turbofan engine
-
Upload
andrea-albanese -
Category
Documents
-
view
27 -
download
1
description
Transcript of turbofan engine
-
5/20/2018 turbofan engine
1/47
Turbofan
Turbofan Engine
A turbofanis a type of aircraft engineconsisting of a ducted fanwhich is
powered by a gas turbine. Part of the airstream from the ducted fan passes
through the gas turbine core, providing oxygen to burn fuel to create
power. However, most of the air flow bypasses the engine core, and is
accelerated by the fan blades in much the same manner as apropeller.
The combination of thrust produced from the fan and the exhaust fromthe core is a more efficient process than otherjet enginedesigns, resulting
in a comparatively low specific fuel consumption.[!
A few designs wor" slightly differently and have the fan blades as a radial
extension of an aft#mounted low#pressure turbine unit.
Turbofans have a net exhaust speed that is much lower than a turbojet.
This ma"es them much more efficient at subsonic speeds than turbojets,
and somewhat more efficient at supersonic speeds up to
roughly $ach.%, but have also been found to be efficient when used
with continuous afterburnerat $ach & and above.
All of the jet engines used in currently manufactured commercial jet
aircraft are turbofans. They are used commercially mainly because they
are highly efficient and relatively 'uiet in operation. Turbofans are also
used in many military jet aircraft.
http://en.wikipedia.org/wiki/Aircraft_enginehttp://en.wikipedia.org/wiki/Ducted_fanhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Propellerhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Turbofan#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Afterburnerhttp://en.wikipedia.org/wiki/Aircraft_enginehttp://en.wikipedia.org/wiki/Ducted_fanhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Propellerhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Turbofan#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Afterburner -
5/20/2018 turbofan engine
2/47
Turbofan
Turbofan
(chematic diagram of a high#bypass turbofan engine
A turbofanis a type of aircraft engineconsisting of a ducted fanwhich is
powered by a gas turbine. Part of the airstream from the ducted fan passes
through the gas turbine core, providing oxygen to burn fuel to create
power. However, most of the air flow bypasses the engine core, and is
accelerated by the fan blades in much the same manner as apropeller.
The combination of thrust produced from the fan and the exhaust fromthe core is a more efficient process than otherjet enginedesigns, resulting
in a comparatively low specific fuel consumption.[!
A few designs wor" slightly differently and have the fan blades as a radial
extension of an aft#mounted low#pressure turbine unit.
Turbofans have a net exhaust speed that is much lower than a turbojet.
This ma"es them much more efficient at subsonic speeds than turbojets,
and somewhat more efficient at supersonic speeds up to
roughly $ach.%, but have also been found to be efficient when usedwith continuous afterburnerat $ach & and above.
)
http://en.wikipedia.org/wiki/Aircraft_enginehttp://en.wikipedia.org/wiki/Ducted_fanhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Propellerhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Turbofan#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Afterburnerhttp://en.wikipedia.org/wiki/File:Turbofan_operation.svghttp://en.wikipedia.org/wiki/Aircraft_enginehttp://en.wikipedia.org/wiki/Ducted_fanhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Propellerhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Turbofan#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Afterburner -
5/20/2018 turbofan engine
3/47
Turbofan
All of the jet engines used in currently manufactured commercial jet
aircraft are turbofans. They are used commercially mainly because they
are highly efficient and relatively 'uiet in operation. Turbofans are alsoused in many military jet aircraft.
To move an airplanethrough the air, thrustis generated by some "ind
ofpropulsion system. $ost modern airliners useturbofanengines
because of their high thrust and good fuel efficiency.*n this page, we
will discuss some of the fundamentals of turbofan engines.
A turbofan engine is the most modern variation of the basic gasturbineengine. As with other gas turbines, there is a core engine,
whosepartsand operation are discussed on a separate page. +n the
turbofan engine, the core engine is surrounded by a fan in the front and an
additional turbine at the rear. The fan and fan turbine are composed of
many blades, li"e the corecompressorand core turbine,and are connected
to an additional shaft. All of this additional turbomachineryis colored
green on the schematic.As with the core compressor and turbine, some of
the fan blades turn with the shaft and some blades remain stationary. The
fan shaft passes through the core shaft for mechanical reasons. This type
of arrangement is called a two spoolengine one -spool- for the fan, one
-spool- for the core. (ome advanced engines have additional spools for
even higher efficiency.
How does a turbofan engine work?
The incoming air is captured by the engine inlet. (ome of the incoming
air passes through the fan and continues on into the core compressor and
then theburner,where it is mixed with fuel and combustionoccurs. The
hot exhaust passes through the core and fan turbines and then out
the no//le,as in a basic turbojet.The rest of the incoming air passes
through the fan and bypasses, or goes around the engine, just li"e the air
through apropeller.The air that goes through the fan has a velocity that is
slightly increased from free stream. (o a turbofan gets some of its thrust
from the core and some of its thrust from the fan. The ratio of the air that
&
http://www.grc.nasa.gov/WWW/K-12/airplane/airplane.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/bgp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/sfc.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/Animation/turbtyp/etcs.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbdraw.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inlet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burner.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/combst1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/nozzle.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbj.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/airplane.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/bgp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/sfc.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/Animation/turbtyp/etcs.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbdraw.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inlet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burner.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/combst1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/nozzle.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbj.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propth.html -
5/20/2018 turbofan engine
4/47
Turbofan
goes around the engine to the air that goes through the core is called
the bypass ratio.
0ecause the fuel flow rate for the core is changed only a small amount by
the addition of the fan, a turbofan generates more thrust for nearly thesame amount of fuel used by the core. This means that a turbofan is very
fuel efficient. +n fact, high bypass ratio turbofans are nearly as fuel
efficient as turboprops. 0ecause the fan is enclosed by the inlet and is
composed of many blades, it can operate efficiently at higher speeds than
a simple propeller. That is why turbofans are found on high speed
transports and propellers are used on low speed transports. 1ow bypass
ratio turbofans are still more fuel efficient than basic turbojets. $any
modern fighter planes actually use low bypass ratio turbofans e'uipped
with afterburners.They can then cruise efficiently but still have high
thrust when dogfighting. 2ven though the fighter plane can fly much
faster than the speed of sound, the air going into the engine must travel
less than the speed of sound for high efficiency. Therefore, the airplane
inlet slows the air down from supersonic speeds.
Early turbofans
2arly turbojet engines were very fuel#inefficient, as their overall pressureratio and turbine inlet temperature were severely limited by the
technology available at the time. The very first running turbofan was the
3erman4aimler#0en/ 40 %56a"a 67#665 which was operated on its
testbed on April , 78&. The engine was abandoned later while the war
went on and problems could not be solved. The 0ritish
wartime $etrovic" 9.)axial flow jet was given a fan to create the first
0ritish turbofan.
+mproved materials, and the introduction of twin compressors such as inthe Pratt : ;hitney high
velocity exhaust better suited to supersonic flight.
The original low-bypass turbofanengines were designed to improve
propulsive efficiency by reducing the exhaust velocity to a value closer to
that of the aircraft. The ?olls#?oyce =onway, the first production
turbofan, had a bypass ratio of 6.&, similar to the modern 3eneral 2lectric9868fighter engine. =ivilian turbofan engines of the 7%6s, such as
8
http://www.grc.nasa.gov/WWW/K-12/airplane/aturbp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturba.htmlhttp://en.wikipedia.org/w/index.php?title=Daimler-Benz_DB_670&action=edit&redlink=1http://en.wikipedia.org/wiki/Metrovick_F.2http://en.wikipedia.org/wiki/Pratt_%26_Whitney_JT3Chttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Rolls-Royce_Conwayhttp://en.wikipedia.org/wiki/General_Electric_F404http://en.wikipedia.org/wiki/General_Electric_F404http://www.grc.nasa.gov/WWW/K-12/airplane/aturbp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturba.htmlhttp://en.wikipedia.org/w/index.php?title=Daimler-Benz_DB_670&action=edit&redlink=1http://en.wikipedia.org/wiki/Metrovick_F.2http://en.wikipedia.org/wiki/Pratt_%26_Whitney_JT3Chttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Rolls-Royce_Conwayhttp://en.wikipedia.org/wiki/General_Electric_F404http://en.wikipedia.org/wiki/General_Electric_F404 -
5/20/2018 turbofan engine
5/47
Turbofan
the Pratt : ;hitney
-
5/20/2018 turbofan engine
6/47
Turbofan
introduced if the turbine inlet temperature is allowed to increase, to
compensate for a correspondingly smaller core flow. +mprovements in
turbine cooling>material technology would facilitate the use of a higher
turbine inlet temperature, despite increases in cooling air temperature,
resulting from a probable increase in overall pressure ratio.
2fficiently done, the resulting turbofan would probably operate at a
higher no//le pressure ratio than the turbojet, but with a lower exhaust
temperature to retain net thrust. (ince the temperature rise across the
whole engine inta"e to no//le would be lower, the dry power fuel flow
would also be reduced, resulting in a better specific fuel
consumption(9=.
A few low#bypass ratio military turbofans e.g. 9868 have Dariable +nlet3uide Danes, with piano#style hinges, to direct air onto the first rotor
stage. This improves the fan surge margin see compressor map in the
mid#flow range. The swing wing 9#achieved a very high range >
payload capability by pioneering the use of this engine, and it was also
the heart of the famous 9#8 Tomcatair superiority fighter which used the
same engines in a smaller, more agile airframe to achieve efficient cruise
and $ach ) speed.
Afterburning turbofans
(ince the 756s, mostjet fighterengines have been low>medium bypass
turbofans with a mixed exhaust, afterburnerand variable area final
no//le. An afterburner is a combustor located downstream of the turbine
blades and directly upstream of the no//le, which burns fuel from
afterburner#specific fuel injectors. ;hen lit, prodigious amounts of fuel
are burnt in the afterburner, raising the temperature of exhaust gases by a
significant amount, resulting in a higher exhaust velocity>engine specific
thrust. The variable geometry no//le must open to a larger throat area to
accommodate the extra volume flow when the afterburner is lit.
Afterburning is often designed to give a significant thrust boost for ta"e
off, transonic acceleration and combat maneuvers, but is very fuel
intensive. =onse'uently afterburning can only be used for short portions
of a mission. However the $ach & (?#5was designed for continuous
operation and to be efficient with the afterburner lit.
Enli"e the main combustor, where the downstream turbine blades must
not be damaged by high temperatures, an afterburner can operate at the
%
http://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Compressor_maphttp://en.wikipedia.org/wiki/F-111http://en.wikipedia.org/wiki/F-14_Tomcathttp://en.wikipedia.org/wiki/Jet_fighterhttp://en.wikipedia.org/wiki/Afterburnerhttp://en.wikipedia.org/wiki/SR-71http://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Specific_fuel_consumptionhttp://en.wikipedia.org/wiki/Compressor_maphttp://en.wikipedia.org/wiki/F-111http://en.wikipedia.org/wiki/F-14_Tomcathttp://en.wikipedia.org/wiki/Jet_fighterhttp://en.wikipedia.org/wiki/Afterburnerhttp://en.wikipedia.org/wiki/SR-71 -
5/20/2018 turbofan engine
7/47
Turbofan
ideal maximum stoichiometric temperature i.e. about
)66F>&5@6?a>&&)69. At a fixed total applied fuelGair ratio, the total
fuel flow for a given fan airflow will be the same, regardless of the dry
specific thrust of the engine. However, a high specific thrust turbofan
will, by definition, have a higher no//le pressure ratio, resulting in a
higher afterburning net thrust and, therefore, a lower afterburning specific
fuel consumption. However, high specific thrust engines have a high dry
(9=. The situation is reversed for a medium specific thrust afterburning
turbofanG i.e. poor afterburning (9=>good dry (9=. The former engine is
suitable for a combat aircraft which must remain in afterburning combat
for a fairly long period, but only has to fight fairly close to the airfield
e.g. cross border s"irmishes The latter engine is better for an aircraft
that has to fly some distance, or loiter for a long time, before going intocombat. However, the pilot can only afford to stay in afterburning for a
short period, before his>her fuel reserves become dangerously low.
$odern low#bypass military turbofans include the Pratt : ;hitney 97,
the 2urojet 2Turbomeca
Adourafterburning in the (2P2=AT
-
5/20/2018 turbofan engine
8/47
Turbofan
2. Fan
3. Low pressure compressor
4. High pressure compressor
. Com!ustion cham!er
". High pressure tur!ine#. Low pressure tur!ine
$. Core no%%le
&. Fan no%%le
(chematic diagram illustrating a )#spool, high#bypass turbofan engine
with an unmixed exhaust. Again, the fan and booster stages are driven
by the low#pressure turbine, but more stages are re'uired. A mixed
exhaust is often employed nowadays
The low specific thrust>high bypass ratio turbofans used in todays civil
jetliners and some military transport aircraft evolved from the high
specific thrust>low bypass ratio turbofans used in such aircraft bac" in the
7%6s.
1ow specific thrust is achieved by replacing the multi#stage fan with a
single stage unit. Enli"e some military engines, modern civil turbofans
do not have any 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 sufficient =ore
Power to at least drive the fan at its design flow and pressure ratio.
Through improvements in turbine cooling>material technology, a higher
HP turbine rotor inlet temperature can be used, thus facilitating a
smaller and lighter core and potentially improving the core thermal
efficiency. ?educing the core mass flow tends to increase the load on the
1P turbine, so this unit may re'uire additional stages to reduce theaverage stage loading and to maintain 1P turbine efficiency. ?educing
core flow also increases bypass ratio G, or more, is now common.
9urther improvements in core thermal efficiency can be achieved by
raising the overall pressure ratio of the core. +mproved blade
aerodynamics reduces the number of extra compressor stages re'uired.
;ith multiple compressors i.e. 1P=, +P=, HP= dramatic increases in
overall pressure ratio have become possible. Dariable geometry
i.e. stators enable high pressure ratio compressors to wor" surge#free atall throttle settings.
@
http://en.wikipedia.org/wiki/Axial_compressor#Bleed_air.2C_variable_statorshttp://en.wikipedia.org/wiki/File:Turbofan_operation.svghttp://en.wikipedia.org/wiki/Axial_compressor#Bleed_air.2C_variable_stators -
5/20/2018 turbofan engine
9/47
Turbofan
=utaway diagram of the 3eneral 2lectric =9%#% engine
The first high#bypass turbofan engine was the 3eneral 2lectric T9&7,
designed in mid 7%6s to power the 1oc"heed=# 3alaxymilitary
transport aircraft. The civil 3eneral 2lectric =9%engine used a derived
design. *ther high#bypass turbofans are the Pratt : ;hitney 32nxand
the 3P5666, produced jointly by 32 and P:;.
High#bypass turbofan engines are generally 'uieter than the earlier low
bypass ratio civil engines. This is not so much due to the higher bypass
ratio, as to the use of a low pressure ratio, single stage, fan, which
significantly reduces specific thrust and, thereby, jet velocity. The
combination of a higher overall pressure ratio and turbine inlettemperature improves thermal efficiency. This, together with a lower
specific thrust better propulsive efficiency, leads to a lower specific fuel
consumption.
9or reasons of fuel economy, and also of reduced noise, almost all of
todays jet airliners are powered by high#bypass turbofans. Although
modern combat aircraft tend to use low bypass ratio turbofans, military
transport aircraft e.g. =#5 mainly use high bypass ratio turbofans
or turboprops for fuel efficiency.
0ecause of the implied low mean jet velocity, a high bypass ratio>low
specific thrust turbofan has a high thrust lapse rate with rising flight
speed. =onse'uently the engine must be over#si/ed to give sufficient
thrust during climb>cruise at high flight speeds e.g. $ach 6.@&. 0ecause
of the high thrust lapse rate, the static i.e. $ach 6 thrust is conse'uently
relatively high. This enables heavily laden, wide body aircraft to
accelerate 'uic"ly during ta"e#off and conse'uently lift#off within a
reasonable runway length.
7
http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/Lockheed_Corporationhttp://en.wikipedia.org/wiki/C-5_Galaxyhttp://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/Pratt_%26_Whitney_JT9Dhttp://en.wikipedia.org/wiki/Rolls-Royce_RB211http://en.wikipedia.org/wiki/CFM_International_CFM56http://en.wikipedia.org/wiki/Pratt_%26_Whitney_PW4000http://en.wikipedia.org/wiki/Rolls-Royce_Trenthttp://en.wikipedia.org/wiki/General_Electric_GE90http://en.wikipedia.org/wiki/GEnxhttp://en.wikipedia.org/wiki/GP7000http://en.wikipedia.org/wiki/C-17_Globemaster_IIIhttp://en.wikipedia.org/wiki/Turbopropshttp://en.wikipedia.org/wiki/File:CF6-6_engine_cutaway.jpghttp://en.wikipedia.org/wiki/File:CF6-6_engine_cutaway.jpghttp://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/Lockheed_Corporationhttp://en.wikipedia.org/wiki/C-5_Galaxyhttp://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/Pratt_%26_Whitney_JT9Dhttp://en.wikipedia.org/wiki/Rolls-Royce_RB211http://en.wikipedia.org/wiki/CFM_International_CFM56http://en.wikipedia.org/wiki/Pratt_%26_Whitney_PW4000http://en.wikipedia.org/wiki/Rolls-Royce_Trenthttp://en.wikipedia.org/wiki/General_Electric_GE90http://en.wikipedia.org/wiki/GEnxhttp://en.wikipedia.org/wiki/GP7000http://en.wikipedia.org/wiki/C-17_Globemaster_IIIhttp://en.wikipedia.org/wiki/Turboprops -
5/20/2018 turbofan engine
10/47
Turbofan
The turbofans on twin engined airliners are further over#si/ed to cope
with losing one engine during ta"e#off, which reduces the aircrafts net
thrust by 6C. $odern twin engined airliners normally climb very
steeply immediately after ta"e#off. +f one engine is lost, the climb#out is
much shallower, but sufficient to clear obstacles in the flightpath.
The (oviet Enions engine technology was less advanced than the ;ests
and its first wide#body aircraft, the +lyushin +l#@%, was powered by low#
bypass engines. The Ia"ovlev Ia"#8), a medium#range, rear#engined
aircraft seating up to )6 passengers introduced in 7@6 was the first
(oviet aircraft to use high#bypass engines.
Turbofan configurations
Turbofan engines come in a variety of engine configurations. 9or a given
engine cycle i.e. same airflow, bypass ratio, fan pressure ratio, overall
pressure ratio and HP turbine rotor inlet temperature, the choice of
turbofan configuration has little impact upon the design point
performance e.g. net thrust, (9=, as long as overall component
performance is maintained. *ff#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 throttle the compression system, without
encountering an instability "nown as compressor surge. This occurs when
some of the compressor aerofoils stall li"e the wings of an aircraft
causing a violent change in the direction of the airflow. However,
compressor stall can be avoided, at throttled conditions, by progressivelyG
opening interstage>intercompressor blow#off valves inefficient
and>or
) closing variable stators within the compressor
$ost modern American civil turbofans employ a relatively high pressure
ratio High Pressure HP =ompressor, with many rows of variable stators
to control surge margin at part#throttle. +n the three#
spool ?0)>Trentthe core compression system is split into two, with the
+P compressor, which supercharges the HP compressor, being on a
different coaxial shaft and driven by a separate +P turbine. As the HP
=ompressor has a modest pressure ratio it can be throttled#bac" surge#
free, without employing variable geometry. However, because a shallow
6
http://en.wikipedia.org/wiki/Ilyushin_Il-86http://en.wikipedia.org/wiki/Yakovlev_Yak-42http://en.wikipedia.org/wiki/RB211http://en.wikipedia.org/wiki/Trenthttp://en.wikipedia.org/wiki/Ilyushin_Il-86http://en.wikipedia.org/wiki/Yakovlev_Yak-42http://en.wikipedia.org/wiki/RB211http://en.wikipedia.org/wiki/Trent -
5/20/2018 turbofan engine
11/47
Turbofan
+P compressor wor"ing line is inevitable, the +P= re'uires at least one
stage of variable geometry.
[edit]Single shaft turbofan
Although far from common, the (ingle (haft Turbofan is probably thesimplest configuration, comprising a fan and high pressure compressor
driven by a single turbine unit, all on the same shaft. The (B2=$A $&,
which powers $irage fighter aircraft, is an example of a (ingle (haft
Turbofan. 4espite the simplicity of the turbomachinery configuration, the
$& re'uires a variable area mixer to facilitate part#throttle operation.
Aft fan turbofan
*ne of the earliest turbofans was a derivative of the 3eneral 2lectric
-
5/20/2018 turbofan engine
12/47
Turbofan
$ost modern passenger and military aircraft are powered by gas
turbineengines, which are also called jet engines. There are several
different typesof gas turbine engines, but all turbine engines have
somepartsin common. All turbine engines have an inletto bring free
streamair into the engine. The inlet sits upstream of the compressorand,
while the inlet does no wor" on the flow, inlet performancehas a strong
influence on engine net thrust. As shown in the figures above, inlets come
in a variety of shapes and si/es with the specifics usually dictated by thespeed of the aircraft.
S!S"#$% $#&ETS
9or aircraft that cannot go faster than the speed of sound, li"e large
airliners, a simple, straight, short inlet wor"s 'uite well. *n a
typical subsonicinlet, the surface of the inlet from outside to inside is a
continuous smooth curve with some thic"ness from inside to outside. The
most upstream portion of the inlet is called the highlight, or the
inlet lip'A subsonic aircraft has an inlet with a relatively thic" lip.
)
http://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/atmos.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/atmos.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inleth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thsum.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/sound.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/hisub.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/atmos.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/atmos.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inleth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thsum.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/sound.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/hisub.html -
5/20/2018 turbofan engine
13/47
Turbofan
S(E)S"#$% $#&ETS
An inlet for a supersonicaircraft, on the other hand, has a relatively sharp
lip. The inlet lip is sharpened to minimi/e the performance losses
from shoc" wavesthat occur during supersonic flight. 9or a supersonicaircraft, the inlet must slow the flow down to subsonic speeds before the
air reaches the compressor. (ome supersonic inlets, li"e the one at the
upper right, use a central cone to shoc" the flow down to subsonic speeds.
*ther inlets, li"e the one shown at the lower left, use flat hinged plates to
generate the compression shoc"s, with the resulting inlet geometry
having a rectangular cross section. This *ariable geometryinlet is used
on the 9#8 and 9# fighter aircraft. $ore exotic inlet shapes are used on
some aircraft for a variety of reasons. The inlets of the $ach &J(?#5
aircraft are specially designed to allow cruisingflight at high speed. The
inlets of the (?#5 actually produce thrust during flight.
H+(E)S"#$% $#&ETS
+nlets for hypersonicaircraft present the ultimate design challenge.
9or ramjet#poweredaircraft, the inlet must bring the high speed external
flow down to subsonic conditions in theburner. High stagnation
temperatures are present in this speed regime and variable geometry may
not be an option for the inlet designer because of possible flow lea"s
through the hinges. 9or scramjet#poweredaircraft, the heat environmentis even worse because the flight $ach number is higher than that for a
ramjet#powered aircraft. (cramjet inlets are highly integrated with the
fuselage of the aircraft. *n the K#8&A, the inlet includes the entire lower
surface of the aircraft forward of the cowl lip. Thic", hotboundary
layersare usually present on the compression surfaces of hypersonic
inlets. The flow exiting a scramjet inlet must remain supersonic.
$#&ET E,,$%$E#%+
An inlet must operate efficiently over the entire flight envelope of the
aircraft. At very low aircraft speeds, or when just sitting on the runway,
free stream air is pulled into the engine by the compressor. +n 2ngland,
inlets are called intakeswhich is a more accurate description of their
function at low aircraft speeds. At high speeds, a good inlet will allow the
aircraft to maneuver to high angles of attac"and sideslip without
disrupting flow to the compressor. 0ecause the inlet is so important to
overall aircraft operation, it is usually designed and tested by the airframe
company, not the engine manufacturer. 0ut because inlet operation is so
important to engine performance, all engine manufacturers also employ
&
http://www.grc.nasa.gov/WWW/K-12/airplane/lowsup.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/shock.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/hisup.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/cruise.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/lowhyper.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burner.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/scramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/incline.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/lowsup.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/shock.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/hisup.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/cruise.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/lowhyper.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burner.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/scramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/incline.html -
5/20/2018 turbofan engine
14/47
Turbofan
inlet aerodynamicists. The amount of disruption of the flow is
characteri/ed by a numerical inlet distortion inde.. 4ifferent airframers
use different indices, but all of the indices are based on ratios of the local
variation of pressure to the average pressure at the compressor face.
The ratio of the average total pressure at the compressor face to the free
stream total pressure is called the total pressure reco*ery.
Pressure recoveryis another inlet performance indexL the higher the
value, the better the inlet. 9or hypersonic inlets the value of pressure
recovery is very low and nearly constant because of shoc" losses, so
hypersonic inlets are normally characteri/ed by their "inetic energy
efficiency. +f the airflow demanded by the engine is much less than the
airflow that can be captured by the inlet, then the difference in airflow is
spilled around the inlet. The airflow mis#match can producespillage
drag on the aircraft.
$ost modern passenger and military aircraft are powered by gas
turbineengines, which are also called jet engines. There are several
different typesof jet engines, but all jet engines have somepartsin
8
http://www.grc.nasa.gov/WWW/K-12/airplane/inleth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/normal.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inleth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/normal.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.html -
5/20/2018 turbofan engine
15/47
Turbofan
common. All jet engines have a compressorto increase the pressure of the
incoming air before it enters the burner. =ompressor performancehas a
large influence on total engineperformance.
There are two main types of compressors used in modern jet enginesL
axial compressors , and centrifugal compressors.
+n the a.ial compressorthe air flows parallel to the axis of rotation. The
compressor is composed of several rows of airfoil cascades. (ome of the
rows, called rotors, are connectedto the central shaft and rotate at high
speed. *ther rows, called stators, are fixed and do not rotate. The job of
the stators is to increase pressure and "eep the flow from spiraling around
the axis by bringing the flow bac" parallel to the axis. +n the figure on the
right, we see a picture of the rotors of an axial compressor. The stators ofthis compressor are connected to the outer casing, which has been
removed and is not shown. At the upper left is a picture of a single rotor
stage for a different compressor so that you can see how the individual
blades are shaped and aligned. At the bottom of the figure is a computer
generated figure of an entire axial compressor with both rotors and
stators. The compressor is attached to a shaft which is connected to
thepower turbineon the right end of the blue shaft. Here is an animated
version of the axial compressorG
http://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thsum.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/centrf.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ctmatch.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thsum.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/centrf.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ctmatch.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.html -
5/20/2018 turbofan engine
16/47
Turbofan
How does an a.ial compressor work?
The details are 'uite complex because the blade geometries and theresulting flows are three dimensional, unsteady, and can have
important viscous and compressibilityeffects. 2ach blade on a rotor or
stator produces a pressure variation much li"e the airfoilof a
spinningpropeller.0ut unli"e a propeller blade, the blades of an axial
compressor are close to one another, which seriously alters the flow
around each blade. =ompressor blades continuously pass through the
wa"es of upstream blades that introduce unsteady flow variations.
=ompressor designers must rely on wind tunneltesting and
sophisticated computational modelsto determine the performance of an
axial compressor. The performance is characteri/ed by the pressure ratio
across the compressor %(), the rotational speed of the shaft necessary to
produce the pressure increase, and an efficiency factor that indicates how
much additional wor" is re'uired relative to an ideal compressor. There
are additional important compressor topics, li"e stall and surge, that will
be added to these pages in the future.
%
http://www.grc.nasa.gov/WWW/K-12/airplane/airsim.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/right1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/tunnel1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/nseqs.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/airsim.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/right1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/tunnel1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/nseqs.html -
5/20/2018 turbofan engine
17/47
Turbofan
$ost modern passenger and military aircraft are powered by gasturbineengines, which are also called jet engines. There are several
different typesof gas turbine engines, and all turbine engines have
somepartsin common. All turbine engines have a combustor,
or burner, in which the fuel is combined with high pressure air
andburned.The resulting high temperature exhaust gas is used to turn
thepower turbineand produce thrustwhen passed through a no//le.
0urners are also used on ramjetand scramjetpropulsion systems. The
design of ramjet and scramjet burners are slightly different than the
burners used on gas turbine engines, although the basic thermodynamicprinciplesare the same.
*n this page, we discuss the operation of a gas turbine burner. The burner
is shown in red on the computer graphic at the lower right of the figure.
The burner sits between the compressorand the power turbine. The
burner is arranged li"e anannulus, or a doughnut, as shown by the three
burner configurations at the lower left. The central shaft that connects the
turbine and compressor passes through the center hole. 0urners are made
from materials that can withstand the hightemperaturesof combustion. Aburner usually has an outer casing, shown in red, and an inner liner,
shown in orange. The liner is often perforated to enhance mixing of the
fuel and air, as shown in the photo at the upper right.
There are three main types of combustors, and all three designs are found
in modern gas turbinesG
. The burner at the left is an annularcombustor with the liner sitting
inside the outer casing which has been peeled open in the drawing.
$any modern burners have an annular design.
). The burner in the middle is an older canor tubular design. The
photo at the top left shows some actual burner cans. 2ach can has
both a liner and a casing, and the cans are arranged around the
central shaft.&. A compromise design is shown at the right. This is a can-
annulardesign, in which the casing is annular and the liner is can#
shaped. The advantage to the can#annular design is that the
individual cans are more easily designed, tested, and serviced.
5
http://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/combst1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrsteq.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/scramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thermo.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thermo.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/temptr.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/combst1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrsteq.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/scramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thermo.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thermo.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/temptr.html -
5/20/2018 turbofan engine
18/47
Turbofan
The details of mixing and burning the fuel are 'uite complex and re'uire
extensive testing for a new burner. 9or our purposes, we can consider
the burneras simply the place where combustion occurs and where the
wor"ing fluid air temperature is raised with a slight decreasein
pressure.
$ost modern passenger and military aircraft are powered by gas
turbineengines, which are also called jet engines. There are several
different typesof gas turbine engines, but all turbine engines have
somepartsin common. All gas turbine engines have a powerturbinelocated downstream of theburnerto extract energy from the hot
flow and turn thecompressor. ;or"is done on the power turbine by the
hot exhaust flow from the burner.
/escription of $mages
The bottom of the figure showsG
computer drawings of a turbojetwith the location of the turbine
relative to the other engine components, on the right
@
http://www.grc.nasa.gov/WWW/K-12/airplane/burnth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burner.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powtrbth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbj.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burnth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/burner.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powtrbth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbj.html -
5/20/2018 turbofan engine
19/47
Turbofan
the turbine section alone with the central shaft attached to the
turbine, on the left.
+n both drawings, the turbine is magenta in color and the shaft is colored
blue. The left end of the shaft would be attached to the compressor,whichis colored cyan in the drawing on the right. Here is an animated version
of the turbine sectionG
The upper left of the figure shows an actual power turbine. The turbine,li"e the compressor, is composed of several rows of airfoil cascades.
(ome of the rows, called rotors, are connectedto the central shaft and
rotate at high speed. *ther rows, called stators, are fixed and do not
rotate. The job of the stators is to "eep the flow from spiraling around the
axis by bringing the flow bac" parallel to the axis.
4epending on the engine type,there may be multiple turbine stages
present in the engine. Turbofanand turbopropengines usually employ a
separate turbine and shaft to power the fan and gear box respectively.(uch an arrangement is termed atwo spoolengine. 9or some high
performance engines, an additional turbine and shaft is present to power
separate parts of the compressor. This arrangement produces a three
spoolengine. The power turbine shown on the upper left of the figure is
for a two spool, turbofan engine.
/esign /etails
7
http://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ctmatch.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/compress.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ctmatch.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbp.html -
5/20/2018 turbofan engine
20/47
Turbofan
There are several interesting turbine design details present on this slide.
(ince the turbine extracts energy from the flow, the
pressure decreasesacross the turbine. The pressure gradient helps "eep
theboundary layerflow attached to the surface of the turbine blades.
(ince the boundary layer is less li"ely to separate on a turbine blade thanon a compressor blade, the pressure drop across a single turbine stage can
be much greater than the pressure increase across a corresponding
compressor stage. A single turbine stage can be used to dri*e multiple
compressor stages'0ecause of the high pressure change across the
turbine, the flow tends to lea" around the tips of the blades. The tips of
turbine blades are often connected by a thin metal band to "eep the flow
from lea"ing, as shown in the picture at the upper left.
Turbine blades exist in a much more hostile environment than compressor
blades. (itting just downstream of the burner, the blades experience flow
temperatures of more than a thousand degrees 9ahrenheit. Turbine blades
must be made of special materials that can withstand the heat, or they
must be actively cooled. At the upper right of the figure, we show a
picture of a single, actively cooled turbine blade. The blade is hollow and
cool air, which is bled off the compressor, is pumped through the blade
and out through the small holes on the surface to "eep the surface cool.
)6
http://www.grc.nasa.gov/WWW/K-12/airplane/powtrbth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powtrbth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.html -
5/20/2018 turbofan engine
21/47
Turbofan
$ost modern passenger and military aircraft are powered by gas
turbineengines, which are also called jet engines. There are several
different typesof gas turbine engines, but all turbine engines have
somepartsin common. All gas turbine engines have a no00leto
produce thrust,to conduct the exhaust gases bac" to the free stream,and
to set the mass flow ratethrough the engine. The no//le sits downstream
of thepower turbine.
A no//le is a relatively simple device, just a specially shaped tube
through which hot gases flow. However, the mathematicswhich describe
the operation of the no//le ta"es some careful thought. As shown above,
no//les come in a variety of shapes and si/es depending on the mission of
the aircraft. (imple turbojets,and turboprops,often have a fixed
geometrycon*ergentno//le as shown on the left of the
figure. Turbofanengines often employ a co-annularno//le as shown at
the top left. The core flow exits the center no//le while the fan flow exits
the annular no//le. $ixing of the two flows provides some thrustenhancement and these no//les also tend to be 'uieter than convergent
)
http://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/atmos.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/nozzleh.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbj.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/trbtyp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/atmos.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/powturb.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/nozzleh.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbj.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbp.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.html -
5/20/2018 turbofan engine
22/47
Turbofan
no//les. Afterburning turbojetsand turbofans re'uire a variable
geometry con*ergent-di*ergent - %/no//le as shown on the left. +n this
no//le, the flow first converges down to the minimum
areaor throatthen is expanded through the divergent section to the exit
at the right. The variable geometry causes these no//les to be heavierthan a fixed geometry no//le, but variable geometry provides efficient
engine operation over a wider airflow range than a simple fixed no//le.
?oc"et enginesalso use no//les to accelerate hot exhaust to produce
thrust. ?oc"et engines usually have a fixed geometry =4 no//le with a
much larger divergent section than is re'uired for a gas turbine. Iou can
explore the design and operation of no//les with our interactive no//le
simulatorprogram which runs on your browser.
All of the no//les we have discussed thus far are round tubes. ?ecently,
however, engineers have been experimenting with no//les with
rectangular exits. This allows the exhaust flow to be easily deflected,
or vectored, as shown in the middle of the figure. =hanging the direction
of the thrust with the no//le ma"es the aircraft much more maneuverable.
0ecause the no//le conducts the hot exhaust bac" to the free stream, there
can be serious interactions between the engine exhaust flow and the
airflow around the aircraft. *n fighter aircraft, in particular, large drag
penalties can occur near the no//le exits. A typical no00le-afterbodyconfiguration is shown in the upper right for an 9# with
experimental maneuvering no//les. As with the inletdesign, the external
no//le configuration is often designed by the airframer. The internal
no//le is usually the responsibility of the engine manufacturer.
Contents
[hide]
1 Introduction
2 Early turbofans
3 Low bypass turbofans
4 Afterburning turbofans
5 igh!bypass turbofan engines
" #urbofan configurations
o "$1 %ingle shaft turbofan
o "$2 Aft fan turbofan
))
http://www.grc.nasa.gov/WWW/K-12/airplane/aturba.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rockth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ienzl.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ienzl.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/vecthrst.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inlet.htmlhttp://toggletoc%28%29/http://en.wikipedia.org/wiki/Turbofan#Introductionhttp://en.wikipedia.org/wiki/Turbofan#Early_turbofanshttp://en.wikipedia.org/wiki/Turbofan#Low_bypass_turbofanshttp://en.wikipedia.org/wiki/Turbofan#Afterburning_turbofanshttp://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan_engineshttp://en.wikipedia.org/wiki/Turbofan#Turbofan_configurationshttp://en.wikipedia.org/wiki/Turbofan#Single_shaft_turbofanhttp://en.wikipedia.org/wiki/Turbofan#Aft_fan_turbofanhttp://www.grc.nasa.gov/WWW/K-12/airplane/aturba.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/mflchk.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rockth.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ienzl.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ienzl.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/vecthrst.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/inlet.htmlhttp://toggletoc%28%29/http://en.wikipedia.org/wiki/Turbofan#Introductionhttp://en.wikipedia.org/wiki/Turbofan#Early_turbofanshttp://en.wikipedia.org/wiki/Turbofan#Low_bypass_turbofanshttp://en.wikipedia.org/wiki/Turbofan#Afterburning_turbofanshttp://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan_engineshttp://en.wikipedia.org/wiki/Turbofan#Turbofan_configurationshttp://en.wikipedia.org/wiki/Turbofan#Single_shaft_turbofanhttp://en.wikipedia.org/wiki/Turbofan#Aft_fan_turbofan -
5/20/2018 turbofan engine
23/47
Turbofan
o "$3 &asic two spool
o "$4 &oosted two spool
o "$5 #hree spool
o "$" 'eared fan
o "$( )ilitary turbofans
o "$* igh +ressure #urbine
o "$, Low +ressure #urbine
( -ycle i.pro/e.ents
* #hrust growth
, #echnical 0iscussion
1 ecent de/elop.ents in blade technology
11 #urbofan engine .anufacturers
o 11$1 'eneral Electric
o 11$2 -) International
o 11$3 olls!oyce
o 11$4 +ratt hitney
o 11$5 A/iad/igatel
12 E6tre.e bypass 7et engines
13 #er.inology
14 8ther .eanings
15 9otes and references
Welcome to the Beginner's Guide toPropulsion
)&
http://en.wikipedia.org/wiki/Turbofan#Basic_two_spoolhttp://en.wikipedia.org/wiki/Turbofan#Basic_two_spoolhttp://en.wikipedia.org/wiki/Turbofan#Boosted_two_spoolhttp://en.wikipedia.org/wiki/Turbofan#Boosted_two_spoolhttp://en.wikipedia.org/wiki/Turbofan#Three_spoolhttp://en.wikipedia.org/wiki/Turbofan#Three_spoolhttp://en.wikipedia.org/wiki/Turbofan#Geared_fanhttp://en.wikipedia.org/wiki/Turbofan#Military_turbofanshttp://en.wikipedia.org/wiki/Turbofan#High_Pressure_Turbinehttp://en.wikipedia.org/wiki/Turbofan#Low_Pressure_Turbinehttp://en.wikipedia.org/wiki/Turbofan#Cycle_improvementshttp://en.wikipedia.org/wiki/Turbofan#Thrust_growthhttp://en.wikipedia.org/wiki/Turbofan#Technical_Discussionhttp://en.wikipedia.org/wiki/Turbofan#Recent_developments_in_blade_technologyhttp://en.wikipedia.org/wiki/Turbofan#Turbofan_engine_manufacturershttp://en.wikipedia.org/wiki/Turbofan#General_Electrichttp://en.wikipedia.org/wiki/Turbofan#CFM_Internationalhttp://en.wikipedia.org/wiki/Turbofan#CFM_Internationalhttp://en.wikipedia.org/wiki/Turbofan#Rolls-Roycehttp://en.wikipedia.org/wiki/Turbofan#Pratt_.26_Whitneyhttp://en.wikipedia.org/wiki/Turbofan#Aviadvigatelhttp://en.wikipedia.org/wiki/Turbofan#Aviadvigatelhttp://en.wikipedia.org/wiki/Turbofan#Extreme_bypass_jet_engineshttp://en.wikipedia.org/wiki/Turbofan#Terminologyhttp://en.wikipedia.org/wiki/Turbofan#Other_meaningshttp://en.wikipedia.org/wiki/Turbofan#Notes_and_referenceshttp://en.wikipedia.org/wiki/Turbofan#Basic_two_spoolhttp://en.wikipedia.org/wiki/Turbofan#Boosted_two_spoolhttp://en.wikipedia.org/wiki/Turbofan#Three_spoolhttp://en.wikipedia.org/wiki/Turbofan#Geared_fanhttp://en.wikipedia.org/wiki/Turbofan#Military_turbofanshttp://en.wikipedia.org/wiki/Turbofan#High_Pressure_Turbinehttp://en.wikipedia.org/wiki/Turbofan#Low_Pressure_Turbinehttp://en.wikipedia.org/wiki/Turbofan#Cycle_improvementshttp://en.wikipedia.org/wiki/Turbofan#Thrust_growthhttp://en.wikipedia.org/wiki/Turbofan#Technical_Discussionhttp://en.wikipedia.org/wiki/Turbofan#Recent_developments_in_blade_technologyhttp://en.wikipedia.org/wiki/Turbofan#Turbofan_engine_manufacturershttp://en.wikipedia.org/wiki/Turbofan#General_Electrichttp://en.wikipedia.org/wiki/Turbofan#CFM_Internationalhttp://en.wikipedia.org/wiki/Turbofan#Rolls-Roycehttp://en.wikipedia.org/wiki/Turbofan#Pratt_.26_Whitneyhttp://en.wikipedia.org/wiki/Turbofan#Aviadvigatelhttp://en.wikipedia.org/wiki/Turbofan#Extreme_bypass_jet_engineshttp://en.wikipedia.org/wiki/Turbofan#Terminologyhttp://en.wikipedia.org/wiki/Turbofan#Other_meaningshttp://en.wikipedia.org/wiki/Turbofan#Notes_and_references -
5/20/2018 turbofan engine
24/47
Turbofan
What is propulsion? The word isderived from two Latinwords:promeaning before orforwards andpelleremeaning todrive. Propulsionmeans to pushforward or drive an object
forward. A propulsion system is amachine that producesthrusttopush an object forward. Onairplanes thrust is usuallygenerated through someapplication of !ewton"sthirdlaw of action and reaction. A gasor working fluid is acceleratedby the engine and the reaction tothis acceleration produces aforce on the engine.
)8
http://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton3.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton3.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton3.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/thrust1.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton3.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton3.html -
5/20/2018 turbofan engine
25/47
Turbofan
A general derivation of the thrust e#uationshows that the amount of thrust generateddepends on the mass flow through the engine and the e$it velocity of the gas. %ifferentpropulsion systems generate thrust in slightly different ways. We will discuss four principalpropulsion systems: the propellertheturbine &or jet'engine the ramjetand theroc(et.
Why are there different types of engines? )f we thin( about !ewton"sfirst lawof motion we
reali*e that an airplane propulsion system must serve two purposes. +irst the thrust fromthe propulsion system mustbalancethe drag of the airplane when the airplane is cruising.And second the thrust from the propulsion system must e$ceedthe drag of the airplanefor the airplane to accelerate. )n fact the greater the difference between the thrust and thedrag called thee$cess thrustthe faster the airplane will accelerate.
,ome aircraft li(e airliners and cargo planes spend most of their life in a cruise condition.+or these airplanes e$cess thrust is not as important as high engine efficiency andlow fuel usage.,ince thrust depends on both the amount of gas moved and the velocitywe can generate high thrust by accelerating a large mass of gas by a small amount or byaccelerating a small mass of gas by a large amount. -ecause of the aerodynamicefficiency ofpropellersand fansit is more fuel efficient to accelerate a large mass by asmall amount. That is why we find high bypass fans and turboprops on cargo planes andairliners.
,ome aircraft li(e fighter planes or e$perimental high speed aircraft re#uire very highe$cess thrust to accelerate #uic(ly and to overcome the high drag associated with highspeeds. +or these airplanes engine efficiency is not as important as very high thrust.odern military aircraft typically employ afterburnerson a low bypass turbofan core.+uture hypersonic aircraft will employ some type of ramjetor roc(et propulsion.
The site was prepared at !A,A /lenn by the Learning Technologies 0roject <0' toprovide background informationon basic propulsion for secondary math and scienceteachers. The pages were originally prepared as teaching aidsto support1ngine,im aninteractive educational computer program that allows students to design and test jet
engines on a personal computer. Other slides were prepared to support LT0videoconferencing wor(shops&http:22www.grc.nasa.gov2WWW2345627o127oemain.html' forteachers and students. And other slides were prepared as part of0ower 0oint0resentationsfor the %igital Learning !etwor(.
There is a special section of the -eginner"s /uide which deals with compressible or highspeed aerodynamics. This section is intended for undergraduateswho arestudying shoc( wavesor isentropic flowsand contains severalcalculators andsimulatorsfor that flow regime.
Common types
#here are two types of 7et engine that are seen
co..only today: the turbofan which is used on al.ost
all co..ercial airliners: and roc;et engineswhich are
used for spaceflightand other terrestrial uses such as
e7ector seats: flares: firewor;s etc$
)
http://www.grc.nasa.gov/WWW/K-12/airplane/thrsteq.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propeller.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton1a.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton1a.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton1a.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/cruise.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/cruise.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/smotion.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/smotion.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/exthrst.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/exthrst.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/sfc.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propeller.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propeller.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propeller.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbfan.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbfan.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbab.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.htmlhttp://www.grc.nasa.gov/WWW/K-12/CoE/Coemain.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/topics.htmhttp://www.grc.nasa.gov/WWW/K-12/airplane/topics.htmhttp://www.grc.nasa.gov/WWW/K-12/airplane/topics.htmhttp://www.grc.nasa.gov/WWW/K-12/airplane/topics.htmhttp://nasadln.nmsu.edu/dln/http://www.grc.nasa.gov/WWW/K-12/airplane/shortc.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/oblique.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/oblique.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/isentrop.htmlhttp://www.grc.nasa.gov/WWW/K-12/UndergradProgs/index.htmhttp://www.grc.nasa.gov/WWW/K-12/UndergradProgs/index.htmhttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Spaceflighthttp://www.grc.nasa.gov/WWW/K-12/airplane/thrsteq.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propeller.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/newton1a.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/cruise.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/smotion.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/exthrst.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/sfc.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/propeller.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbfan.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/turbab.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/rocket.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.htmlhttp://www.grc.nasa.gov/WWW/K-12/CoE/Coemain.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/topics.htmhttp://www.grc.nasa.gov/WWW/K-12/airplane/topics.htmhttp://nasadln.nmsu.edu/dln/http://www.grc.nasa.gov/WWW/K-12/airplane/shortc.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/oblique.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/isentrop.htmlhttp://www.grc.nasa.gov/WWW/K-12/UndergradProgs/index.htmhttp://www.grc.nasa.gov/WWW/K-12/UndergradProgs/index.htmhttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Spaceflight -
5/20/2018 turbofan engine
26/47
Turbofan
[edit]Turbofan enginesMain article: Turbofan
)ost .odern 7et engines are actually turbofans: where
the low pressure co.pressor acts as a fan: supplyingsupercharged air not only to the engine core: but to a
bypass duct$ #he bypass airflow either passes to a
separate
-
5/20/2018 turbofan engine
27/47
Turbofan
[edit]Rocket enginesMain article: Rocket engine
A co..on for. of 7et engine is the roc;et engine$
oc;et engines are used for high altitude flights becausethey gi/e /ery high thrustand their lac; of reliance on
at.ospheric o6ygen allows the. to operate at arbitrary
altitudes$
#his is used for launching satellites: space
e6plorationand .anned access: and per.itted landing
on the .oonin 1,",$
owe/er: the high e6haust speed and the hea/ier:o6idiser!rich propellant results in .ore propellant use
than turbo7ets: and their use is largely restricted to /ery
high altitudes: /ery high speeds: or where /ery high
accelerations are needed as roc;et engines the.sel/es
ha/e a /ery high thrust!to!weight ratio$
An appro6i.ate e@uation for the net thrust of a roc;et
engine is
hereFis the thrust:'sp(acis the specific
i.pulse:g6is a standard gra/ity: is the propellant
flow in ;gBs:Aeis the area of the e6haust bell at the
e6it: and)is the at.ospheric pressure$
[edit]General physical principles
All 7et engines are reaction engines that generate
thrust by e.itting a7etof fluid rearwards at relati/ely
high speed$ #he forces on the inside of the engine
needed to create this 7et gi/e a strong thrust on the
engine which pushes the craft forwards$
Cet engines .a;e their 7et fro. propellant fro.
tan;age that is attached to the engine >as in a
-
5/20/2018 turbofan engine
28/47
Turbofan
fluid >/ery typically air? and e6pelling it at higher
speed$
[edit]Thrust
#he .otion i.pulse of the engine is e@ual to the fluid.ass .ultiplied by the speed at which the engine
e.its this .ass
I D . c
where . is the fluid .ass per second and c is the
e6haust speed$ In other words: a /ehicle gets the
sa.e thrust if it outputs a lot of e6haust /ery
slowly: or a little e6haust /ery @uic;ly$ >In practice
parts of the e6haust .ay be faster than others:
but it
-
5/20/2018 turbofan engine
29/47
Turbofan
% D . >c!/?
#his e@uation i.plies that as / approaches
c: a greater .ass of fluid .ust go through
the engine to continue to accelerate at thesa.e rate: but all engines ha/e a designed
li.it on this$ Additionally: the e@uation
i.plies that the /ehicle canF? upon the
/ehicle speedBe6haust speed ratio >/Bc? for air!
breathing 7et and roc;et engines
Energy efficiency >M? of 7et engines installedin /ehicles has two .ain
co.ponents: cycle efficiency>Mc?! how
efficiently the engine can accelerate the
7et: andpropulsive efficiency>Mp?!how .uch
of the energy of the 7et ends up in the
/ehicle body rather than being carried
away as ;inetic energy of the 7et$
E/en though o/erall energy efficiency Missi.ply
M N MpMc
or all 7et engines thepropulsive
efficiencyis highest when the engine
e.its an e6haust 7et at a speed that is
the sa.e as: or nearly the sa.e as: the
/ehicle /elocity as this gi/es the
s.allest residual ;inetic
)7
http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=10http://en.wikipedia.org/wiki/Propulsive_efficiencyhttp://en.wikipedia.org/wiki/Propulsive_efficiencyhttp://en.wikipedia.org/wiki/File:Propulsive_efficiency.pnghttp://en.wikipedia.org/wiki/File:Propulsive_efficiency.pnghttp://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=10http://en.wikipedia.org/wiki/Propulsive_efficiencyhttp://en.wikipedia.org/wiki/Propulsive_efficiency -
5/20/2018 turbofan engine
30/47
Turbofan
energy$>9ote[2]? #he e6act for.ula for
air!breathing engines .o/ing at
speed (with an e6haust /elocity cis
gi/en in the literature as[21]is
And for a roc;et
[22]
In addition to propulsi/e
efficiency: another factor is cycle
efficiency essentially a 7et
engine is typically a for. of heat
engine$ eat engine efficiency is
deter.ined by the ratio of
te.peratures that are reached in
the engine to that they are
e6hausted at fro. the no==le:
which in turn is li.ited by
the o/erall pressure ratiothatcan be achie/ed$ -ycle efficiency
is highest in roc;et engines
>G"H?: as they can achie/e
e6tre.ely high co.bustion
te.peratures and can ha/e /ery
large: energy efficient no==les$
-ycle efficiency in turbo7et and
si.ilar is nearer to 3: thepractical co.bustion
te.peratures and no==le
efficiencies are .uch lower$
&6
http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-19http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-20http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-RPE-21http://en.wikipedia.org/wiki/Cycle_efficiencyhttp://en.wikipedia.org/wiki/Cycle_efficiencyhttp://en.wikipedia.org/wiki/Overall_pressure_ratiohttp://en.wikipedia.org/wiki/File:Specific-impulse-kk-20090105.pnghttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-19http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-20http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-RPE-21http://en.wikipedia.org/wiki/Cycle_efficiencyhttp://en.wikipedia.org/wiki/Cycle_efficiencyhttp://en.wikipedia.org/wiki/Overall_pressure_ratio -
5/20/2018 turbofan engine
31/47
Turbofan
%pecific i.pulseas a function of speed
for different 7et types with ;erosene
fuel >hydrogen Ispwould be about twice
as high?$ Although efficiency plu..etswith speed: greater distances are
co/ered: it turns out that efficiency per
unit distance >per ;. or .ile? is
roughly independent of speed for 7et
engines as a group howe/er airfra.es
beco.e inefficient at supersonic
speeds
[edit]Fuelpropellantconsumption
A closely related >but different?
concept to energy efficiency is
the rate of consu.ption of
propellant .ass$ +ropellant
consu.ption in 7et engines is
.easured by !pecific Fuel
Consumption: !pecificimpulseor Effective exhaust
velocity$ #hey all .easure the
sa.e thing: specific i.pulse and
effecti/e e6haust /elocity are
strictly proportional: whereas
specific fuel consu.ption is
in/ersely proportional to the
others$
or airbreathing engines such as
turbo7ets energy efficiency and
propellant >fuel? efficiency are
.uch the sa.e thing: since the
propellant is a fuel and the
source of energy$ In roc;etry: the
propellant is also the e6haust:
and this .eans that a highenergy propellant gi/es better
&
http://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=11http://en.wikipedia.org/wiki/Specific_Fuel_Consumptionhttp://en.wikipedia.org/wiki/Specific_Fuel_Consumptionhttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/File:Specific-impulse-kk-20090105.pnghttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=11http://en.wikipedia.org/wiki/Specific_Fuel_Consumptionhttp://en.wikipedia.org/wiki/Specific_Fuel_Consumptionhttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/Effective_exhaust_velocity -
5/20/2018 turbofan engine
32/47
Turbofan
propellant efficiency but can in
so.e cases actually can
gi/e lowerenergy efficiency$
Engine
type
scenari
o
S,%in
lb12lbf3
h4
S,%
in
g12k#3
s4
$spi
n s
Effecti*e
e.haust
*elocity2
m1s4
BF#&&roc
"et engine
vacuu
m6.7 &67 &&6 &,)86
(($2roc
"et engine
(pace(huttle
vacuu
m
5.7 )) 8& 8,8)&
?amjet $ 8. )5 @66 5,@55
(ne
cma
*lympus
7&
=oncor
de $)
cruise
dry
.7[)
&! &&.@ &,6) )7,&
=9%#
@6=)09
turbofan
0oeing585#
866
cruise
6.%6[)
&! 5. ,76 @,866
3eneral
2lectric
=9%turbo
fan
sea
level6.&65 @.%7%
,56
6,666
[23]
&)
http://en.wikipedia.org/wiki/Specific_fuel_consumption_(thrust)http://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/NK-33http://en.wikipedia.org/wiki/SSMEhttp://en.wikipedia.org/wiki/Ramjethttp://en.wikipedia.org/wiki/J-58http://en.wikipedia.org/wiki/J-58http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Specific_fuel_consumption_(thrust)http://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/Effective_exhaust_velocityhttp://en.wikipedia.org/wiki/NK-33http://en.wikipedia.org/wiki/SSMEhttp://en.wikipedia.org/wiki/Ramjethttp://en.wikipedia.org/wiki/J-58http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/General_Electric_CF6http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-LARGE-22 -
5/20/2018 turbofan engine
33/47
Turbofan
[edit]Thrust"to"#eightratioMain article: Thrust-to-weight
ratio#he thrust to weight ratio of 7et
engines of si.ilar principles
/aries so.ewhat with scale: but
.ostly is a function of engine
construction technology$ -learly
for a gi/en engine: the lighter the
engine: the better the thrust to
weight is: the less fuel is used toco.pensate for drag due to the
lift needed to carry the engine
weight: or to accelerate the .ass
of the engine$
As can be seen in the following
table: roc;et engines generally
achie/e /ery .uch higher thrust
to weight ratios than ductenginessuch as turbo7et and
turbofan engines$ #his is
pri.arily because roc;ets al.ost
uni/ersally use dense li@uid or
solid reaction .ass which gi/es a
.uch s.aller /olu.e and hence
the pressurisation syste. that
supplies the no==le is .uchs.aller and lighter for the sa.e
perfor.ance$ 0uct engines ha/e
to deal with air which is 2!3
orders of .agnitude less dense
and this gi/es pressures o/er
.uch larger areas: and which in
turn results in .ore engineering
.aterials being needed to hold
&&
http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=12http://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wiktionary.org/wiki/duct_enginehttp://en.wiktionary.org/wiki/duct_enginehttp://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=12http://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wiktionary.org/wiki/duct_enginehttp://en.wiktionary.org/wiki/duct_engine -
5/20/2018 turbofan engine
34/47
Turbofan
the engine together and for the
air co.pressor$
Engine
Thrust-to-
weight ratio
=oncordes ?olls#?oyce>(necma
*lympus 7&turbojet
8.6 with
reheat[)8!
left to
right? turboshaft: low
bypassandturbo7etto fly at 1 ;.
altitude in /arious speeds$ ori=ontal
a6is ! speed: .Bs$ Jertical a6is displays
engine efficiency$
#urbopropsobtain little thrust
fro. 7et effect: but are useful forco.parison$ #hey are gas turbine
&8
http://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wikipedia.org/wiki/Concordehttp://en.wikipedia.org/wiki/Concordehttp://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-23http://en.wikipedia.org/wiki/J-58http://en.wikipedia.org/wiki/J-58http://en.wikipedia.org/wiki/SR-71http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-24http://en.wikipedia.org/wiki/Space_shuttlehttp://en.wikipedia.org/wiki/Space_shuttlehttp://en.wikipedia.org/wiki/SSMEhttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-25http://en.wikipedia.org/wiki/RD-180http://en.wikipedia.org/wiki/RD-180http://en.wikipedia.org/wiki/NK-33http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-26http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=13http://en.wikipedia.org/wiki/Turboshafthttp://en.wikipedia.org/wiki/Turbofan#Low-bypass_turbofanshttp://en.wikipedia.org/wiki/Turbofan#Low-bypass_turbofanshttp://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Turboprophttp://en.wikipedia.org/wiki/File:JetSuitabilityEn.pnghttp://en.wikipedia.org/wiki/File:JetSuitabilityEn.pnghttp://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wikipedia.org/wiki/Thrust-to-weight_ratiohttp://en.wikipedia.org/wiki/Concordehttp://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-23http://en.wikipedia.org/wiki/J-58http://en.wikipedia.org/wiki/SR-71http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-24http://en.wikipedia.org/wiki/Space_shuttlehttp://en.wikipedia.org/wiki/SSMEhttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-25http://en.wikipedia.org/wiki/RD-180http://en.wikipedia.org/wiki/NK-33http://en.wikipedia.org/wiki/Jet_propulsion#cite_note-26http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=13http://en.wikipedia.org/wiki/Turboshafthttp://en.wikipedia.org/wiki/Turbofan#Low-bypass_turbofanshttp://en.wikipedia.org/wiki/Turbofan#Low-bypass_turbofanshttp://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/Turboprop -
5/20/2018 turbofan engine
35/47
Turbofan
engines that ha/e a rotating fan
that ta;es and accelerates the
large .ass of air but by a
relati/ely s.all change in speed$
#his low speed li.its the speed of
any propeller dri/en airplane$
hen the plane speed e6ceeds
this li.it: propellers no longer
pro/ide any thrust >c!/ K ?$
owe/er: because they
accelerate a large .ass of air:
turboprops are /ery efficient$
turbo7etsand other si.ilar
engines accelerate a .uch
s.aller .ass of the air and
burned fuel: but they e.it it at
the .uch higher speeds possible
with a de La/al no==le$ #his is
why they are suitable for
supersonic and higher speeds$
Low bypass turbofansha/e the
.i6ed e6haust of the two air
flows: running at different speeds
>c1 and c2?$ #he thrust of such
engine is
% D .1 >c1 ! /? H .2 >c2 ! /?
where .1 and .2 are the air
.asses: being blown fro. theboth e6hausts$ %uch engines
are effecti/e at lower speeds:
than the pure 7ets: but at
higher speeds than the
turboshafts and propellers in
general$ or instance: at the
1 ;. altitude: turboshafts
are .ost effecti/e atabout )ach$4 >$4 ti.es the
&
http://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/Turbofan#Low_bypass_turbofanshttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Turbojethttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/Turbofan#Low_bypass_turbofanshttp://en.wikipedia.org/wiki/Mach_number -
5/20/2018 turbofan engine
36/47
Turbofan
speed of sound?: low bypass
turbofans beco.e .ore
effecti/e at about )ach $(5
and turbo7ets beco.e .ore
effecti/e than .i6ed e6haust
engines when the speed
approaches )ach 2!3$
oc;et enginesha/e
e6tre.ely high e6haust
/elocity and thus are best
suited for high speeds
>hypersonic? and great
altitudes$ At any gi/en
throttle: the thrust and
efficiency of a roc;et .otor
i.pro/es slightly with
increasing altitude >because
the bac;!pressure falls thus
increasing net thrust at the
no==le e6it plane?: whereas
with a turbo7et >or turbofan?the falling density of the air
entering the inta;e >and the
hot gases lea/ing the no==le?
causes the net thrust to
decrease with increasing
altitude$ oc;et engines are
.ore efficient than e/en
scra.7ets abo/e roughly )ach15$[2*]
[edit]$ltitude andspeed
ith the e6ception
of scra.7ets: 7et engines:
depri/ed of their inlet syste.s
can only accept air at aroundhalf the speed of sound$ #he
&%
http://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Hypersonichttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-27http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=14http://en.wikipedia.org/wiki/Scramjethttp://en.wikipedia.org/wiki/Rocket_enginehttp://en.wikipedia.org/wiki/Hypersonichttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-27http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=14http://en.wikipedia.org/wiki/Scramjet -
5/20/2018 turbofan engine
37/47
Turbofan
inlet syste.
-
5/20/2018 turbofan engine
38/47
Turbofan
@uietest: whereas the fastest
7ets are the loudest$
Although so.e /ariation in 7et
speed can often be arrangedfro. a 7et engine >such as by
throttling bac; and ad7usting
the no==le? it is difficult to
/ary the 7et speed fro. an
engine o/er a /ery wide
range$ #herefore since
engines for supersonic
/ehicles such as -oncorde:
.ilitary 7ets and roc;ets
inherently need to ha/e
supersonic e6haust at top
speed: so these /ehicles are
especially noisy e/en at low
speeds$
[edit]$dvanced
designs[edit]&"'( combinedram)etturbo)et
#he %!(1 &lac;birdabo/e
)ach 2$4?: the engine used
/ariable geo.etry /anes to
direct e6cess air through "
bypass pipes fro.
downstrea. of the fourth
co.pressor stage into the
&@
http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=16http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=17http://en.wikipedia.org/wiki/SR-71_Blackbirdhttp://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58http://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=16http://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=17http://en.wikipedia.org/wiki/SR-71_Blackbirdhttp://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58http://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58 -
5/20/2018 turbofan engine
39/47
Turbofan
afterburner$[3]* of the %!
(1
-
5/20/2018 turbofan engine
40/47
Turbofan
in the for. of li@uid
hydrogenit has a density one
fourteenth that of water$ It is
also deeply cryogenic and
re@uires /ery significant
insulation that precludes it
being stored in wings$ #he
o/erall /ehicle would end up
being /ery large: and difficult
for .ost airports to
acco..odate$ inally: pure
hydrogen is not found in
nature: and .ust be.anufactured either /ia
stea. refor.ing or e6pensi/e
electrolysis$ 9e/ertheless:
research is ongoing and
hydrogen!fueled aircraft
designs do e6ist that .ay be
feasible$
[edit]+recooled )etenginesMain article: Precooled jetengine
An idea originated by obert
+$ -ar.ichael in 1,55[31]is
that hydrogen!fueled engines
could theoretically ha/e .uchhigher perfor.ance than
hydrocarbon!fueled engines if
a heat e6changer were used
to cool the inco.ing air$ #he
low te.perature allows lighter
.aterials to be used: a higher
.ass!flow through the
engines: and per.its
co.bustors to in7ect .ore fuel
86
http://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=19http://en.wikipedia.org/wiki/Precooled_jet_enginehttp://en.wikipedia.org/wiki/Precooled_jet_enginehttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-30http://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/wiki/Liquid_hydrogenhttp://en.wikipedia.org/w/index.php?title=Jet_engine&action=edit§ion=19http://en.wikipedia.org/wiki/Precooled_jet_enginehttp://en.wikipedia.org/wiki/Precooled_jet_enginehttp://en.wikipedia.org/wiki/Jet_propulsion#cite_note-30 -
5/20/2018 turbofan engine
41/47
Turbofan
without o/erheating the
engine$
#his idea leads to plausible
designs li;e eaction Engines%A&E: that .ight
per.it single!stage!to!orbit
launch /ehicles:[32]and A#EM:
which could per.it 7et
engines to be used up to
hypersoni