mel341-29

8/20/2019 mel341-29

1/30

AXIAL FLOW COMPRESSORS

P M V Subbarao

Professor

Mechanical Engineering Depar!en

An Efficien Wa" o Inges Life in Large a!oun of Flui#s $$$

8/20/2019 mel341-29

2/30

An Option for High Specific Speed

• In aero applications, the specific speed is defined as:

( ) 43

hQ N s

∆

=

ω

and the flow coefficient as

2

22 Dr

Q

ω φ

=

4

3

∆=

ρ

ρ

p

mn

N s

8/20/2019 mel341-29

3/30

Sche!aic represenaion of an a%ial flo&

co!pressor

It is easy to design a turbine that will work…. It reuires a

considerable skill to design a co!pressor that will work…

8/20/2019 mel341-29

4/30

Anono' An())* Mriya

• The Antonov An-225 Mriya is a strategic airlift cargo aircraft,

designed by the Antonov Design Bureau in the 198s!

• Payload: 2", #g $"", lb% &&&

• Cruise speed: 8 #'(h!• Altitude) 11, ' $3*,1 ft%!

• Thrust +euired) 13" k"

• -o.er /lant) # $ %&'( )rogress *+- turbofans.

8/20/2019 mel341-29

5/30

he )rogress *+- / 0otare1 *+-2

• General characteristics

• Type: Three0s/ool high by/ass turbofan engine .ith a single0stage fan!

• an dia'eter) 2!33 ' $91!3 in%

• Dry weight: 4,1 #g $9,39 lb%

• Components

• Compressor: even0stage - co'/ressor, seven0stage a5ial 6-

co'/ressor • Combustors: Annular co'bustion syste'

• Turbine: ingle0stage 6- turbine, single0stage - turbine, four stage 7-‑

turbine

• Perormance

• !a"imum thrust: 229! #

• #verall pressure ratio: 2!"

• By/ass ratio) "!

• Turbine inlet temperature: 1,*:

• Thrust-to-weight ratio: A//ro5 "!)1

8/20/2019 mel341-29

6/30

8/20/2019 mel341-29

7/30

Stages of an A3ial+flow 4o!pressor

8/20/2019 mel341-29

8/30

Selection of )ressure 5atio per Stage

8/20/2019 mel341-29

9/30

he first step in a design of A3ial 6low

4o!pressor…..…..

he Aerofoil…

A 4ascade of Aerofoils…..

In1ention of high population ele!ent ……

8/20/2019 mel341-29

10/30

Aerofoil 7eo!etry

+: 8ero lift line

): leading edge

,: nose circle

-: ca!ber *: thickness

.: upper surface

/: trailing edge

0: !ain ca!ber line

1: lower surface

8/20/2019 mel341-29

11/30

7eo!etrical *escription of "A4A #9

8/20/2019 mel341-29

12/30

8/20/2019 mel341-29

13/30

"A4A #9 Series of Aerofoils

8/20/2019 mel341-29

14/30

4ascade of Aerofoils

8/20/2019 mel341-29

15/30

iscous flow through 4ascade

8/20/2019 mel341-29

16/30

4ascade 7eo!etry

; < stagger angle $ /ositive

for a co'/ressor cascade%

α=1 < blade inlet angleα=

1< blade outlet angle

8/20/2019 mel341-29

17/30

0ift ; *rag of a cascade

8/20/2019 mel341-29

18/30

Selection of Inlet flow angle

8/20/2019 mel341-29

19/30

4ycling of 'inetic

8/20/2019 mel341-29

20/30

Macro 2eo!eric Specificaion of An A%ial

Co!pressor

he geo!etry of a co!pressor can be

categorised into = !ain designs types,

A 4onstant Outer *ia!eter /4O*2, A 4onstant &ean *ia!eter /4&*2 or

A 4onstant Hub *ia!eter /4I*2,

8/20/2019 mel341-29

21/30

Specificaions of An A%ial

Co!pressor• here are se1eral different para!eters that can

specify a particular co!pressor.

• he first set of input para!eters are based on the

running conditions for the !achine.

• hese in1ol1e !ass flow, pressure ratio , rotational

speed and the nu!ber of stages.

• Stage degree of reaction : 6or controlling the

distribution of the load between the rotor and the

stator.

• If this is not of i!portance, the outlet flow angle

for the each stage !ust be set instead.

8/20/2019 mel341-29

22/30

a>?cp

p1T 1

p01T

01

p03 = p02 T 03 = T 02

a>>?cp

p2

a=>?cp

p3

s

T

( )w>w> r :r :@!.@) −==

3her!o#"na!ics of An A%ial flo&

Co!pressor Sage

8/20/2019 mel341-29

23/30

4ine!aics of An A%ial Flo&

Co!pressor Sage

Inlet elocity riangle

Outlet elocity riangle

8/20/2019 mel341-29

24/30

4ineics of An A%ial Flo&

Co!pressor Sage5ate of 4hange of &o!entu!:

( ) ( )f >>f ww> tanA:tanA:!::!6 −=−= ••



)ower 4onsu!ed by an Ideal

&o1ing (lade

( )f >>f tanA:tanA:B!) −= •

8/20/2019 mel341-29

25/30

..c!hh!) −=−= ••

+−+= •

p

>

a

p

>

a>>p

>c:.

>c:.c!

−+−=

•

p

>

a

p

>

a>>p

>c

:

>c

:..c!

−+−=

•

>

:

>

:hh!

>

a

>

a>>

8/20/2019 mel341-29

26/30

( )

−=−

>

:

>

:hh

>

r>

>

r>

( )

−=−

p

>

r>

p

>

r>

>c

:

>c

:..

Isentropic co!pression in 5otor (lade

−

=−

−

..ppp

>>

1γ

γ

*egree of 5eaction of A Stage, 5 : ( )

CC>

>

hh

hh5

−−

=

>

a

>

a>

>

r>

>

r

>

r>

>

r

::::

::5

−+−−

=

8/20/2019 mel341-29

27/30

Co!pressible Flo& Machines

• Owing to co!pressibility of gas in a co!pressor

• he degree of reaction for eual pressure rise in

stator and rotor will be greater than C.9.

• he stage total pressure rise will be higher in

order to get eual static pressure rise in stator

and rotor.

8/20/2019 mel341-29

28/30

Po&er inpu o he co!pressor 5

( ) ( ) ( )CC>pCC=pCC=act ..c!..c!hh!) −=−=−=

•••

4urrent )ractice:

21 f f f V V V ==

2211 tantantantan β α β α +=+= f V

U

heoretical )ower input to the co!pressor:

( ) ( )>f ww>th tanAtanAB:!::B!) −=−= ••

( )>f th tanDtanDB:!) −= •



8/20/2019 mel341-29

29/30

For an isenropic co!pressor5

( ) ( )>f CC=pth tanDtanDB:!..c!) −=−= ••

( ) ( ) CSpCC=pCC=pth E.c!..c!..c!)

•••

=−=−=

−

+=

1γ

γ

C

CS

C

isoC=,

.

E.

p

p

( )p

>f Cs

ctanDtanDB: E. −=

−

+=

1γ

γ

C

CSstage

C

actC=,

.

E.F

p

p

8/20/2019 mel341-29

30/30

( )

−

−

+=

1γ

γ

C

p

>f

stage

C

actC=,

.

c

tanDtanDB:

F

p

p

>a

>a>

>r>

>r

>r>

>r

::::

::

5 −+−−

=

>>

f

tanDtanAtanDtanA:

B +=+=

[ ]

>

>f r>

cosD

tanAtanDtanA::

−+=

mel341-29

Documents