Chapter 3 Farokhi Flashcards
For a high bypass ratio turbofan.
What’s between station 0 and 2?
Inlet
For a high bypass ratio turbofan.
What’s between station 2.5 and 3 ?
HPC high pressure compressor
For a high bypass ratio turbofan.
What’s between station 3 and 4?
Combuster or burner
For a high bypass ratio turbofan.
What’s between station 4 and 4.5 ?
HPT high pressure turbine
For a high bypass ratio turbofan.
What’s between station 4.5 and 5 ?
LPT low pressure turbine
For a high bypass ratio turbofan.
What’s between station 2 and 2.5 ?
LPC low pressure compressor
For a turbojet with afterburner. What’s between station 0 and 2?
Inlet
For a turbojet with afterburner. What’s between station 2 and 2.5 ?
LPC low pressure compressor
For a turbojet with afterburner. What’s between station 2.5 and 3 ?
HPC high pressure compressor
For a turbojet with afterburner. What’s between station 3 and 4 ?
Combustor or burner
For a turbojet with afterburner. What’s between station 4 and 4.5 ?
HPT high pressure turbine
For a turbojet with afterburner. What’s between station 4.5 and 5 ?
LPT low pressure turbine
For a turbojet with afterburner. What’s between station 5 and 6 ?
Afterburner
For a turbojet with afterburner. What’s between station 7 and 9 ?
Nozzle
For a turbojet with afterburner. What’s on station 8 ?
Throat of the nozzle
A gas generator includes the following three for a jet engine.
Compressor 2->3
Combustion/burner 3->4
Turbine 4->5
Propulsive efficiency is defined as ?
n_p = F*V_o/DKEdot
At takeoff, the ______ is often ignored leading to a zero ram drag. F at take off is equal to F gross = (mA + mf)V9 + (p9-p0)A9
Airspeed Vo
When p9=p0 the nozzle is said to be ______ . Leading to the following equation for trust at takeoff:
Perfectly expanded nozzle
F=(ma+mf)V9
In a turbofan engine, the captured airflow is typically divided into a _____ flow where the combustion takes place and a _____ flow, where the so called bypass steam of air is compressed through a fan and later expelled through a fan exhaust nozzle. This type of arrangement (bypass) configuration leads to a ______ overall efficiency of the engine and a lower fuel consumption.
Core flow
Bypass flow
Higher efficiency
An example of an engine with more than a single stream is _____
With a more than one stream the Fnet uninstalled is the difference between____
Turbofan
Fnet = sum FgNozzles - sum DramInlets
The engine uninstalled trust is the difference between which two contributions ?
Nozzle contribution and inlet contribution
The nozzle contribution is called _______ . And is given by the formula Fg=(m+m)V9+ (P9-P0)A9
Gross trust
The inlet contribution is negative and its called _____ D = mV0
Ram drag
In turboprops and turboshaft engines thermal efficiency ignores and neglects the _______
Kinetic energy
The ability to convert the thermal energy inherent to a net kinetic energy gain is known as ____
Thermal efficiency
Ratio of net mechanical output over thermal input
DKEdot/Pthermal
All propulsiors, rockets, and air-breathers could be compared by using a unifying figure of merit, namely their specific impulses in seconds. Define specific impulse for both an air breather engine and rocket
Is = F/mf*g. Air breather
Is = F/mp*g. Rocket
Name a few figures of merit when designing an engine.
Engine thrust
Mass flow rate
Mechanical power/shaft output
Dry weight
In case of an air breathing engine, specific thrust is defined as ______
F/m ratio of thrust to air mass flow rate
Remember, we want to produce thrust with the least quantity of air mass flow rate
Define specific thrust in nondimesional form
F/m*a
a = ambient speed of sound
In the commercial world, perhaps the most important parameter of the engine is the _____
Where as for the military world are ______
Specific fuel consumption
Stealth, agility, maneuvered, survival
For an air breathing engine TSFC is defined as:
mf/F
Ratio of fuel flow rate per unit thrust produce
The reason why we can’t achieve 100% efficiency is because we can’t violate which law ?
2nd law thermodynamics
F installed = ? - ?
F uninstalled- D nacelle
The fraction of the net mechanical output(DKEdot) of the engine which is converted into thrust power(F*V) is called ______
Propulsive efficiency
n_p = F*V/DKEdot
The engine internal thrust is:
Mv9-mv1+p9A9-p1A1
True or false
True
The axial components of force felt by the inner walls of an air breathing engine are : Fxcompressor = Fx burner = Fx turbine = Fx nozzle =
I2-I3
I3-I4
I4-I5
I5-I9
Consider a rocket. In comparison to an air breathing engine the rocket system is missing the _____ .
Therefore, the inlet _____ contribution to thrust is also missing in the rocket thrust equation which is independent of the Vo flight speed.
Air intake
Inlet ram drag
Installation losses to the thrust include the following 3
Accurate measurements of these drags require ____ analysis and _____ testing.
Nacelle skin friction
Pressure drags caused by engine installation
Pylon drag
CFD and WTT
Additive drag minus the cowl lip force (suction force) is know as;
Spillage drag
In the study of propulsion we often concentrate on the engine internal performance I.e. _______ rather than the _______ performance
Uninstalled
Installed
If P9 < Po the nozzle is _____ which can happen in _____ jets only. These jets use large nozzles. These needs a ___ area ratio.
Over expanded
Supersonic
Large
If P9=Po the nozzle is _____ which is the case for all _____ jets and sometimes in sonic or supersonic jets. This configuration needs the ____ nozzle area ratio.
Perfectly expanded
Subsonic
Right
Is P9>Po the nozzle is _____ which can happen in _____ or _____ jets only.
Under expanded
Sonic
Supersonic
In deriving the axial force thrust of an engine we have to use the ____ principals.
Momentum
