Turbomachinery Basics

1

JongSik Ohojsturboojsturbo@@koreakorea.com.com

Turbomachinery BasicsCentrifugal Compressors

TURBOMACHINERY BASICSCENTRIFUGAL COMPRESSOR

JAN. 28, 2004

JONGSIK OH



WHAT ARE TURBOMACHINES ?

Rotating dynamic machines with energy transferdue to changes of angular momentum

Torque on fluid = Rate of change ofangular momentum

Angular momentum = Moment of momentum= Tangential force x Distance= Momentum flow x Distance= rCm θ&

2



EULER EQUATION

)CUC(Um TP Power

)rCrC(mT Torque

1122

1122

θθ

θθ

−=ω=

−=

&

&

2W

2C ω= 22 rU

ω= 11 rU

2Cθ

1Cθ

1mC

2mC

1C1W



RELAVANT UNIT

WsJ

kgJ

skg

sm

skgP Power

sm

kg

msmkg

kgm.N

kgJK

kg.KJ

gas) ideal(for TCh Enthalpy (Specific)

Watt:Unit )CUC(Um

TP PowerN.m :Unit

)rCrC(mT Torque

2

22

P

1122

1122

===

=

====×

=

−=ω=

−=

θθ

θθ

&

&

3



PREWHIRL OR PREROTATION

ω= 11 rU1Cθ

1C

1W

0C ,CC 11m1 == θ

1mC

1α



PART-LOAD CONTROL

4



SLIP FACTOR2W

ω= 22 rU

2mC

1W

ω= 11 rU

1r

2r

2Cθ

b2W

b2Cθ

b2β

2β

2α b2α

2Cb

2b

2

CC

θ

θ≡ζ



IMPELLER EXIT BLADE ANGLE

5



EFFICIENCY

efficiency polytropic the is where gases idealfor

1pp

1pp

gases idealfor 1

TT

1pp

gases idealfor TTTT

hhhh

Work alRe WorkIsentropic Efficiency Isentropic

P1

1

2

1

1

2

1

2

1

1

2

12

12'

12

12'

C

p

η

−

−

=

−

−

=

−−

=

−−

=

≡η

γη−γ

γ−γ

γ−γ

Independent of overall pressure ratios



ROTHALPY & TOTAL ENTHALPY

0hh const. enthalpy Total (a)

Region Vane Stationary

1OO2 =−=

const.

U21W

21h

U21hI

const. Rothalpy (b)CUCUhh

)C21h(h const. enthalpy Total (a)

Region Blade Rotating

sstreamlinealong machinesAdiabatic

22

2relO,

11221OO2

2O

=

−+=

−≡

=

−=−

+≡≠

θθ

6



ENERGY TRANSFER

0

1

2

3



SPECIFIC SPEED

Machine Operation Parameter

• Operation speed at which machine producesa unit head rise per unit flow rate

• Independent of machine SIZESIZE

U.S.)(for ft : H /s,ft : Q rpm, : N where

HNQ

DNgH

NDQ

N

3

4/3

2/1

4/3

22

2/1

3

S =

≡

7





8



(Balje) m : H /s,m : Q rad/s, : N where)gH(

NQN

3

4/3

2/1

S =



VANED DIFFUSER

9



VANED DIFFUSER



LSD (Low Solidity Diffuser)

10



AXIAL VANED DIFFUSER



VOLUTE/SCROLL

11



PERFORMANCE MAP



PERFORMANCE MAP

12



CORRECTED CONDITIONS

p(Pa) T(K), (kg/s),m N(rpm), where

101325p

15.288Tm

m

15.288TNN

1O

1O

CORRECTED

1OCORRECTED

&

&& ≡

≡

288.15N

TN

101325288.15m

pTm

0TN ,

pTm

,TT ,

ppf

0RTND ,

pDRTm

,TT ,

ppf

0)RT ,p ,m N, f(D,

AnalysislDimensiona

CORRECTED

O1

CORRECTED

1O

O1

O11O

O1

O1

O2

1O

2O

O11O2

O1

O1

O2

1O

2O

OO

=

=

=

=

=

&&

&

&

&



IMPELLER INCIDENCEchokesurge

• Note : Angles measured from meridional referencefor axial-flow cascade tests

• Note : When angles from tangential reference,negative incidence in choke

13



DIFFUSER INCIDENCE



SPLITTER BLADES

14



SPLITTER BLADES



IMPELLER BLADE GEOMETRY

15



SOME ANGLES



IMPELLER CFD

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