ae3212 aircraft gas turbine components

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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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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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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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 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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Typical annular type Typical can-annular type


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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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Turbine Types1. Impulse Turbine2. Reaction Turbine

Impulse Reaction


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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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