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8/12/2019 AE3212 Aircraft Gas Turbine Components
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Contents : Aircraft Engine Components Station Numbering
Inlet Compressor Combustor Turbine Nozzle Thrust Augmentation
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Aircraft Engine Components
Main Components Thrust Augmentation
Engine Components
Inlet
Compressor
Combustor
TurbineNozzle
Afterburning
Water injection
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Aircraft Engine Components
Station Numbering for Gas Turbine Engines
Free Stream : 0
Inlet diffuser : 1 - 2Fan / Compressor : 2 - 3
LP Compressor : 2 2.5HP Compressor : 2.5 - 3
Combustor : 3 - 4
Turbine : 4 5
HP Turbine : 4 4.5LP Turbine : 4.5 - 5
After burner : 6 - 7
Nozzle : 7 8 9
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Aircraft Engine Components
Inlet/diffuser To bring the air from ambient conditions to the conditionsrequired at the inlet to the engine compressor.
How ? by a compression process increases the air pressure
Classification of InletSubsonic Inlet less compressed air Supersonic Inlet more compressed air due to shock wave
Important parameters for Operation and design of the inletEfficiency of Compression processExternal dragmass flow into the inlet
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Aircraft Engine ComponentsInlet/diffuser
To supply air to engine at theaxial Mach number
To capture the entering stream-tube over a wide range of freestream Mach number
To reduce pressure loss due to theexistence shock wave
To capture the entering stream-tubewith variation freestream Machnumbers from subsonic to supersonic
To control a sensitivity impuls andthrust to diffuser pressure recovery
Classification of Inlet/ diffuser
SupersonicSubsonic Divergent ductRampCenter body
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Aircraft Engine ComponentsInlet/diffuser Design and Operation of Inlet
Supersonic Inlet Diffuser Internal compression (convegent-divergent channel) External compression
Mixed compression
External compression
External compression diffuser at flightMach number below design value
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Aircraft Engine ComponentsInlet/diffuser Design and Operation of Inlet
Supersonic Inlet Diffuser Internal compression (convegent-divergent channel) External compression
Mixed compression
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Aircraft Engine ComponentsCompressor
To controls the pressure ratio and the mass flow.It has a dominant influence on the engines characteristics
By increasing the pressure of the air, the volume of airis reduced the fuel/air mixture will occur in a smallervolume.Combustion process and power extraction process canbe carried more efficiently
Classification of Compressor Centrifugal Compressor a smaller gas turbine engines
Axial Compressor aircraft engines
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Aircraft Engine ComponentsCentrifugal Compressor
Centrifugal compressor consist of three main parts:Impeller Diffuser Compressor Manifold
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Aircraft Engine ComponentsCentrifugal Compressor
Process Air enters the compressor near the hub of the impeller Air is then compressed by the rotational motion of theimpeller increasing the velocity of the air
Diffusing the air in the diffuser the velocity decreasesand increased pressureThe diffuser also straightens the flowThe manifold serves as a collector to feed the air intothe combustor
Compression ratio for single stage centrifugal compressor 4:1 or 5:1
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Aircraft Engine Components Axial Compressor
Air flows in an axial direction through a series ofrotating rotor blades andstationary stator vanes
Each set rotor blades and stator vanes a stageEach stage produces a small compression pressure ratio(1.1 :1 to 1.2 : 1) at a high efficiency
Cross-sectional areadecreases in directionof the air.
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Aircraft Engine Components Axial Compressor
Blade row in axial compressor:Inlet guide vanes (IGV), Rotor blades and Stator blades
1. Inlet guide vanes (IGV)to give the flow a swirl in the direction of rotor motion toreduce the flow velocity relative to the blade rotor,minimizing shock losses and to equalize the staticpressure rise in the rotor and the stator.
2. Rotor blades
to add energy to the flow and in the process givesangular momentum to it
3. Stator bladesto remove the angular momentum and to diffuse theflow to raise the pressure
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Aircraft Engine Components Axial Compressor
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Aircraft Engine ComponentsCombustor
To burn a mixture of fuel and airTo deliver the resulting gases to the turbine at a uniform temperature.The gas temperature is limited by the structural temperature of turbine
Ratio of total air to fuel 30 60
Types of Combustion Chambers :Can
Annular Can-annular
Burner designa minimum pressure lossa high efficiencyno tendency to blow out (flame out)
Can
Annular
Can-Annular
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Aircraft Engine ComponentsCombustor
Typical annular type Typical can-annular type
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Aircraft Engine ComponentsCombustor
Primary Zone Intermediate Zone Dilute Zone
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Aircraft Engine ComponentsTurbineTo generate power of engine by absorbing the hightemperature gas produced by a combustor.Energy kinetic from the gas is converted to shaft horsepower to drive compressor.
Nearly three-fourth of allthe energy is required todrive the compressor
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Aircraft Engine ComponentsTurbine
Blade row in Turbine:1. Nozzle vanes
to turn flow while dropping pressure and raising Mach number
2. Rotor bladesto turn the flow back to remove angular momentum put in by the vanes
3. Stator (additional)to enforce zero swirl at the exit
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Aircraft Engine ComponentsTurbine
Turbine Types1. Impulse Turbine2. Reaction Turbine
Impulse Reaction
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Aircraft Engine ComponentsTurbine
Impulse Turbine
Rotor The relative discharge velocity = the relative inlet velocityNo net change in pressure between rotor inlet and rotor outletStator Increase velocity and reduce the pressure
Reaction Turbine
Rotor The relative discharge velocity increasesPressure decreases in the passageStator
Only change the flow direction
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Aircraft Engine ComponentsNozzle
Nozzle Types Convergent Convergent-Divergent Mixer
To accelerate the flow to a high velocity with minimumtotal pressure losses
o e u u m F
To control back pressure for matching exit andatmosphere pressure
Important Nozzle parametersNozzle Pressure ratioMach number exitRatio of Exit area to throat area
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Aircraft Engine ComponentsConvergent Nozzle
Used for Subsonic AircraftNozzle pressure ratio less than 2
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Aircraft Engine ComponentsConvergent-Divergent Nozzle
Used for Supersonic AircraftNozzle pressure ratio is greater than 2
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Aircraft Engine ComponentsConvergent-Divergent Nozzle
Ideally expanded nozzlep e = p o
Underexpanded nozzlep e > p o
Overexpanded nozzlep
e> p
o /2
Overexpanded nozzle
with separation
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Aircraft Engine ComponentsMixer Nozzle
Total Power = P core + P fan
Maximize Thrust can be reached when a given bypassing ratio( ) can provide u 6 = u 8 for separating core and fan nozzles
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Aircraft Engine ComponentsMixer NozzleFor actual Engine, the implementation of separate core and fannozzles tend to have higher core jet velocity than fan exitvelocity, i.e., u6 > u8.
Alternatively, to merge the two streams by mixing them anddischarging them through a single nozzle (mixer nozzle)
The mixing is irreversible process, resulting in an entropy increase
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Aircraft Engine ComponentsThrust Augmentation
Thrust augmentation is achieved by injecting water into eitherthe compressor or the combustor chamber.
When the water injected into the inlet of the compressor, the
mass flow increases and a higher combustion chamberpressure.Water injection on a hot day can increase take off thrust by
as much as 50%.
Water injection
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Aircraft Engine ComponentsThrust Augmentation
Thrust augmentation is achieved by burning additional fuel inthe afterburner.
The afterburner consist of the duct section, fuel injectors,
and flame holders.The effect of afterburning operation is to raise the
temperature of the exhaust gases which, when exhaust throughthe nozzle, will reach a higher exit velocity.
Afterburning
Without AB With AB
Thrust (lbf) 11.870 17.900
TSFC (lbm/hr/lbf)/hr 0.84 1.965
Engine J79 operating with afterburner
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Aircraft Engine ComponentsBrayton Cycle
1. Isentropic compression (2 to 3)2. Constant-pressure heat addition (3 to 4)3. Isentropic expansion (4 to 9)4. Constant-pressure heat rejection (9 to 2)
Heater
Cooler
Compressor Turbine
ou t Q
inQ
out W NetcW
mm
s
T
2
3
4
9
/)1(
3
2 111
PRT
T T
23 T T cmW pc 94 T T cmW pt
34 T T cmQ pin
29 T T cmQ pou t
2394 T T T T cmW W W
p
ct ou t Net
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Aircraft Engine ComponentsThermal Efficiency
/)1(
3
2 111
PRT
T T
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Aircraft Engine ComponentsNet Work output per unit massMaximum area within cycle on T-s diagram
2
2
42 1
T T
T cmW
pou t
Net
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Aircraft Engine ComponentsVariation of Brayton Cycle
1. Isentropic compression (2 to 3)2. Constant-pressure heat addition (3 to 4)3. Isentropic expansion (4, 5 to 9)4. Constant-pressure heat rejection (9 to 2)
/)1(
3
2 111
PRT
T T
2394 T T T T cmW W W
p
ct ou t Net
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Aircraft Engine ComponentsVariation of Brayton Cycle
1. Isentropic compression (2 to 3)2. Constant-pressure heat addition (3 to 4)3. Isentropic expansion (4 to 5 )4. Constant pressure reheat (5 to 7)
5. Constant-pressure heat rejection (9 to 2)
Increase the specific power Reduce the thermal efficiency
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