Turbofan - Terminology

Terminology

Afterburner
extra combustor immediately upstream of final nozzle (also called reheat)
Augmentor
afterburner on low-bypass turbofan engines.
Average stage loading
constant × (delta temperature)/
Bypass
airstream that completely bypasses the core compression system, combustor and turbine system
Bypass ratio
bypass airflow /core compression inlet airflow
Core
turbomachinery handling the airstream that passes through the combustor.
Core power
residual shaft power from ideal turbine expansion to ambient pressure after deducting core compression power
Core thermal efficiency
core power/power equivalent of fuel flow
Dry
afterburner (if fitted) not lit
EGT
Exhaust Gas Temperature
EPR
Engine Pressure Ratio
Fan
turbofan LP compressor
Fan pressure ratio
fan outlet total pressure/intake delivery total pressure
Flex temp
use of artificially high apparent air temperature to reduce engine wear
Gas generator
engine core
HPC
high pressure compressor
HP compressor
high pressure compressor
HPT
high pressure turbine
HP turbine
high pressure turbine
Intake ram drag
penalty associated with jet engines picking up air from the atmosphere (conventional rocket motors do not have this drag term, because the oxidiser travels with the vehicle)
IEPR
Integrated engine pressure ratio
IPC
intermediate pressure compressor
IP compressor
intermediate pressure compressor
IPT
intermediate pressure turbine
IP turbine
intermediate pressure turbine
LPC
low pressure compressor
LP compressor
low pressure compressor
LPT
low pressure turbine
LP turbine
low pressure turbine
Net thrust
nozzle total gross thrust - intake ram drag (excluding nacelle drag, etc., this is the basic thrust acting on the airframe)
Overall pressure ratio
combustor inlet total pressure/intake delivery total pressure
Overall thermal efficiency
thermal efficiency * propulsive efficiency
Propulsive efficiency
propulsive power/rate of production of propulsive kinetic energy (maximum propulsive efficiency occurs when jet velocity equals flight velocity, which implies zero net thrust!)
SFC
Specific fuel consumption
Specific fuel consumption
total fuel flow/net thrust (proportional to flight velocity/overall thermal efficiency)
Static pressure
normal meaning of pressure. Excludes any kinetic energy effects
Specific thrust
net thrust/intake airflow
Thermal efficiency
rate of production of propulsive kinetic energy/fuel power
Total fuel flow
combustor (plus any afterburner) fuel flow rate (e.g., lb/s or g/s)
Total pressure
static pressure plus kinetic energy term
Turbine rotor inlet temperature
gas absolute mean temperature at principal (e.g., HP) turbine rotor entry

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