Analysis of Turbofan Engine

P M V Subbarao

Professor

Mechanical Engineering Department

How to decide Cold Vs Hot ???

Inlet

Ideal Turbofan Cycle

totalm

1 2 3

4 5 6 7h

7cTotal thrust is generated by both cold and hot jets..

corem

fanm

fanm

totalmcorem corem

Analysis of fan

0,003 prp fanp 0,003 TT fanp

Inlet

2 3

airmfanm

corem

Design Parameter : Stagnation pressure ratio

fanppcorefan TcmW ,00 11

Analysis of Fan

Analysis of Compressor

0,0,004 prrp comppfanp 0,0,004 TT comppfanp

comppfanppcorecompressor TcmW ,0,00 1

Inlet

Design Parameter : Stagnation pressure ratio

3

airmfanm

corem

4

Inlet

airmfanm

corem

4 5

comppfanpccpcorefuel fTcmVHm ,0,0,00 1..

cc

p

comppfanpcc

TcVH

f

,00

,0,0,0

..

Combined Gas Dynamic & Thermodynamic SSSF model for Turbine Inlet

airmfanm

corem

5 6

turbpccpcoreturbine TcfmW ,00,0 11

cc

fanpcomppfanpturbp f ,0

,0,0,0,0 1

1111

0,0,006 TT turbpcc

1,0,0

turbpturbpr

0,0,0,006 prrrp turbpcomppfanp

Vigor of Hot Jet

0,0,006 TT turbpcc

0,0,0,006 prrrp turbpcomppfanp

Combined Gas Dynamic & Thermodynamic SSSF model for Hot Nozzle

hcorecore hfmhfm 0706 11

hTT 0706

06277 2

11 TMT hh

0,0

,0,0,0,006 1

1111 T

fT

cc

fanpcomppfanpcc

27

0,0

,0,0,0,0

7

21

1

1

1111

h

cc

fanpcomppfanpcc

h

M

Tf

T

Available life at the inlet to the nozzle will decide the magnitude of T7h.

0,0,0,00607 prrrpp turbpcomppfanph

0,0,0,0

1272

11 prrrMp turbpcomppfanph

11

21

0,0,0,07

p

prrrM turbpcomppfanph

27

0,0,0

,0,0,0

7

21

1

1

1111

h

cccc

fanpcomppfanp

h

M

Tf

T

1

0,0,0,0

0,0,0

,0,0,0

7

1

1111

pp

rrr

Tf

T

turbpcomppfanp

cccc

fanpcomppfanp

h

11

2 0,0,0,07777 T

TRTRTMV turbpcomppfanphhhh

1

1

2 0,0,0,0

,0,0

,07 T

TRTV turbpcomppfanp

comppfanp

cch

comppfanp

cch

TT

,0,0

,07

TT

TT

turbpcomppfanp

turbpcch

0,0,0,0

0,0,07

20

2

11 acM

T

T

1

1

2 0,0,0,0

,0,0

,07 T

TcV turbpcomppfanp

comppfanp

cch

12

11

1

2 2,0,0,0

,0,0

,0jet acturbpcomppfanp

comppfanp

cchot McV

Combined Gas Dynamic & Thermodynamic SSSF model for Cold Nozzle

ccorecore hmhm 0703

0,0277 2

11 TMT fanpcc

TT c7

1

0,003

1

03037

pr

pT

p

pTT

fanpc

1

0,00,07

pr

pTT

fanpfanpc

1

1

2 0,0777 T

TRTRTMV fanpccc

0,0277 2

11 TMT fanpcc

T

TM fanpc

0,0

272

11

11

2 0,0

27 T

TM fanpc

12

11

1

2 2,077 acfanpcccoldjet McRTMV

12

11

1

2 2,0,0,0

,0,0

,0acturbpcomppfanp

comppfanp

cchotjet McV

Generation of Thrust : The Capacity

achotjetcoreaccoldjetcore

corestreamTfanstreamTtotalT

VVfmVVm

FFF

1

,,,

Propulsive Power or Thrust Power:actotalTp VFP ,

Specific Thrust based on core flow S

core

totalTcore m

FS

,

Specific Thrust based on total flow S

1,

core

totalTtotal m

FS

Thrust Ratio

Ratio of specific thrust of core stream to specific thrust of fan stream.

fan

core

fan

fan

core

core

F

F

mF

mF

FR

Thrust Specific Fuel Consumption TSFC

totalT

fuel

F

mTSFC

,

accoldjetachotjet

jetcoldcoreachotjetcore

fuel

VVVVf

f

VVmVVfm

mTSFC

1

1

Aviation Appreciation

Propulsion Efficiency

Jet theofPower Kinetic Available

PowerThrustpropulsion

2222

,

12 accoldjetachotjetcore

actotalTpropulsion

VVVVfm

VF

21

2221

2

VVVVf

VS

coldjetachotjet

accorepropulsion

Performance Analysis of Turbofan

• Operational Parameters : Flight Mach number & Ambient conditions.

• Design Variables : Fan Pressure Ratio, Bypass Ratio, Compressor Pressure Ratio, Combustion Chamber Temperature Ratio.

• Fan Effects :

• Fan Pressure Ratio

• Bypass Ratio.

• Fan Stream Thrust Vs Total Thrust.

ac

total

V

S

ac

core

V

S

TSF

C

Utility of of Fan Bypass Ratio

r0,p,fan=2.5 r0,p,comp=15 T0max=1200K Mac =0.75

Fan Effects …. : Fan Pressure Ratio: Mac = 0.75

r0,p,comp=15.0T0max=1200K

Effect of Flight Mach Number : CompactnessS

peci

fic

Thr

ust k

N.s

/kg

Mach Number

Effect of Flight Mach Number : Fuel Economy

TS

FC

Mach Number

Effect of Flight Mach Number : Propulsion Efficiency

Mach Number