aerospace propulsion study for shenyang aerospace university by lale420 (final_eaxm_4 )

1 © Devinder K Yadav

Thrust Reversers

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Turbojet/turbofan Thrust Reversers

Aid in braking and directional control

during normal landings and Rejected

Take-Offs (RTOs)

Allow some aircraft to back out using

their own power

Reduce brake maintenance

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There are two types of thrust reverser used

• Cascade reversers (Aerodynamic Blockage)

• Clamshell reversers (Mechanical Blockage)

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Thrust Reversers

Clamshell reversers (Mechanical Blockage)

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Thrust Reversers

Cascade reversers (Aerodynamic Blockage)

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Clamshell reverser

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Clamshell Thrust Reverser

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Clamshell Thrust Reverser

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Cascade Reverser

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Cascade type

Thrust

Reversers

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Cascade Thrust Reverser

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Cascade Thrust Reverser

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Turbofan Thrust Reversers

Cascade & clamshell reverser

Cold stream reverser

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Reversers are angled forward enough to

give reverse thrust but not enough to

allow re-ingestion of exhaust gases

Reverse thrust is usually limited to speeds

above 60-70 knots to minimise foreign

object damage (FOD) ingestion

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To prevent reverse thrust

being accidentally engaged

while under forward power

interlocks allow thrust

reverser lever movement only

when the thrust level is at

idle.

Maintenance on thrust

reverser systems is high and

modern carbon brakes and

auto wheel braking systems

are minimising the use of

thrust reversers 17


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Thrust Reversers Safety Features

(Full Authority Digital Electronic Control) 21

Noise Suppression

Sources of Noise

• Intake Duct (acoustic panels installed in nose cowl to suppress this noise)

• Engine Housing

• Fan

• Compressor

• Exhaust Duct (Small eddies near the exhaust duct cause high frequency

noise and downstream larger eddies create low frequency noise).

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Noise Suppression

Exhaust duct noise

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Noise Suppression Exhaust duct noise

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Noise Suppression

Exhaust duct noise

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Noise Suppression

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Noise Suppression Devices

• Corrugated Perimeter noise suppressor • Multi-tube type noise suppressor.

Both types of suppressors break up the single, main jet exhaust stream into a number of smaller jet streams. This increases the total perimeter of the nozzle area and reduces the size of the eddies created as the gases are discharged into the open air. Although the total noise energy remains unchanged, the frequency is raised considerably.

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Corrugated Perimeter type Multi-tube type

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Noise absorbing lining material converts

acoustic energy into heat energy.

The liner material is matched to the

character of the noise for optimum

suppression.

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Noise

Suppression

Devices

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Thrust Augmentation Water Injection System

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Water Injection

Because thrust is proportional to:

Mass × Acceleration

it is affected by changes in the mass of air

passing through the engine.

Typically hot temperatures at a high

altitude aerodrome will mean reduced air

mass.

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Water Injection

The principle of latent heat of vaporisation

applies to the water injection process.

Water is injected into the compressor inlet

or the diffuser (sometimes both).

As the water evaporates it cools the air

around it.

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Water Injection

The heat transfer will reduce the

temperature of the air mass making the gas

flow more dense and increasing mass air

flow.

As the mass air flow increases it allows

more fuel to be used without exceeding

turbine temperature limits.

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Water Injection (System Operation

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Water Injection (System Operation)

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Water

Injection

System

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Water Injection System

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The water must be pure de-mineralised to

minimise the deposit of solids on turbine blades.

Methanol is added to act as an anti-freeze by

lowering the freezing point of the water.

A water methanol fluid means a single uplift can

be used for consecutive take-offs without

damage due to freezing.


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Water injection typically increases

thrust by 30%.

Care must be taken not to over-boost

the engine when switching water

injection on.


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Turbojet thrust restoration Turboprop power boost

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Afterburners

• More fuel added to exhaust and ignited

• Lots more thrust but very fuel inefficient • Greater requirement for variable area exhaust nozzle

On SST Concord; Afterburner used to take-off and accelerate from Mach 0.93 to Mach 1.7

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Afterburners

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Afterburners

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Afterburners

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Afterburners

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Afterburners

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Afterburners

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Turboprop Operation

Turboprops (and turboshafts) recover

energy from the hot gas stream and

convert it to mechanical energy

There are two types of powerplants

fixed shaft turbine

free shaft turbine 2

Turboprop Operation

Advantages of fixed turbine

Operate at a constant RPM (adding fuel

changes propeller pitch) so can optimise

internal aerodynamics

More immediate power response

More fuel efficient

Lighter

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Turboprop Operation

Advantages of free turbine

Low noise at ground idle

Easier engine start

Propeller can be stopped while the engine is

still operating

Propeller/gearbox vibrations aren’t

transmitted to the gas generator

Easy to disassemble for service

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Free Turbine

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Fixed Turbine

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Turboprop Operation

Both fixed and free turbines require a

speed reduction gearbox between the

turbine and the propeller

The gearbox converts low torque high

RPM to high torque low RPM

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Turboprop operation

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SAAB 2000 Flight Deck

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Turboprop Operation

Negative torque protection

An NTS is incorporated to reduce

windmilling drag and stop the propeller

driving the engine

A gas turbine compressor absorbs a large

amount of energy increasing propeller

drag of a windmilling propeller

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Turboprop Operation

NTS won’t feather the propeller

NTSing will occur until the pilot feathers

the propeller

NTS Lockout necessary to stop NTS occurring

on landing

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Beta Control

Turboprop operations can be broken into

two ranges of operation

Ground (range) operations

Flight (range) operations

A gate in the power lever operating range

separates the two ranges of operation

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Turboprop operations

Operations in ground range is known as

the Beta range

In flight range the propeller governor

controls the speed of the propeller

In Beta (ground) range the fuel control unit

automatically controls the engine RPM at a

preset value and movement of the power

lever controls blade angle 16

http://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.html

NASA engine simulator –

try it, you’ll like it

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aerospace propulsion study for shenyang aerospace university by lale420 (final_eaxm_4 )

Engineering