MOD 1-2 Flashcards
Jet propulsion can be defined as
a method of propulsion produced when a mass of air is given acceleration
Sir Isaac Newton second law of motion
Force = mass x accelaration
Leonardo De vinchi create the first example of a reaction turbine and it called
chimnay jack
Sir Frank Little is consider the father of
of the jet engine, first flight Gloster E28
first German flight of a jet propeller
HE178-1100 Lbs Trust 400 m/h
Turbine Engine classifications
Turbo jet Turbo fan Turbo prop Turbo shaft
what is TSFC
Thrust Specific Fuel Consumption, how much fuel is consume to produce thrust
Turbo Jet characteristics
Low Thrust High TSFC at low altitudes and lower speeds long take off roll -disadvantage small frontal area lightest specific weight (weight for power produce) takes advantage of high ram pressure
Turbo Fan Characteristics
-increase thrust at speeds for short take off , but not falling off at higher speeds -weight lighter than TP heavier than TJ -medium TSFC -medium frontal area -reduce noise from turbo jet
Turbo prop characteristics
-high propulsive efficiency at low speeds -more complicated and heavier than TF and TJ -lowest TSFC -large frontal area -efficient reverse system (180 degree)
what is propulsion efficiency
is an indication of how much energy is being wasted or lost
turbo shaft
similar to turbo prop out to a transition or gearbox can not get a propulsive efficiency
3 Mayor sub classification of a gas turbine
axial centrifugal axial-centrifugal
why turbo shaft or turbo prop required gearbox
to reduce the speed of the blades or propeller not allowing get to the speed of sound
basic components of a turbine
air inlet, compressor, diffuser, combustors, turbine, tail pipe and jet nozzle
common engine identification
1-atmosphere
2-face compressor
3-discharge freom final compresor
4-combustion discharge
5-turbine section
6-turbine discharge
7- exhaust
what is creep strenght
the ability of a metal to resist slow deformation from strees of time, temp, load
engine cycle definition
VARIES BETWEEN MANUFACTURES
May be a start and RPM exceeding 80% N2
Maintenance run for leak check may not be counted as a cycle if RPM is kept below 80% N2
Some may only count a cycle if the wheels leave the
ground ( can do a full power run and not count a cycle
What is Yield Strength
the point when a metal takes on a permanent set due to application of a load
what is Rupture Strength
The point at which a metal will fail due to continual loading for long periods of time
Aluminum alloys carachteristics
Temperatures up to about 500
good strength to weight ratios
typical use-inlet ducts, centrifugal compressor components, accessory drive cases
Titanium alloys
temperatures up to about 1000 F
high strength, low density
•
typical use
-
centrifugal flow compressors, axial flow
compressor rotors and blades
ignition point is lower than melting point
does not dissipate heat well (low density)
Cold section parts
Steel alloys characteristics
temperatures up to about 1000 to1200 depending on the alloying elements
-low cost (relative to cost of other materials) ease of fabrication and machining
•typical use
compressor stators, engine structural members,compressor shafts, gears, cases
Nickel base alloy
- temperatures up to about 1200 to1800 F. depending on the alloying elements
- good high temperature strength
typical use–turbine wheels,turbine blades, shafts, combustion
liners
•Hot section parts
Cobalt base alloy
withstands high temperatures
- melting point–2700 F
- expensive
4 types cooling
Convection -heat disipades to the air
Inpingment-bleed air blown onto a hot part
Film-bleed air through holes
transpiration cooling -mesh
What is
N1
N2
Ng
Nf
N1 -Rotational RPM low compressor and turbine )
N2-rotation RPM high pressure compresor and turbine
Ng -RPM of the gas producer
Nf -RPM of free turbine
what is
ITT
TOT
TIT
Tt15
ITT-Inlet turbine temp
TOT- turbine outlet temp
TIT-turbine inlet temp
Tt15 -Turbine temp station 5
N1 and N2 is a measurment of what
rotational speed in % RPM
what is primary creep,secundary creep and tetiary creep
primary is a significant change that happens in a short period of time secundary is the slow deformation of the blade over a long period of time, tertery creep is a fast deterioration of the blade.
three prymary indications necessary for a gas turbine engine are
RPM
TEMPERATURE
TORQUE OR THRUST
Creep strenght is ussually referred to in terms of ?
time,temp,load
Brayton cycle is also known as ?
constant pressure cycle because the pressure in the combustion section remains the same
difference betwen potencial energy and kenetic energy
potencial energy relates to the mass, gravity and height and kenetic energy is in motion not in rest
difference between heat and temp
heat is the transfer of thermal energy and temp is the average kenetic energy
potencial energy can also reffered as ?
static pressure
kenetic energy canbe referred to as ?
dynamic pressure
according to bernoulis law, when fluid flows thruogh a divergent duct does the pressure increase or decrease
velocity decrease so pressure increase
according to bernoulis law, when fluid flows thruogh a convergent duct does the pressure increase or decrease
velocity increase so pressure decrease
in the Bryton cycle what section of the engine represents by point B to C
Combustion
in the Bryton cycle what section of the engine represents by point D to E
exhaust -turbine trust for propulsion (turbo jet and turbo fan)
in the Bryton cycle what section of the engine represents by point D to F
exhaust -turbine trust for propulsion (turbo prop and turbo shaft)
in the Bryton cycle what section of the engine represents by point C to D
Turbine
in the Bryton cycle what section of the engine represents by point F to G
represents the energy left in the gases after the last turbine (in a turbo prop).
in the Bryton cycle what section of the engine represents by point A to B
Compresor
on the engine map why does the pressure increase trought the convergent duct instead of decrease ?
because the divergent inside of the convergent duct
where is the highest total pressure in the engine
last part of the compressor stage
where is the lowest velocity ?
getting into the combustion section
why the specific heat of air under constant pressure, a higher BTU value that the specific heat air under constant volume
because the volume increase in constant pressure and requires more energy
performance limitation
RPM
turbine temp
torque or thrust
total energy= to?
potencial energy +kenetic energy
or
static pressure + velocity
total pressure = to?
static pressure +dynamic pressure
The area of a ____________decreases in
the direction of fluid is flowing
convergent duct nozzle
The area of a ______________increases in the direction of fluid is flowin
divergent duct (diffuser )
what is thermal efficency ?
A ratio of the engines energy output (thrust or
torque), to the fuel energy input
horsepower is equivalent to ?
1 HP = 33000 ft/min
1 HP = 550 ft/sec
amount of energy required to raise 1 # of air under constant volume ?
0.1715 BTU
amount of energy required to raise 1 # of air under constant pressure ?
0.24 BTU
specific heat formula what are the constants and what is Wa, delta T and |Cp ?
In the airflow through a convergent or divergent duct, the potential energy can also be referred to as __________.
static pressure
. In the airflow through a convergent or divergent duct, the kinetic energy can also be referred to as __________.
dynamic pressure
According to Bernoulli’s Principle, when a fluid flows through a convergent duct, does the total pressure increase, decrease or remain the same?
decrease
According to Bernoulli’s Principle, when a fluid flows through a divergent/diffusing duct, does the total pressure increase, decrease or remain the same?
increase
According to the General Gas Law, does “V” represent velocity or volume?
volume
According to the General Gas Law, if “V” is held constant and “P” increases, does “T” increase or decrease?
increase
