals allow a small flow of bleed air to wash the turbine disc to extract heat and, at the same time, pressurize the turbine rim seal, to prevent hot gases entering the inner part of the engine. Other types of seals are hydraulic, brush, carbon etc.
The high-bypass turbofan engines used on many modern airliners is an example of a very successful and popular use of ducted fan design. The duct increases thrust efficiency by up to 90% in most cases [citation needed], in comparison to a similar-sized propeller in free air. Ducted fans are quieter, and offer good opportunities for thrust vectoring.
At the other extreme, some high bypass ratio civil turbofans control the fan working line by using a convergent-divergent nozzle with an extremely low (less than 1.01) area ratio on the bypass (or mixed exhaust) stream. At low airspeeds, such a setup causes the nozzle to act as if it had variable geometry by preventing it from choking and ...
The fan stage accelerates a large volume of air through a duct, bypassing the engine core (the actual gas turbine component of the engine), and expelling it at the rear as a jet, creating thrust. A proportion of the air that comes through the fan stage enters the engine core rather than being ducted to the rear, and is thus compressed and ...