Turbofan engine operation

The spool 14 supports a turbine 18 and is housed within a core nacelle A fan 20 is coupled to the spool 14 and includes a target operability line.

Turbofan engine operation

Core nozzle Fan nozzle Schematic diagram illustrating a 2-spool, Turbofan engine operation turbofan engine with an unmixed exhaust. The low-pressure spool is coloured green and the high-pressure one purple.

Again, the fan and booster stages are driven by the low-pressure turbine, but more stages are required.

A mixed exhaust is often employed nowadays. To boost fuel economy and reduce noise, almost all of today's jet airliners and most military transport aircraft e.

Modern combat aircraft tend to use low-bypass ratio turbofans, and some military transport aircraft use turboprops. Low specific thrust is achieved by replacing the multi-stage fan with a single-stage unit. Unlike some military engines, modern civil turbofans lack stationary inlet guide vanes in front of the fan rotor.

The fan is scaled to achieve the desired net thrust. The core or gas generator of the engine must generate enough power to drive the fan at its design flow and pressure ratio. Reducing the core mass flow tends to increase the load on the LP turbine, so this unit may require additional stages to reduce the average stage loading and to maintain LP turbine efficiency.

Reducing core flow also increases bypass ratio. Bypass ratios greater than 5: Further improvements in core thermal efficiency can be achieved by raising the overall pressure ratio of the core. Improved blade aerodynamics reduces the number of extra compressor stages required.

With multiple compressors i. The lower the specific thrust of a turbofan, the lower the mean jet outlet velocity, which in turn translates into a high thrust lapse rate i. See technical discussion below, item 2. Consequently, an engine sized to propel an aircraft at high subsonic flight speed e.

Low specific thrust engines tend to have a high bypass ratio, but this is also a function of the temperature of the turbine system. The turbofans on twin engined airliners are further more powerful to cope with losing one engine during take-off, which reduces the aircraft's net thrust by half.

Modern twin engined airliners normally climb very steeply immediately after take-off. If one engine is lost, the climb-out is much shallower, but sufficient to clear obstacles in the flightpath.

The Soviet Union's engine technology was less advanced than the West's and its first wide-body aircraft, the Ilyushin Ilwas powered by low-bypass engines.

Turbofan engine operation

The Yakovlev Yaka medium-range, rear-engined aircraft seating up to passengers introduced in was the first Soviet aircraft to use high-bypass engines. Turbofan configurations[ edit ] Turbofan engines come in a variety of engine configurations. For a given engine cycle i.

Off-design performance and stability is, however, affected by engine configuration. As the design overall pressure ratio of an engine cycle increases, it becomes more difficult to operate at low rpm, without encountering an instability known as compressor surge.

This occurs when some of the compressor aerofoils stall like the wings of an aircraft causing a violent change in the direction of the airflow. However, compressor stall can be avoided, at low rpm, by progressively: As the HP compressor has a modest pressure ratio its speed can be reduced surge-free, without employing variable geometry.

However, because a shallow IP compressor working line is inevitable, the IPC has one stage of variable geometry on all variants except thewhich has none.

Despite the simplicity of the turbomachinery configuration, the M53 requires a variable area mixer to facilitate part-throttle operation.

Turbofan engine operation

Hot gas from the turbojet turbine exhaust expanded through the LP turbine, the fan blades being a radial extension of the turbine blades. One of the problems with the aft fan configuration is hot gas leakage from the LP turbine to the fan.

The Low Pressure spool runs at a lower radial velocity. The High Pressure spool turns more quickly and its compressor further compresses part of the air for combustion. At the smaller thrust sizes, instead of all-axial blading, the HP compressor configuration may be axial-centrifugal e.

Boosted two-spool[ edit ] Higher overall pressure ratios can be achieved by either raising the HP compressor pressure ratio or adding an intermediate-pressure IP compressor between the fan and HP compressor, to supercharge or boost the latter unit helping to raise the overall pressure ratio of the engine cycle to the very high levels employed today i.

All of the large American turbofans e. The high bypass ratios i. Three-spool[ edit ] Rolls-Royce chose a three-spool configuration for their large civil turbofans i. The first three-spool engine was the earlier Rolls-Royce RB. Geared turbofan Geared turbofan As bypass ratio increases, the mean radius ratio of the fan and low-pressure turbine LPT increases.Jet engines, which are also called gas turbines, work by sucking air into the front of the engine using a fan.

From there, the engine compresses the air, mixes fuel with it, ignites the fuel/air mixture, and shoots it out the back of the engine, creating thrust. The turbofan engine according to claim 1, wherein the target operability line is near a stall/flutter boundary of the turbofan.

3. The turbofan engine according to claim 1, comprising an airspeed sensor in communication with the controller for providing an aircraft airspeed.

English: Schematic diagram illustrating the operation of a 2-spool, high-bypass turbofan engine, with LP spool in green and HP spool in purple.

Polski: Schematyczny diagram pracy uogólnionego silnika turbowentylatorowego wysokoprzepływowego. May 05,  · A turbofan engine is the most modern variation of the basic gas turbine engine.

As with other gas turbines, there is a core engine, whose parts and operation are discussed on a separate page. In the turbofan engine, the core engine is surrounded by . The turbofan engine according to claim 1, wherein the target operability line is near a stall/flutter boundary of the turbofan.

3. The turbofan engine according to claim 1, comprising an airspeed sensor in communication with the controller for providing an aircraft airspeed. English: Schematic diagram illustrating the operation of a 2-spool, high-bypass turbofan engine, with LP spool in green and HP spool in purple.

Polski: Schematyczny diagram pracy uogólnionego silnika turbowentylatorowego wysokoprzepływowego.

USA1 - Turbofan engine operation control - Google Patents