Chapter 1.2: Intro to Turbofan engine

Question 1

what is bypass air?

Answer 1

air that goes around core engine and produce 80% of thrust

will not go through core stages

Question 2

what is bypass air used for?

Answer 2

cooling engine components & producing thrust

Question 3

what is primary air?

Answer 3

core air that goes into internal stage

Question 4

how many percent of thrust is produced by primary air?

Answer 4

20%

Question 5

how does core air help to produce thrust?

Answer 5

core air turns turbine > turns compressor and fan blades > fan blade turns means bypass air flow through > majority of thrust produced

Question 6

what is fan blade responsible for?

Answer 6

producing majority of thrust from fan air

Question 7

what is compressor responsible for?

Answer 7

compressing core air so internal energy of gas is increased

Question 8

what does LPT energy drive?

Answer 8

LPC & fan blade

Question 9

what is connected on the same shaft with LPT?

Answer 9

fan blade & LPC

Question 10

what does HPT do?

Answer 10

extracts energy from gas coming out of combustor

Question 11

what does LPT do?

Answer 11

extracts energy from gas that comes out of HPT

Question 12

what does HPT’s energy drive?

Answer 12

HPC

Question 13

what are the triple spools naming configuration?

Answer 13

low pressure - N1
intermediate pressure - N2
high pressure - N3

if no IP:
LP - N1
HP - N2

Question 14

what is HPC responsible for?

Answer 14

compressing core air from LPC before going into combustor

Question 15

what is the best mach number for turbofan?

Answer 15

M0.85

Question 16

reason for split spool

Answer 16

first blade is biggest and slowest, split to not drag down blades that are behind and smaller, allowing them to run faster

Question 17

rank compressors in terms of rpm

Answer 17

HPC > IPC > LPC

Question 18

why is triple spool engine not good?

Answer 18

more bearings needed > reliability decreases & maintenance needed higher

Question 19

which component is weakest in engine and why?

Answer 19

bearings

high stress & heat, if 1 ball bearing break, will cause vibration and domino effect on other bearings)

Question 20

bypass ratio formula

Answer 20

mass of bypass airflow / mass of primary airflow

Question 21

what is engine pressure ratio?

Answer 21

total pressure ratio across engine

Question 22

what is the range of EPR?

Answer 22

1 < EPR < 2