| Geared turbofan | |
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| Geared turbofan. [1]: Fan. [2]: Gearbox. |
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. The drawback is that it increases weight and adds complexity.
In a conventional turbofan, a single shaft (the "low-pressure" or LP shaft) connects the fan, the low-pressure compressor and the low-pressure turbine (a second concentric shaft connects the high-pressure compressor and high-pressure turbine). In this configuration, the maximum tip speed for the larger radius fan limits the rotational speed for the LP shaft and thus the LP compressor and turbine. At high bypass ratios (and thus also high radius ratios) the rotational speed of the LP turbine and compressor must be relatively low, which means extra compressor and turbine stages are required to keep the average stage loadings and, therefore, overall component efficiencies to an acceptable level.
In a geared turbofan, a planetary reduction gearbox between the fan and the LP shaft allows the latter to run at a higher rotational speed thus enabling fewer stages to be used in both the LP turbine and the LP compressor, increasing efficiency and reducing weight. However, some energy will be lost as heat in the gear mechanism and weight saved on turbine and compressor stages is partly offset by that of the gearbox. There are manufacturing cost and reliability implications as well.
The lower fan speed allows higher bypass ratios, leading to reduced fuel consumption and much reduced noise. The BAe 146 is fitted with geared turbofans and is still one of the quietest commercial aircraft. [1] A large part of the noise reduction is due to reduced fan tip speeds. In conventional turbofans the fan tips exceed the speed of sound causing a characteristic drone, requiring sound deadening. Geared turbofans operate the fan at sufficiently low rotational speed to avoid supersonic tip speeds. [2]
The first geared turbofan engine was created in 1970. [3]
After considering a geared design, General Electric and Safran decided against it for their CFM LEAP due to weight and reliability concerns, postponing its use for a future application, when Pratt & Whitney began development of the geared PW1000G. [4]
Since its inception in 2016, while the durability of the geared turbofan engine of Pratt & Whitney PW1000G family has been an ongoing issue, no reliability issues are connected to the geared design. [5]
Rolls-Royce's latest engine design for large turbofans (25,000lb to 110,000lb thrust), the UltraFan [6] includes a Powergear rated at a new high of 64MW (87,000hp) and has demonstrated this full power during testing in 2021. [7]
Geared turbofans are used in the following engines:
Related lists
A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a combination of the preceding generation engine technology of the turbojet, and a reference to the additional fan stage added. It consists of a gas turbine engine which achieves mechanical energy from combustion, and a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.
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. 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 PW6000 is a high-bypass turbofan jet engine designed for the Airbus A318 with a design thrust range of 18,000–24,000 lbf (80–107 kN).
The IAE V2500 is a two-shaft high-bypass turbofan engine built by International Aero Engines (IAE) which powers the Airbus A320 family, the McDonnell Douglas MD-90, and the Embraer C-390 Millennium.
The Europrop International TP400-D6 is an 11,000 shp (8,200 kW) powerplant, developed and produced by Europrop International for the Airbus A400M Atlas military transport aircraft. The TP400 is the most powerful turboprop in service using a single propeller; only the Kuznetsov NK-12 from Russia and Progress D-27 from Ukraine, using contra-rotating propellers, is larger.
The Rolls-Royce BR700 is a family of turbofan engines for regional jets and corporate jets. It is manufactured in Dahlewitz, Germany, by Rolls-Royce Deutschland: this was initially a joint venture of BMW and Rolls-Royce plc established in 1990 to develop this engine. The BR710 first ran in 1995. The United States military designation for the BR725 variant is F130.
The Rolls-Royce RB.183 Tay is a medium-bypass turbofan engine, developed from the RB.183 Mk 555 Spey core and using a fan scaled directly from the Rolls-Royce RB.211-535E4 to produce versions with a bypass ratio of 3.1:1 or greater. The IP compressor and LP turbine were designed using technology from the RB.211 programme. The engine was first run in August 1984. The Tay 650 had a new HP turbine which incorporated new technology which had been proven with the RB.211-535E4. This engine also had a new combustor for improved durability. The Tay family is used on a number of airliners and larger business jets, including the Gulfstream IV family, Fokker 70 and Fokker 100, with a later version being used to re-engine Boeing 727-100s.
IAE International Aero Engines AG is a Zürich-registered joint venture aeroengine manufacturing company.
The General Electric CJ805 is a jet engine which was developed by General Electric Aircraft Engines in the late 1950s. It was a civilian version of the J79 and differed only in detail. It was developed in two versions. The basic CJ805-3 was a turbojet and powered the Convair 880 airliner, while CJ805-23, a turbofan derivative, powered the Convair 990 Coronado variant.
The Rolls-Royce/SNECMA M45H is an Anglo-French medium bypass ratio turbofan produced specifically for the twin-engined VFW-Fokker 614 aircraft in the early 1970s.
The Garrett TFE731 is a family of geared turbofan engines commonly used on business jet aircraft. Garrett AiResearch originally designed and built the engine, which due to mergers was later produced by AlliedSignal and now Honeywell Aerospace.
The Pratt & Whitney PW1000G, also called the GTF, is a high-bypass geared turbofan engine family produced by Pratt & Whitney. After many demonstrators, the program was launched with the PW1200G on the Mitsubishi SpaceJet in March 2008, first flight tested in July 2008. The first variant to be certified was the PW1500G for the Airbus A220 in February 2013. The program cost is estimated at $10 billion.
The Lycoming ALF 502/LF 507 is a geared turbofan engine produced by Lycoming Engines, AlliedSignal, and then Honeywell Aerospace. The U.S. military designation for the ALF 502 is YF102.
The Pratt & Whitney Canada PW800 is a series of turbofan engines in the 10,000–20,000 lbf (44–89 kN) thrust class, manufactured by Pratt & Whitney Canada. Intended for the regional jet and business jet market, the gear-less PW800 shares a common core with the larger, geared PW1000G. The first variants were certified on February 15, 2015, to power the new Gulfstream G500/G600. After that it has been certified also for the Dassault Falcon 6X in 2021.
The accessory drive is a gearbox that forms part of a gas turbine engine. Although not part of the engine's core, it drives the accessories – such as generators, pumps for fuel and lubrication oil, air compressors, hydraulic pumps and engine starters – that are otherwise essential for the operation of the engine or the aircraft on which it is mounted. Accessory drives on large engines handle between 400–500 hp.
The Rolls-Royce RB.203 Trent was a British medium-bypass turbofan engine of around 10,000lb thrust designed for production in the late 1960s, bearing no relation to the earlier Rolls-Royce RB.50 Trent turboprop or the later high-bypass Rolls-Royce Trent turbofan.
The Turbomeca Aspin was a small French turbofan engine produced by Turbomeca in the early 1950s. This geared turbofan design was the first turbofan to fly, powering the Fouga Gemeaux test-bed aircraft on 2 January 1952.
The IAE V2500SF SuperFan was a design study for a high-bypass geared turbofan derived from the IAE V2500. It was offered as the primary engine option for the Airbus A340 in January 1987. Although several customers signed preliminary contracts for this variant, the International Aero Engines board decided in April 1987 to stop the development of the SuperFan, which forced Airbus to partly re-design the A340.
A variable pitch fan is similar in concept to that of a variable-pitch propeller and involves progressively reducing the pitch of the fan on a turbofan as the engine is throttled. Although variable pitch fans are used in some industrial applications, the focus of this article is on their use in turbofan engines. No production engine uses such a feature; however, it will likely be required on at least some of the next generation of high bypass ratio turbofans.
Advanced technology engine is a turbine engine that allows different turbines to spin at different, individually optimum speeds, instead of at one speed for all. It became common in the 21st century. It emerged on larger airplanes, before finding other applications.
