For Training Purpose Only
DETAILED TRAINING
VAR Part 7 - Aircraft Maintenance Basic Cat B1+B2
TRAINING MANUAL
M15.06
Issue: 01
Rev: 00
Date: 25/04/2014
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Training Manual
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EJAMF
Gas Turbine Engine
MODULE 15
M15.06 GAS TURBINE SECTION
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M15 GAS TURBINE ENGINE
HAM US/F-4
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01.04.2008
ATA DOC
Page 1
EJAMF
Gas Turbine Engine
MODULE 15
PRINCIPLES OF OPERATION
TURBINE TYPES AND COMPONENTS
The turbine provides power which is necessary to drive the engine compressor
and the accessory gear box.
The turbine extracts energy from the hot gases which come from the
combustion chamber.
There are 2 different types of turbines on gas turbine engines:
S one is the radial flow turbine and
S the other one is the axial flow turbine.
The 2 types of turbine have the same main components.
The first main component of a turbine is always a set of stationary vanes.
These vanes are named the turbine nozzle guide vanes.
The next component is a set of moving rotor blades on the turbine disc.
You can find turbines with one or more stages. Like the stages of a
compressor, a turbine stage is made up of a stator and of a rotor.
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Figure 1
HAM US/F-4
SwD
01.04.2008
Turbine Types and Components
01|Turb Types&Comp/A/B1
Page 3
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Types and Components cont.
Radial flow turbines are always single stage turbines.
They are only used on small gas turbine engines like this APU in the graphic.
Their advantage is that they have a simple design and are easy to
manufacture.
Radial turbines have many disadvantages compared with axial flow turbines.
They only allow small airflows and are also less efficient. This is because of
high aerodynamic losses and because the airflow must pass through the
turbine against the opposing centrifugal forces.
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Figure 2
HAM US/F-4
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01.04.2008
Radial Flow Turbine
02|Turb Types&Comp/A/B1
Page 5
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Types and Components cont.
Axial flow turbines are mainly used on modern gas turbine engines.
They can be built up with any number of turbine stages as necessary to
operate
S the engine compressor,
S the accessories and
S the large fan of these high bypass turbofan engines.
Another advantage of axial turbines is that they allow the very high airflow
which is needed to create the high thrust of modern engines.
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Figure 3
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01.04.2008
Axial Flow Turbine
03|Turb Types&Comp/A/B1
Page 7
EJAMF
Gas Turbine Engine
MODULE 15
OPERATION OF A TURBINE
The turbine converts the gas energy from the combustion chamber into torque.
The gas flow which comes from the combustion chamber must first pass
through the stationary turbine nozzle guide vanes.
The gas flow from the combustion chamber is accelerated because of the
convergent shape of the ducts between the nozzles guide vanes and deflected
towards the direction of rotation of the turbine blades.
The impact of the gas flow on the turbine rotor blades causes the turbine to
rotate. This makes the torque to drive the turbine shaft.
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Figure 4
HAM US/F-4
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01.04.2008
Turbine Operation
04|Operation Turb/A/B1
Page 9
EJAMF
Gas Turbine Engine
MODULE 15
Operation of a Turbine cont.
A turbine which makes the rotation only by the impact of the gas flow on the
rotor blades is named impulse turbine.
You can recognize this turbine type by the special shape of the rotor blades.
If you also compare the inlet area between the rotor blades with the outlet area,
you can see that they are the same size. This means that the gas flow in an
impulse turbine only pushes the rotor blades and then leaves the rotor.
You usually only find impulse turbines on very old gas turbine engines.
Next you will see how this turbine design is further improved.
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Figure 5
HAM US/F-4
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01.04.2008
Impulse Turbine
05|Operation Turb/A/B1
Page 11
EJAMF
Gas Turbine Engine
MODULE 15
Operation of a Turbine cont.
There are turbine rotor blades of modern gas turbine engines shown in the
graphic.
You can see here that the inlet of the rotor looks the same as an impulse type,
but the outlet of the rotor is shaped like a nozzle.
The gas flow from the nozzle guide vanes impacts on the rotor blades and at
the same time it accelerates as it passes through the nozzle shaped turbine
rotor channels.
The acceleration of the gas flow in the rotor creates a thrust force at the rotor
outlet.
The force at the turbine rotor outlet acts in the opposite direction to the
discharging gas flow. It is created as a reaction to the accelerated gas flow.
This reaction force can be divided into a vector that acts in an axial direction
and into a vector that acts in the direction of rotation.
This type of turbine is named the impulse−reaction turbine because the force
which operates the turbine is the sum of the force caused by the impulse of the
gas flow on the rotor blades and of the force caused by the reaction of the gas
flow which leaves the rotor stage.
The impulse−reaction turbine is often just called a reaction turbine.
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Figure 6
HAM US/F-4
SwD
01.04.2008
Reaction Turbine
06|Operation Turb/A/B1
Page 13
EJAMF
Gas Turbine Engine
MODULE 15
TURBINE OPERATING ENVIRONMENT
Turbines must operate in a very extreme environment.
The loads carried by the turbine components determine how long they can
remain in service. Turbine materials must withstand extremely high
temperatures and very high centrifugal forces due to high rotational speeds.
There are 2 more factors which reduce the service life of a turbine:
S The first one is material fatigue, which is caused by many power cycles. It
can only be reduced by correct engine operation.
S The other factor is corrosion which is caused by sulphuric acid. This mainly
occurs because of the sulphur in fuel and high gas temperatures. It is only
prevented by using the correct kind of jet fuel.
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Figure 7
HAM US/F-4
SwD
01.04.2008
Turbine Operating Environment
07|Turb Op Envrm/A/B1
Page 15
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Operating Environment cont.
At take−off power each turbine blade must withstand high centrifugal forces of
several tons. Through these forces the blades become longer. This kind of
deformation is increased by the heat in the turbine.
However, during normal engine operation this deformation remains elastic. This
means that the rotor blades return to their original shape when the loads are
gone.
Material deformation known as creep occurs when centrifugal loads are applied
over a long period of time and especially with high material temperatures.
This kind of deformation does not return to the original shape when the loads
are removed.
At normal engine operation very little or no creep occurs, but if the engine is
operated at maximum power, the creep starts.
The combined effect of high engine speed and high temperatures results in a
large increase in the rate of creep.
Because of this danger, the pilot must keep the maximum power setting for
short amounts of time only.
As a result we can say that creep is a function of centrifugal force, material
temperature and time.
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Figure 8
HAM US/F-4
SwD
01.04.2008
Creep
08|Turb Op Envrm/A/B1
Page 17
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Operating Environment cont.
There are 2 opposing factors that make it hard to prevent material deformation.
For example, we need high turbine inlet temperatures for optimum internal
efficiency, but we also need low turbine material temperatures to prevent
plastic deformation.
Because of these factors, plastic deformation can only be limited by efficient
cooling of the turbine materials.
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Figure 9
HAM US/F-4
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01.04.2008
Opposing Factors of Turbine Operation
09|Turb Op Envrm/A/B1
Page 19
EJAMF
Gas Turbine Engine
MODULE 15
TURBINE COOLING METHODS
There are 2 main reasons why turbines are cooled on modern engines.
Firstly they are cooled to increase their service life. This is done by cooling the
internal turbine components like nozzle guide vanes and rotor blades.
The second reason for cooling is to get a better turbine efficiency. This is done
by cooling the outer turbine casings.
The cooling of the inner turbine materials is necessary where the gas
temperatures are too high.
The high pressure turbine nozzle guide vanes and rotor blades are cooled with
air from the engine high pressure compressor.
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Figure 10
HAM US/F-4
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01.04.2008
Turbine Cooling Methods
10|Turb Coolg Meth/A/B1
Page 21
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Cooling Methods cont.
Different cooling methods are used in high pressure turbines.
Convection cooling is the easiest method.
Here the cooling airflow passes through the hollow turbine nozzle vanes and
rotor blades.
Convection cooling takes away the heat from the turbine materials while the air
passes along the inner walls of the turbine airfoils.
This cooling method is used at the turbine nozzle guide vanes and also at the
turbine rotor blades.
The cooling air enters through holes at the bottom of the rotor blades and flows
through the many internal channels.
The air finally escapes at the trailing edges and at the blade tips and mixes with
the hot gas flow.
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Figure 11
HAM US/F-4
SwD
01.04.2008
Convection Cooling
11|Turb Coolg Meth/A/B1
Page 23
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Cooling Methods cont.
Impingement cooling is a better cooling method for turbine nozzle guide vanes
and rotor blades.
Here the cooling air first flows into an insert which is fixed inside the hollow
turbine airfoils.
The insert has many small holes which serve as jet nozzles.
The cooling air that is forced through these jet nozzles impacts on the inner
walls of the airfoils. This improves the contact between cooling air and turbine
materials and therefore the heat transfer.
The cooling airflow finally escapes at the trailing edges of the nozzle guide
vanes and mixes with the hot gas flow.
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Gas Turbine Engine
MODULE 15
Inserts
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Figure 12
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Impingement Cooling
12|Turb Coolg Meth/A/B1
Page 25
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Cooling Methods
The film cooling method is a further cooling improvement.
This method is used at the turbine nozzle guide vanes and at the rotor blades.
Cooling air is blown into the hot gas flow via small drill holes in the turbine
airfoils.
The gas stream deflects the cooling air and forms a thin air film on the outer
walls of the turbine blades and vanes. This cooling film prevents the direct
contact of hot gas flow with turbine materials.
Film cooling is the most effective method because it reaches a maximum
cooling effect but with a minimum of cooling air. This means that more air is
available to drive the turbine.
The disadvantage of this cooling method is that these small drill holes are very
difficult to make and therefore very expensive.
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MODULE 15
Cooling Air
Holes
Figure 13
HAM US/F-4
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Film Cooling
13|Turb Coolg Meth/A/B1
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Gas Turbine Engine
MODULE 15
Turbine Cooling Methods cont.
On most modern gas turbine engines you will normally find a combination of all
3 cooling methods.
But keep in mind that this kind of turbine cooling is only necessary for high
pressure turbines which operate in high gas temperatures.
The first stage nozzle guide vanes are cooled because of the very high gas
temperatures from the combustion chamber by.
S convection,
S impingement and by
S film cooling
The first stage rotor blades are cooled because of the very high gas
temperatures by:
S convection,
S impingement and by
S film cooling
Impingement cooling is not always used by all engine manufacturers.
The second stage nozzle guide vanes are normally cooled by
S convection and
S impingement.
This is possible because the gas temperatures at this stage are much lower
than at the turbine inlet.
The second stage rotor blades are because of the lower gas temperatures
normally cooled by:
S convection only
The combination of these cooling methods gives a good balance between
manufacturing costs, turbine efficiency and service life.
HAM US/F-4
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14|Turb Coolg Meth/A/B1
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Figure 14
HAM US/F-4
SwD
01.04.2008
HPT Cooling
14|Turb Coolg Meth/A/B1
Page 29
EJAMF
Gas Turbine Engine
MODULE 15
TURBINE CLEARANCE CONTROL
Modern gas turbine engines have active clearance control systems.
These systems keep the tip clearance as small as possible in all operating
conditions.
The tip clearance is the gap between the tip of a rotor blade and the casing of
the respective compressor or turbine.
If during operation this tip clearance becomes too small, the rotor blades can
make contact with the turbine casing. This causes wear on the turbine
materials or it can completely damage the turbine.
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Figure 15
HAM US/F-4
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01.04.2008
Tip Clearance
15|Turb Clear Control/A/B1
Page 31
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Clearance Control cont.
Tip clearances change with the operational condition of the engine.
A large tip clearance decreases the efficiency of a turbine stage because a
large amount of gas passes through the gap between the rotor blades and
turbine casing. This part of the gas flow does not drive the turbine. This means
additional fuel is necessary to keep the desired turbine rotor speed.
Example: High pressure turbine of the CFM 56−5 engine with a clearance
control system.
Tests have shown that if the tip clearance gets bigger by 0.25mm or 0.01inch,
then the specific fuel consumption increases by 1%.
An increase of 1% in fuel consumption can result in approximately 30000kg of
extra fuel per year for 1 engine.
Note that without a clearance control system the increase in fuel consumption
on this engine becomes 4 times higher than with a clearance control system.
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Figure 16
HAM US/F-4
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01.04.2008
Effects of Tip Clearance Changes
16|Turb Clear Control/A/B1
Page 33
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Clearance Control cont.
Tip clearances change because of the different expansion of engine materials.
You know that all materials expand if they become warmer.
The amount that a material expands depends mainly on the temperature
differences by which it is heated and it depends on the size of the material.
This is because the expansion is always a percentage of the original size.
The time taken for the material to expand depends mainly on the thickness of
the material. Thin materials are heated up much faster.
This means that thin materials expand much faster than thick materials.
At engine start, high gas temperatures act on the turbine materials. The turbine
casing expands faster than the turbine rotor because of 2 reasons: it is thinner
than the rotor and it is in contact with higher temperatures.
The same kind of expansion also happens when the engine accelerates from
low speeds to high speeds.
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Figure 17
HAM US/F-4
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01.04.2008
Material Expansion
17|Turb Clear Control/A/B1
Page 35
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Clearance Control cont.
However, when rotor speeds get faster, the centrifugal forces on the rotor
increase.
These centrifugal forces reduce the tip clearance because the rotor disc and
blades expand further.
Note that the expansion of a material by centrifugal force is much bigger than
expansion caused by heat. This means that the tip clearance is much bigger on
low engine speeds than high engine speeds.
If the engine is shut down, the diameter of the turbine rotor and of the casing
decreases.
At engine deceleration or shut down, the tip clearance changes as follows:
S First the rotor shrinks faster than the turbine casing because of the
decreasing centrifugal forces.
S Afterwards the turbine casing shrinks faster because of the thinner casing
materials.
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Figure 18
HAM US/F-4
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01.04.2008
Relation between Engine Speed and Tip Clearance
18|Turb Clear Control/A/B1
Page 37
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Gas Turbine Engine
MODULE 15
Turbine Clearance Control cont.
Modern gas turbine engines have so called active clearance control systems.
These systems keep the tip clearance as small as possible in all operating
conditions.
Cold fan air is normally used to cool the turbine casings. On other engines
compressor bleed air is used instead of fan air.
These tip clearance control systems become more important on modern
engines.
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Fan Air
Compressor Air
Figure 19
HAM US/F-4
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01.04.2008
Air for Active Clearance Control
19|Turb Clear Control/A/B1
Page 39
EJAMF
Gas Turbine Engine
MODULE 15
TURBINE CLEARANCE CONTROL SYSTEM
INTRODUCTION
Tip clearances change during normal engine operation.
Modern aircraft engines therefore have clearance control systems that can
keep the tip clearance at an optimum during all operating conditions.
Depending on the method of air supply we differentiate between passive
clearance control and active clearance control.
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Figure 20
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Tip Clearance Change
01|Intro/A/B1
Page 41
EJAMF
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MODULE 15
Introduction cont.
The passive clearance control method is used on some engines for the HP and
for the LP turbine.
Here the turbine cases are cooled by a continuous airflow that is not regulated.
Passive clearance control for the HP turbine uses air from the last stages of
the HP compressor as the cooling source.
This air passes through oversize bolt holes, slots and other flow passages in
the case of the HP turbine until it finally enters the gas flow path of the LP
turbine.
Passive clearance control for the LP turbine uses fan air as the cooling source.
The air is picked up at the fan discharge duct and sprayed on the LP turbine
case.
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Fan Airflow
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Figure 21
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Passive Clearance Control
02|Intro/A/B1
Page 43
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MODULE 15
Introduction cont.
Active clearance control systems use the same cooling air as passive
clearance control systems but they can control the quantity of air.
Many engines use fan air for the LP turbine and HP turbine.
Other engines use fan air for the LP turbine only and HP compressor bleed air
for the HP turbine.
If HP compressor bleed air is used for clearance control, it either comes from
the intermediate stages or from the last stages of the HP compressor.
In some operating conditions a mixture of cooling air from the two pick−ups is
used.
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HAM US/F-4
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01.04.2008
03|Intro/A/B1
Page 44
EJAMF
Gas Turbine Engine
MODULE 15
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Figure 22
HAM US/F-4
SwD
01.04.2008
Active Clearance Control
03|Intro/A/B1
Page 45
EJAMF
Gas Turbine Engine
MODULE 15
TURBINE CLEARANCE CONTROL COMPONENTS
A clearance control system has very few parts. It always has one or more
cooling air supply ducts that carry the cooling air to the turbine cases.
At the turbine cases there are manifolds that distribute the air to individual tube
assemblies on the turbine cases.
These tube assemblies are also called spray rings. They have many bleed
holes on their inner diameter.
The LPT cooling tubes are usually circular shaped tubes. The bleed holes are
pointing directly to the turbine case.
The HPT cooling tubes are often rectangular shaped tubes. On these tubes the
bleed holes are at the edges. This is important because they blow the cooling
air to the areas with the thickest materials first and make sure that the turbine
case expands and shrinks evenly.
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04|Turb Clear Control Comp/A/B1
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TURBINE SECTION
TURBINE CLEARANCE CONTROL
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EJAMF
Gas Turbine Engine
MODULE 15
Spray Tube
Bleed Holes
Bleed Holes
FOR TRAINING PURPOSES ONLY!
HPT Cooling Tube
Figure 23
HAM US/F-4
SwD
01.04.2008
Cooling Tubes
04|Turb Clear Control Comp/A/B1
Page 47
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Clearance Control Components cont.
Active clearance control systems also have one or more clearance control
valves.
They are just shut−off valves on older engines, but they are usually modulating
valves on modern engines.
The clearance control valves are always separate valves for the HP turbine and
the LP turbine.
They are usually in different locations as shown on the engine on the top right
or they are combined in a common valve housing as shown on the top left
engine.
The clearance control valves are controlled by the engine control unit and
actuated by fuel pressure from the hydromechanical unit (HMU).
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TURBINE CLEARANCE CONTROL
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EJAMF
Gas Turbine Engine
MODULE 15
Clearance Control Valve
(Shut-off)
Figure 24
HAM US/F-4
SwD
01.04.2008
Clearance Control Valve and System
05|Turb Clear Control Comp/A/B1
Page 49
EJAMF
Gas Turbine Engine
MODULE 15
ACTIVE TURBINE CLEARANCE CONTROL OPERATION
The diagram shows how the tip clearance changes with different operating
conditions on a HP turbine without clearance control.
The upper curve shows the case diameter and the lower curve the rotor
diameter so that the area in between the curves shows the tip clearance.
Tip clearance control saves a lot of fuel.
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01.04.2008
06|Act Turb Cl Contr Oper/A/B1
Page 50
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Gas Turbine Engine
MODULE 15
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Figure 25
HAM US/F-4
SwD
01.04.2008
Diagram Tip Clearance
06|Act Turb Cl Contr Oper/A/B1
Page 51
EJAMF
Gas Turbine Engine
MODULE 15
Active Turbine Clearance Control Operation cont.
On engines with a hydromechanical control unit the active clearance control
system operates only during climb and cruise because the tip clearance control
is most effective if the engine operates at high power for long time periods.
Further control is not possible with a hydromechanical control unit because of
its limited capabilities.
A hydromechanical engine control unit uses 2 signals to activate the clearance
control system.
It needs the core engine speed because cruise power operation is usually in
the range of 80 to 95% N2 and it needs the aircraft altitude from the engine
inlet pressure port.
With these 2 signals it opens or closes the clearance control valves.
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07|Act Turb Cl Contr Oper/A/B1
Page 52
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Gas Turbine Engine
MODULE 15
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Figure 26
HAM US/F-4
SwD
01.04.2008
Hydromechanical Tip Clearance Control
07|Act Turb Cl Contr Oper/A/B1
Page 53
EJAMF
Gas Turbine Engine
MODULE 15
Active Turbine Clearance Control Operation cont.
On engines with a FADEC system the tip clearance can be controlled for all
operating conditions.
This further improves fuel saving and makes sure that during acceleration the
tip clearances do not become too small.
The improved tip clearance control is possible because the ECU continuously
determines the actual tip clearance and calculates and controls the necessary
cooling air for the turbine cases.
The ECU uses many signals from the engine to calculate the rotor size and
case size and therefore also the tip clearance.
These signals differ from engine type to type. They are, for example:
S the rotor speeds N1 and N2,
S the turbine case temperature,
S the compressor discharge temperature,
S the compressor inlet temperature,
S the total air temperature and
S the exhaust gas temperature.
With the calculated tip clearance the ECU determines the necessary cooling
air.
It then sends control signals to the torque motors at the clearance control
valves and receives the feedback signals about the valve positions from the
position sensors.
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01.04.2008
08|Act Turb Cl Contr Oper/A/B1
Page 54
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Gas Turbine Engine
MODULE 15
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Figure 27
HAM US/F-4
SwD
01.04.2008
Tip Clearance Control on FADEC Engines
08|Act Turb Cl Contr Oper/A/B1
Page 55
EJAMF
Gas Turbine Engine
MODULE 15
CONSTRUCTION
OVERVIEW
The turbine section of a typical twin spool engine has
S a high pressure turbine (HPT),
S a low pressure turbine (LPT)
S and a turbine frame.
The high pressure turbine is surrounded by the high pressure turbine case.
The high pressure turbine rotor is fitted to the high pressure compressor rear
shaft. High pressure turbines are usually single or dual stage turbines.
The low pressure turbine is surrounded by the low pressure turbine case. The
turbine rotor is fitted to the low pressure turbine shaft. This shaft connects the
LPT rotor with the low pressure compressor rotor.
The turbine frame is behind the low pressure turbine. It carries the bearing
loads of the aft end of the low pressure turbine and transmits these loads to the
rear engine mount on the turbine frame.
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01|Overview/A/B1
Page 56
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Figure 28
HAM US/F-4
SwD
01.04.2008
Turbine Section Overview
01|Overview/A/B1
Page 57
EJAMF
Gas Turbine Engine
MODULE 15
STATOR ASSEMBLY
A typical turbine stator assembly has the following components:
− the stator case,
− the nozzle guide vanes,
− sealing− and wall segments,
− and clearance control air manifolds.
The case of this high pressure turbine is bolted to the rear flange of the
combustion case. The case supports the nozzle guide vanes and the wall
segments opposite of the rotor blades.
High pressure turbine cases are usually made in 1 piece.
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02|Stator Assem/A/B1
Page 58
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Figure 29
HAM US/F-4
SwD
01.04.2008
HPT Stator Assembly Main Components
02|Stator Assem/A/B1
Page 59
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
In the graphic you can see the wall segments in the turbine case.
These segments have an abradable ceramic surface, which gives optimum
thermal resistance, but it can wear off easily when in contact with the tips of the
turbine rotor blades.
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MODULE 15
Wall Segments
Stage 1
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Figure 30
HAM US/F-4
SwD
01.04.2008
Wall Segments
03|Stator Assem/A/B1
Page 61
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
The nozzle guide vanes of the high pressure turbine are held in place by the
nozzle guide vane support, which is attached to the combustion case or to the
turbine case.
These nozzle guide vanes are made of many vane segments. Each vane
segment usually has 2 nozzle guide vanes.
The gaps between the vane segments are sealed with metallic sealing strips
which fit into slots in the outer and inner platform of the nozzle guide vane.
The nozzle guide vanes of the second high pressure turbine stage are behind
the first turbine rotor stage. They are fitted into slots on the inner surface of the
high pressure turbine case. They are also usually made of segments with 2
vanes.
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Page 62
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Figure 31
HAM US/F-4
SwD
01.04.2008
HPT 1st Stage Nozzle Guide Vanes
04|Stator Assem/A/B1
Page 63
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
On the inner ring of the segments you will find a sealed surface which belongs
to an airseal. In this position the airseal is known as the interstage seal.
The interstage seal prevents gas flow through the gap between the stator and
the rotor. This is similar to the arrangement for the compressor.
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Figure 32
HAM US/F-4
SwD
01.04.2008
HPT 2nd Stage Nozzle Guide Vanes
05|Stator Assem/A/B1
Page 65
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
On modern turbofan engines there are cooling air tubes around the high
pressure turbine case. These tubes are used for the active clearance control
system.
The clearance control system feeds cold air to the outer surface of the case to
minimize the tip clearance between the turbine rotor blades and the stator
case.
There are borescope ports in the turbine case for inspecting the rotor blades.
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Gas Turbine Engine
MODULE 15
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Cooling Air Tubes
Figure 33
HAM US/F-4
SwD
01.04.2008
HPT Case Cooling Air Tubes
06|Stator Assem/A/B1
Page 67
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
Now we will take a look at a stator case of a typical low pressure turbine. This
case is bolted to the rear flange of the high pressure turbine.
It supports the nozzle guide vanes of the low pressure turbine and its outer
airseals. These outer airseals form a labyrinth seal with the knife edges of the
rotor blades.
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Figure 34
HAM US/F-4
SwD
01.04.2008
LPT Stator Case
07|Stator Assem/A/B1
Page 69
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
You usually find that low pressure turbine cases are made of 1 piece on most
modern engines. But you can also find split stator cases on some engines as
shown in the left graphic.
You can see the arrangement of the nozzle guide vanes and the outer airseals
in the case.
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MODULE 15
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Inner Air Seals
Figure 35
HAM US/F-4
SwD
01.04.2008
LPT Case Components
08|Stator Assem/A/B1
Page 71
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
The inner air seals are located on the inner surface of the nozzle guide vane
segments. In the low pressure turbine these segments are made of 6 or 7
vanes. They are fitted to the case by the rims on the outer platform.
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MODULE 15
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Rim
Figure 36
HAM US/F-4
SwD
01.04.2008
LPT Vane Segments
09|Stator Assem/A/B1
Page 73
EJAMF
Gas Turbine Engine
MODULE 15
Stator Assembly cont.
Similar to the high pressure turbine the low pressure turbine case has cooling
air tubes for the active clearance control system.
There are also some borescope ports for the internal inspection of the low
pressure turbine rotor blades.
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Figure 37
HAM US/F-4
SwD
01.04.2008
LPT Case Components
10|Stator Assem/A/B1
Page 75
EJAMF
Gas Turbine Engine
MODULE 15
ROTOR ASSEMBLY
The high pressure turbine rotor is attached to the compressor rear shaft behind
the rear bearing.
The high pressure turbine rotor has the following main components:
S the turbine discs,
S the rotor blades,
S a rotating interstage seal,
S and forward and rear blade retainers.
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11|Rotor Assem/A/B1
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EJAMF
Gas Turbine Engine
MODULE 15
Interstage
Seal
Rear Blade
Retainer
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Forward
Blade Retainer
Stage 1 Disc
Figure 38
HAM US/F-4
SwD
01.04.2008
Stage 2 Disc
HPT Rotor Main Components
11|Rotor Assem/A/B1
Page 77
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
The turbine discs hold the rotor blades and transfer the torque from the blades
to the compressor rear shaft.
The cross−sectional area of the turbine discs is very large. This is necessary
because the disc must withstand high centrifugal loads from the blades in high
operating temperatures.
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Figure 39
HAM US/F-4
SwD
01.04.2008
HPT Rotor Discs
12|Rotor Assem/A/B1
Page 79
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
The interstage seal acts as a spacer between the 2 discs.
On some high pressure turbines this seal must also transfer some torque from
the stage 2 disk to the stage 1 disk.
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MODULE 15
Interstage Seal
Figure 40
HAM US/F-4
SwD
01.04.2008
HPT Rotor with Interstage Seal
13|Rotor Assem/A/B1
Page 81
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
The blade retainers are designed to hold the turbine blades in place so that
they do not move from their seats due to the gas loads.
These retainers are often ring elements that are fixed to the rotor discs.
The retainers usually have seal lips which act as an airseal. Sometimes you
may find that the airseal is a blade retainer.
There are strip-type blade retainers in low pressure turbines. They fit into the
dovetail slots and are then bent up at each end.
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MODULE 15
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Blade Retainer
Blade Retainer
Figure 41
HAM US/F-4
SwD
01.04.2008
HPT Rotor Blade Retainer
14|Rotor Assem/A/B1
Page 83
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
Now let us look at the rotor blades on the high pressure turbine rotor. The rotor
blade has a special shaped root. This type of root is known as a fir tree root
because of its shape.
The fir tree root has many contact surfaces, so that the forces from the blade
are smoothly transmitted to the disc. This leads to a longer service life for the
rotor components.
Usually the blades are loose in their fir tree seats when the turbine is at rest.
But when the turbine rotates, the blades are forced into their seats by the
centrifugal loads.
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Figure 42
HAM US/F-4
SwD
01.04.2008
HPT Rotor Blade Root
15|Rotor Assem/A/B1
Page 85
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
Two types of turbine blades are used in modern gas turbine engines. These are
open end blades and shrouded blades.
Open end turbine blades are mainly used in turbines with high rotational
speeds such as high pressure turbines.
You may also find shrouded turbine blades in some high pressure turbines.
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Figure 43
HAM US/F-4
SwD
01.04.2008
Different Type of HPT Blades
16|Rotor Assem/A/B1
Page 87
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
Shrouded blades form a band around the tips of the rotor blades. These
shrouds help to reduce any vibrations.
These blades also have a knife edge seal around the outer surface of the
shroud. This seal helps to reduce air losses at the tip of the blades.
A disadvantage of the shroud on the turbine blade is that it adds more weight
to each rotor blade.
So as result of this, shrouded blades are mainly used in low pressure turbines
with lower rotational speeds. In these turbines the added weight of the tip
shroud is offset by thinner blades, which are also more efficient.
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MODULE 15
Tip Shroud
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Shrouded HPT Blades
Figure 44
HAM US/F-4
SwD
01.04.2008
Shrouded Blades
17|Rotor Assem/A/B1
Page 89
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
The turbine discs are either directly splined to the drive shaft as shown in this
high pressure turbine graphic or they are bolted together and connected to a
common drive shaft as you can see on the low pressure turbine.
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Figure 45
HAM US/F-4
SwD
01.04.2008
Turbine Discs
18|Rotor Assem/A/B1
Page 91
EJAMF
Gas Turbine Engine
MODULE 15
Rotor Assembly cont.
High pressure turbine blades are internally cooled by air from the high pressure
compressor.
If you take a closer look at the installed turbine blades, you can see a gap
between the lower end of the blade root and the lower end of the fir tree slot.
The cooling air enters the rotor blade through this gap.
The cooling air can be fed into this gap from the front or from the rear of the
turbine disc.
On other turbines the air enters the gap through internal air passages in the
turbine disc as you can see in the cross−sectional view.
The air finally flows into the turbine blade through the holes in the bottom
surface of the blade root.
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Figure 46
HAM US/F-4
SwD
01.04.2008
HPT Blade Internal Cooling
19|Rotor Assem/A/B1
Page 93
EJAMF
Gas Turbine Engine
MODULE 15
TURBINE FRAME
The turbine frame is the aft major structural component of the engine. The
frame supports the turbine rotors. Depending on the engine, 1 or 2 rotors can
be supported by the frame.
The second function of the turbine frame is to provide attachment points for the
rear engine mount.
It also supports the engine exhaust components like the jet nozzle and the
exhaust cone.
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Figure 47
HAM US/F-4
SwD
01.04.2008
Turbine Frame Function
20|Frame/A/B1
Page 95
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Frame cont.
A typical turbine frame is built up of
S a frame hub with the bearing support,
S an outer frame casing
S and a set of struts which connect the hub with the outer casing.
The frame struts are the same as those used in the fan frame or in the
compressor rear frame.
You usually find that the struts of the turbine frame are aerodynamically shaped
to cause as little drag as possible to the exhaust gas flow. They are also hollow
inside. This design gives room for oil supply lines, scavenge lines and oil drain
lines and also gives higher structural strength against bending and torsion.
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TURBINE SECTION
CONSTRUCTION
HAM US/F-4
SwD
01.04.2008
21|Frame/A/B1
Page 96
Lufthansa Technical Training
TURBINE SECTION
CONSTRUCTION
EJAMF
Gas Turbine Engine
MODULE 15
Oil Supply
Line
FOR TRAINING PURPOSES ONLY!
Frame Strut
Figure 48
HAM US/F-4
SwD
01.04.2008
Turbine Frame Build Up
21|Frame/A/B1
Page 97
EJAMF
Gas Turbine Engine
MODULE 15
Turbine Frame cont.
If you look at the frame in flight direction, you can see the arrangement of the
frame struts. There are 2 different arrangements of frame struts on gas turbine
engines.
There are radial struts like those you saw on the fan frame. Radial struts are
usually designed as short as possible. This minimizes the expansion of the
struts and keeps the stress on the frame hub low.
There are also tangential struts. Tangential struts minimize the stress caused
by thermal expansion because if they expand, they will cause the hub to rotate
slightly.
FOR TRAINING PURPOSES ONLY!
Lufthansa Technical Training
TURBINE SECTION
CONSTRUCTION
HAM US/F-4
SwD
01.04.2008
22|Frame/A/B1
Page 98
EJAMF
Gas Turbine Engine
MODULE 15
FOR TRAINING PURPOSES ONLY!
Lufthansa Technical Training
TURBINE SECTION
CONSTRUCTION
Figure 49
HAM US/F-4
SwD
01.04.2008
Turbine Frame Struts
22|Frame/A/B1
Page 99
EJAMF M15.06 B1 E
TABLE OF CONTENTS
M15.06 GAS TURBINE SECTION . . . . . . . . . . . . .
1
PRINCIPLES OF OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TURBINE TYPES AND COMPONENTS . . . . . . . . . . . . .
OPERATION OF A TURBINE . . . . . . . . . . . . . . . . . . . . . .
TURBINE OPERATING ENVIRONMENT . . . . . . . . . . . .
TURBINE COOLING METHODS . . . . . . . . . . . . . . . . . . . .
TURBINE CLEARANCE CONTROL . . . . . . . . . . . . . . . . .
2
2
8
14
20
30
TURBINE CLEARANCE CONTROL SYSTEM . . . . . . . . . . . . . . . . . . .
40
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
TURBINE CLEARANCE CONTROL COMPONENTS . .
46
ACTIVE TURBINE CLEARANCE CONTROL OPERATION . . . . . .
50
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
STATOR ASSEMBLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ROTOR ASSEMBLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TURBINE FRAME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
56
58
76
94
Page i
EJAMF M15.06 B1 E
TABLE OF CONTENTS
Page ii
EJAMF M15.06 B1 E
TABLE OF FIGURES
Figure
Figure
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Figure
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Figure
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Turbine Types and Components . . . . . . . . . . . . . . . . . . . . . . . . .
Radial Flow Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Axial Flow Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbine Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Impulse Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reaction Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbine Operating Environment . . . . . . . . . . . . . . . . . . . . . . . . . .
Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Opposing Factors of Turbine Operation . . . . . . . . . . . . . . . . . . .
Turbine Cooling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Convection Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Impingement Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Film Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tip Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Effects of Tip Clearance Changes . . . . . . . . . . . . . . . . . . . . . . .
Material Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Relation between Engine Speed and Tip Clearance . . . . . . .
Air for Active Clearance Control . . . . . . . . . . . . . . . . . . . . . . . .
Tip Clearance Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Passive Clearance Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Active Clearance Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cooling Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clearance Control Valve and System . . . . . . . . . . . . . . . . . . . .
Diagram Tip Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hydromechanical Tip Clearance Control . . . . . . . . . . . . . . . . .
Tip Clearance Control on FADEC Engines . . . . . . . . . . . . . . .
Turbine Section Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Stator Assembly Main Components . . . . . . . . . . . . . . . .
Wall Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT 1st Stage Nozzle Guide Vanes . . . . . . . . . . . . . . . . . . . . .
HPT 2nd Stage Nozzle Guide Vanes . . . . . . . . . . . . . . . . . . . .
HPT Case Cooling Air Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . .
LPT Stator Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LPT Case Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
51
53
55
57
59
61
63
65
67
69
71
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
36
37
38
39
40
41
42
43
44
45
46
47
48
49
LPT Vane Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LPT Case Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Rotor Main Components . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Rotor Discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Rotor with Interstage Seal . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Rotor Blade Retainer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Rotor Blade Root . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Different Type of HPT Blades . . . . . . . . . . . . . . . . . . . . . . . . . .
Shrouded Blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbine Discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HPT Blade Internal Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbine Frame Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbine Frame Build Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbine Frame Struts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
75
77
79
81
83
85
87
89
91
93
95
97
99
Page i
EJAMF M15.06 B1 E
TABLE OF FIGURES
Page ii
EJAMF M15.06 B1 E
TABLE OF FIGURES
Page iii
EJAMF M15.06 B1 E
TABLE OF FIGURES
Page iv