Module 3 (Cold Section) Flashcards
(174 cards)
1
Q
what are the main 5 sections of gas turbines?
A
combustion
turbine
exhaust
inlet duct
compressor
2
Q
the five major sections of gas turbines are grouped into two sections namely:
A
hot section
cold section
3
Q
A turbine engine’s hot section includes the____________, _______________, _________________
A
combustion, turbine, and exhaust sections.
4
Q
The
cold section includes the ______________ and _________________
A
air inlet duct and the compressor section
5
Q
it is built into the airframe or forward part of the nacelle installations
A
air inlet
6
Q
It is designed to provide a relatively turbulent free supply of air to the face
of the low pressure compressor or fan
A
Air inlet
7
Q
The design of the intake duct is vital to the performance of the engine under all airspeeds or angles of attack to avoid _______________
A
compressor stall
8
Q
The design of the ______________ is vital to the performance of the engine under all airspeeds or angles of attack to avoid compressor stall
A
intake duct
9
Q
It is designed to provide a
turbulence free supply of air to the first stage
compressor of the engine, with the minimum energy loss occurring through the inlet.
A
air intake
10
Q
To
enable the compressor to operate satisfactorily,
the air must reach the compressor at a _________________, distributed evenly across the whole of
the face of the first stage
A
uniform pressure
11
Q
The air inlet duct on a turbojet engine is
normally considered to be a part of the ______________
rather than the engine.
A
airframe
12
Q
Functions of the air inlet
A
- Recover as much of the total pressure
of the free airstream as possible and deliver this pressure to the compressor - Many inlets are shaped to raise the air
pressure above the atmospheric
pressure - Provide a uniform supply of air to the
compressor so the compressor can
operate efficiently
13
Q
Types of air inlet
A
- Pitot type intake
- Secondary Intake Doors
- Engine Mounted
- Wing Mounted
- Fuselage Mounted
- subsonic inlets
- supersonic inlets
- Bellmouth Inlets
14
Q
secondary intake doors is sometimes referred to as _____________________
A
auxillary inlet doors
15
Q
It allows a supplementary airflow to reach the compressor face during high power operation when that aircraft is either stationary or at low airspeeds
A
Secondary Intake doors
16
Q
It is an example of an aircraft which
must use high levels of engine power when it
has either zero or very low forward airspeed,
during vertical takeoff, hover, or landing
A
The Harrier
17
Q
It is an aircraft that incorporated Secondary intake doors
A
The harrier
18
Q
At airspeeds below which ram pressure recovery
can be achieved, the _____________– are held open by the depression in the intake.
A
auxiliary intake doors
19
Q
At higher forward speeds, when the pressure in the intake is greater than ambient, the _______________are shut by the pressure differential
which has been generated
A
auxiliary air intake doors
20
Q
At higher forward speeds, when the pressure in the intake is greater than ambient, the auxiliary air intake doors are shut by the _____________
which has been generated
A
pressure differential
21
Q
What are the example of aircraft that incorporates a combination of wing mounted and vertical stabilizer mounted engines
A
DC-10 and L-1011
22
Q
Several large commercial aircraft and large military aircraft use __________________.
A
wing mounted engines
23
Q
Some aircraft with engines mounted inside the wings feature air inlet ducts in the _______________
A
wing’s leading edge
24
Q
Aircraft such as the ____________________ all utilize wing-mounted inlets
A
Aerospatiale Caravelle,
de Havilland Comet
de Havilland Vampire
25
Engines mounted inside a fuselage typically use air inlet ducts located __________________
near the front of the fuselage
26
It is a process in which the air inlet recover as much of the total pressure of the free airstream as possible and deliver this pressure to the compressor.
Ram recovery or pressure recovery
27
many early military aircraft were designed with an air inlet duct in
the _________________
nose of the fuselage
28
It consists of a fixed
geometry duct whose diameter progressively
increases from front to back.
Subsonic Inlets
29
This ______________ in subsonic inlet works like a venturi in that as the intake air spreads out, the velocity of the air decreases
and the pressure increases
divergent shape
30
This divergent shape in subsonic inlet works like a venturi in that as the intake air spreads out, the velocity of the air____________
and the pressure ___________
decreases
increases
31
The added pressure in the divergent section in subsonic inlet contributes significantly to ___________________ once the aircraft reaches its design cruising.
engine efficiency
32
What is the main difference of supersonic and subsonic inlets
Below supersonic speeds, the intake must be able to recover pressure in the same manner as a
subsonic intake
but above supersonic speeds, the intake must be capable of reducing the velocity of airflow below sonic velocity by the formation of shockwaves.
33
The use of _____________intakes allow the correct control of intake shocks.
variable geometry
34
It may compromise spill doors to allow excess air to be spilled from the inlet without having its velocity changed.
variable geometry
35
the use of variable geometry may also compromise _____________to allow excess air to be spilled from the
inlet without having its velocity changed
spill doors
36
Some of the earliest
types of supersonic aircraft featured a ___________, called an _________, which was used
to form a shock wave
central shock cone
inlet cone
37
how convergent-divergent diffuser in supersonic inlet works?
it works because supersonic airflow will slow down as it enters a constricted area
38
Air flowing at subsonic speeds will accelerate through a constriction. Subsonic airflow through a venturi accelerated toward the ___________. At these speeds, the air will maintain a constant ____________, so a _____________ is set up which causes the air to accelerate through the constriction
throat
density
pressure wave
39
At supersonic speed, the ______________can’t move out ahead of the air and cause it to accelerate. Therefore, the air becomes more dense and slows down.
pressure waves
40
The objective of the convergent-divergent
diffuser is to slow the airflow to ___________ just
before the throat of the diffuser.
mach 1.0
41
Generally, the convergent-divergent diffuser is only suitable for short bursts of supersonic flight, at less than ____________
mach 2.0
42
For sustained speeds at or above Mach 2.0, the convergent-divergent diffuser was modified to use _____________ to control the airflow into the engine.
variable ramps
43
The________________________ automatically varies with aircraft speed and positions the shock wave to reduce the air velocity at the inlet, and also maintain maximum pressure recovery within the inlet duct.
angle of the variable throat area intake
44
why do we have to angle the variable throat area intake ?
1. it automatically varies with aircraft speed.
2. it positions the shock wave to reduce the air velocity at the inlet
3. maintain maximum pressure recovery within the inlet duct
45
what are the different type of supersonic diffusers
1. inlet cone
2. convergent-divergent diffuser
3.center body design
46
this design of supersonic diffuser has a sharp center body
center body design
47
center body design has a sharp center body sometimes called ____________
spike
48
this strikes
the airflow producing an oblique shock wave.
spike
49
A __________________ then slows the airflow
further before it reaches the compressor. The
position of the spike, in relation to its distance
ahead of the inlet, must vary with the speed of
the aircraft.
divergent chamber
50
The position of the spike, in relation to its distance ahead of the inlet, must vary with the speed of the aircraft. This is accomplished by making the _______________________ of the inlet. It will be extended as the aircraft flies faster and retracted as it slows down
center body position controllable fore and aft
51
what happens to the spike as the aircraft flies faster?
the spike will be extended
52
what happens to the spike as the aircraft flies slows down?
spike retracts
53
They have a convergent profile that
is designed specifically for obtaining very high
aerodynamic efficiency when stationary or in
slow flight.
Bellmouth Inlets
54
They are typically used on helicopters
bellmouth inlets
55
A typical __________ is short in
length and has rounded shoulders offering very little air resistance.
bellmouth inlet
56
It is the component that forces air
into the engine
Compressor section
57
Its main objective is to supply
compressed air for combustion in the combustion chamber
combustion chamber
58
This is the outlet pressure divided by the inlet pressure.
Compressor pressure ratio
59
The amount of air passing through the engine is dependent upon three factors:
1. The compressor speed (rpm);
2. The forward speed of the aircraft;
3. The density of the ambient
(surrounding) air
60
To be effective, a modern compressor must increase the intake air pressure __to __ times
above the ambient air pressure and move the air at a velocity of ___ to ___ _____.
20
30
400 ft/s
500 ft/s
61
How to increase the efficiency of the gas turbine engine?
the air being fed into it must be
compressed, before it has fuel added to it, and it
is burnt in the combustion chambers, and it is
subsequently expanded in the turbines
62
What are the functions of the compressor section.
1. it supplies air in
sufficient quantity to satisfy the
requirements of the combustion
burners
2. It supplies bleed air or
customer bleed air for various purposes in the engine and aircraft.
63
It is taken from any of the various
pressure stages of the compressor.
Bleed air
64
Bleeding air from the compressor does cause a small but noticeable drop in ______________.
engine power
65
Sometimes power loss can be detected by observing the
______________________.
Engine Pressure Ratio (EPR) indicator
66
Bleed air is utilized in a wide variety of ways. Some of the current applications of bleed air are:
1. Cabin pressurization, heating, and cooling;
2. De-icing and anti-icing equipment; and
3. Pneumatic starting of engines
67
Types of Compressor
1. Centrifugal Flow Compressor
2. Axial Compressor
3. Multi-spool compressor
68
Centrifugal Flow compressor is also known as
radial outflow compressor
69
This type of compressor is one of the earliest
compressor designs and is still used today in
some smaller engines and auxiliary power units
(APUs).
Centrifugal Flow Compressor
70
Centrifugal compressors consist of:
1.Impeller (also called rotor);
2.Diffuser; and
3. Manifold
71
Centrifugal compressors have a high pressure
rise per stage that can be around ____
8:1
72
Generally centrifugal compressors are limited to ____ stages due to efficiency concerns
two
73
The ____________consists of a forged disk with integral blades fastened by a splined coupling to a common power shaft.
impeller (rotor)
74
Its function
is to take air in and accelerate it outward by
centrifugal force
Centrifugal Compressors
75
Compressors having only one impeller are
referred to as_____________--while
compressors having two impellers are referred
to as ________________
single-stage compressors
double-stage compressors
76
When two impellers are mounted back-to-back, a __________________ or ________________ impeller is
created.
double-sided impeller
double-entry impeller
77
A ___________________allows a
higher mass airflow than that of a similar sized
single-stage, single-sided impeller. Therefore, engines “with _________________-typically have a smaller overall diameter.”
single-stage, double-sided impeller
double-sided impellers
78
Explain the Process of compression in a centrifugal flow compressor.
79
what happen when air passed through the flame area at high velocity?
it could extinguish the the flame
80
The ___________---
acts as an divergent duct where the air spreads
out, slows down, and increases in static
pressure
diffuser
81
It distributes the air in a smooth flow to the combustion section
compressor manifold
82
The ________________ diverts the flow of air from the diffuser, which is an integral part of the manifold, into the combustion chambers.
compressor manifold
83
The manifold has ___________for each chamber so that the air is evenly divided
one outlet port
84
where is the turbine assembly atttached?
compressor shaft
85
It converts the pressure, velocity, and heat of the gasses passing through the turbine into mechanical energy.
turbine assembly.
86
The mechanical energy produced by turbine energy is used to drive the ____________ of the compressor round the at high speed.
impeller
87
Air is introduced continuously into the eye or center of the impeller, by _____________, and centrifugal force causes the air to flow
causing the air to flow outwards, across the impeller, towards the tip.
rotating guide vanes
88
Because of the divergence between the impeller blades, the pressure of the air ___________ as it flows outwards between them, and because the turbine is adding mechanical energy into the
equation, the velocity of the air also _____________.
increases
increases
89
The_______________ is a
system of stationary divergent ducts which are
designed to convert the kinetic energy of the
airstream into potential energy.
diffuser section
90
The compression ratio of a single stage
centrifugal compressor could be in the region of _______-.
4:1
91
why engine compression ratios higher than 12:1 are not considered possible using a centrifugal compressor.
Excessive centrifugal loading prohibits efficient operation of a third stage
92
In an _____________, the airflow is along
the horizontal axis of the compressor.
axial flow compressor
93
an axial flow compressor has two main elements:
rotor and a stator
94
The task of this compressor is
to raise air pressure rather than air velocity
axial compressor
95
The ________________ converts the velocity
of the airstream, its kinetic energy, into potential energy, or pressure
axial flow compressor
96
The rotor consists of rows of blades fixed on a
_____________.
rotating spindle
97
The angle and airfoil contour of
the blades forces air _________ in the same
manner as a propeller
rearward
98
The rotor blades are usually made of
____________l with the latter stages
being made of ____________.
stainless steel
titanium
99
The design of blade attachment to the
rotor disk rims varies, but they are
commonly fitted into the disk by either
_____________________________, _____________-.
bulb-type or fir-tree methods
dovetail
100
Some long fan blades have a_____________
that helps support the blades, making them more resistant to the bending forces created by the airstream
mid-span shroud
101
The ________________, however, do block some
of the airflow and create additional aerodynamic drag that reduces fan efficiency
shrouds
102
This ___________t compensates for the blade velocity variation caused by its radius
twist
103
The _______________ are arranged in fixed rows between the rows of rotor blades and act as diffusers at each stage, decreasing air velocity and raising pressure.
stator vanes
104
The stator vanes are fastened to the _________________.
compressor out casing
105
The spaces between the rotor blades
and stator vanes form divergent passage.
divergent passage
106
The set of stator vanes immediately in front of
the first stage rotor blades are called ___________
inlet guide vanes
107
in a axial compressor, These vanes direct the airflow into the first stage rotor blades at the best angle while imparting a swirling motion in the direction of engine rotation.
inlet guide vanes
108
This action improved the
aerodynamics of the compressor by reducing the drag on the first stage rotor blades.
the imparted swirling motion by inlet guide vanes
109
Stator vanes are normally constructed
out of _______ or _____because those
metals have high fatigue strength.
steel or nickel
110
Stator vanes are often shrouded at their
tips to minimize _______________.
vibration tendencies
111
Some axial compressors with high
compressor pressure ratios utilize
________________ plus ___________________.
variable inlet guide vanes
several stages of variable stator vanes
112
These _________________ and
stators automatically reposition
themselves to maintain proper airflow
through the engine under varying
operating conditions.
variable inlet guide vanes
113
The last set of vanes the axial compressor air passes
through is the _____________-.
outlet vane assembly
114
These vanes
straighten the airflow and eliminate any swirling
motion of turbulence
outlet vane assembly
115
A number of disks are fastened together to form an ______________, which is driven by the ________________.
integral rotor drum
turbine
116
The number of stages is determined by the ___________and __________- required
amount of air
total pressure rise
117
A single stage in an axial flow compressor is
capable of producing a compressor pressure
ratio of only ____________-.
1.25:1
118
what kind of energy is velocity
kinetic
119
what kind of energy is pressure
potential
120
In the rotor blades, which are turned
continuously at high speed by the____________-,
mechanical energy is added and converted into
both kinetic (velocity) energy and potential
(pressure) energy.
turbine
121
Within the stator vanes, the
air pressure is increased by the conversion of the ___________energy into _________ energy.
kinetic
potential
122
So in order to achieve compression ratios demanded by more powerful engines, _______________________________________________________________________, which is driven by its own turbine
many rotor stages may be fitted on one shaft
123
A number of compressor rotor stages on a single shaft, which is driven by a turbine, is termed a __________.
spool
124
The space between the rotor drum and the
compressor outer casing is called the ________________________
air annulus.
125
To maintain the axial velocity of the air
reasonably constant as it passes through the
compressor, _____________________________
the size of the air annulus must be reduced
126
The gradual convergence of the annulus is
achieved by ___________________________________________________________________________________
either tapering the compressor outer casing or the rotor drum, or in some cases, a combination of both is used.
127
There is a vectorial relationship between the
_________________________________ and _____________________________that gives us the angle of attack over the rotor blade, and determines the __________________- either side of the blade
axial velocity of the air flowing through the
compressor,
the rpm of the compressor,
pressure zones
128
The compression ratio of this compressor is
_____--, at _________-- engine rpm.
22:1
100%
129
Engine designers devised a way to overcome the limitations of a single-spool compressor by
______________________________________
splitting the compressor into two or three
sections.
130
What makes one shaft makes it increasingly difficult to retain the ability to operate the engine over a
reasonable rpm range.
having many compressors stages
131
When do Compressor blade angles are arranged to give peak performance around maximum rpm?
it is when the axial velocity of the airflow and rotational speed of the blade produces the optimum angle of attack of the airflow over the blade
132
When does compressor stall becomes ever present at lower engine speeds?
when there is reduction in the engine rpm causes the angle of attack to reduce from its optimum value
133
what do designer did To overcome the tendency of the compressor stalling at low rpm
Designers split the compressor, initially into two separate sections. The sections were called respectively the high pressure, or HP compressor, and the low pressure, or LP compressor
134
In later, more powerful engines, designers split
the compressor into three sections namely:
High pressure compressor
Low Pressure Compressor
Intermediate Compressor
135
Each compressor section in is driven through a __________by its own ________________
shaft
turbine
136
average rpm of high pressure compressor in a multi spool compressor
22000 rpm
137
average rpm of intermediate pressure compressor in a multi spool compressor
14000 rpm
138
average rpm of high pressure compressor in a multi spool compressor
4000 rpm
139
What is the relationship of the speed of rotation of the compressors and its pressure status
they are directly proportional
140
what happen to the speed of low pressure spool when the throttle is closed
low-pressure spool falls up more rapidly than
the intermediate pressure and high-pressure
spools, it can be arranged that the optimal shape of the vector diagram
141
When referring to the speed of rotation of a
spool, the low-pressure spool is called the __
N1
142
When referring to the speed of rotation of a
spool, the intermediate pressure spool is called __
N2
143
When referring to the speed of rotation of a
spool, and the high-pressure spool is called
N3
144
The _________ is supported in bearings, and is
coupled to the turbine shaft in a manner that will allow minor variations in alignment to be
catered for.
rotor shaft
145
The centrifugal load on the compressor dictated that the rotor blades are fixed to a _____, which itself is fitted around the rotor shaft
disk
146
in a multi-spool compressor, The most common type of rotor blade fixing
method where the root of the blade is shaped to form a ____________, and is secured to the disk by a___ or ____________ ____.
dovetail joint
pin
locking tab
147
why is compressor blades are quite loose until seated by centrifugal force during engine.
for thermal expansion
148
It has become difficult on smaller engines to
design a practical compressor blade fixing
method, and at the same time maintain
minimum rotor disk weight. One solution to the problem is to produce blades integral to the disk, this type of blade and disk combination is called a___________.
blisk
149
where do stator vanes fastened?
1. Either fixed into stator vanes retaining ring which are themselves fastened to the casting.
2. hey are fixed to the compressor casing directly as applied on shrouded vanes
150
The _______ prevents the stator vanes
vibrating.
shrouding
151
The vibration can be induced by the
__________________________________.
velocity of the airflow over the vanes
152
In a multi-spool casing, The compressor casing at its low-pressure end is constructed of _______________________.
aluminum alloy
153
In a multi-spool casing, the intermediate casing is manufactured from _____________.
steel alloys
154
In a multi-spool compressor, Around the high pressure section of the compressor, only ____________________________ are capable of withstanding high air temperatures
nickel based alloys
155
Rotor blades are normally made from ______________
nickel alloys
156
In a multi-spool compressor, Some of the low
pressure stages of the compressor, where the
temperature of the compressor is not too high,
may have their rotor blades manufactured from
_________
titanium
157
Early engines used ____________ in the
manufacture of stator vanes, but they did not
withstand foreign object ingestion damage at all well
aluminum alloys
158
__________________, which
have a high fatigue strength and are less easily
cracked or eroded by impact are now used in the
manufacture of stator vanes.
159
_________________ is occasionally used for the
manufacture of the vanes in early stages of the
compressor, but it is not suitable for the
production of the smaller vanes further into the
engine, where the high temperatures of
compression can adversely affect it
Titanium
160
Another problem in titanium which may occur involves _____________. It is where the rotor blades come into contact with the compressor casing. Sufficient heat from friction may then be generated to ignite the titanium. This would, at best, require expensive repairs, or at worst, cause an airworthiness hazard.
blade rub
161
The high bypass ratio engine’s fanbades, were, in early engines, manufactured from solid
titanium, because titanium combines the
properties of strength and lightness. A low
blade-weight is essential if the fan is to be able
to withstand the out of balance forces which
would occur if a fan blade failed.
162
Despite the enormous strength of titanium, the
fan blades had to have a ____________ incorporated
into their design
snubber
163
A _____________ is a support which prevents
aerodynamic instability.
snubber
164
The greatest advancement has been achieved by fabricating the blade from a _____________________. This method of manufacture gives the fan blade
added strength with less weight, enabling the
introduction of the wide chord fan blade. The
stability of the blade is ensured as a result of its
wider chord and therefore the snubber is no
longer necessary
honeycomb core sandwiched between two outer skins of titanium
165
The reduction in axial velocity can reach a point
where turbulent airflow and a phenomenon
called ____________may occur.
stall
166
_____________ is a partial breakdown of the airflow through the engine and is a progressive condition, which, if not checked, may produce an event called_________.
stall
surge
167
__________ is a total breakdown of airflow through
the engine, which can, in the worst case, cause
the airflow through the engine to
instantaneously reverse its direction of flow.
Surge
168
A ____________ occurs when the compressor
blades’ angle of attack exceed the critical angle
of attack.
compressor stall
169
_____________ typically occur when
the engine inlet air becomes turbulent
or disrupted when an aircraft flies in severe turbulence or performs abrupt
flight maneuvers.
Compressor stalls
169
_____________ produced by a
sudden engine acceleration,
accompanied by incompatible engine
rpm and airflow combinations.
Excessive fuel flow
170
______________ are severe stalls that can
significantly impair engine performance, cause
loss of power, and can damage the engine.
hung stall
170
To minimize the airflow problems which may
occur after the first rotor stage has been
negotiated, when the engine is operating at other than its optimum conditions, some engines are fitted with___________
variable stator vanes
171
____________ can be progressively
closed automatically, so that as the compressor
speed is reduced from optimum design value,
they maintain the airflow onto the following
blades at an acceptable angle of attack
Variable stator vanes
172
If a ________________ is fitted to the
compressor casing at a position adjacent to the
intermediate stages of the compressor, it can be opened at low rpm and during engine
acceleration, to allow some of the excess
volume of air to escape.
compressor bleed valve
