1d performance of axial compressor

Axial compressor performance modelling

with a quasi-one-dimensional approach

N M White, A Tourlidakis and R L Elder

School of Mechanical Engineering, C ran eld University, Bedfordshire

Abstract: This paper describes a technique for the numerical modellin g of axial comp ressors using the

simplest form of representation—a mean-l ine one-dimensional method. Although this type of  ow analysis

is a gross simpli cation of a complex three-dimen sional system, which can now be mo delled more accurately

by many of today’s compu tational  uid dynamics (CFD) packages, it does offer th e advantages of simple

inpu t requirements and fast convergence times. These factors were major considerations when choosing a

program. A discussion of the results then follows, where fo ur very different compressors have been

modelled . Finally, the stability limit (or surge point) prediction methods are reviewed.

Results have shown that consistent agreement can be obtained with such a performance prediction model,

providing the loss and deviation correlations used are applicable to the b lade pro les. It was also apparent

that the two simplistic methods of surge prediction, which relied upon either stage or overall characteristic

gradien ts, gave better agreement than the more rigorous discrete stage-to-stage model. This was thought to

be a result of the continuous nature of the empirical rules utilized, which predict a smooth stage characteristic

and hence falsely delay the estimated instability point.

Keywords: axial compressor, peformance prediction, empirical mod els

NOTATION

axial chord

C matrix of steady  ow parame ters

C

f

coef cient of friction

C

p

speci c heat at constant pressure

C

v

blade diffusion factor

E

net

net stage work inp ut

F

net

net stage force

F

xs

axial blade force de cit (dissipation)

blade hei ght

s

V

total velocity or stage volume

V

a

axial velocity

V

w

whirl velocity

W

mass  owrate (kg/s)

Z matrix of geometric parameters

a

air angle (deg)

b

blade ang le

g

stagger ang le

d

deviation angle

d

y

blade cambe r angle

y

boun dary layer momentum thickness

n

Prandtl–Meyer expansion angle

r

density

s

c

s

1 blade inl et station

1 INTRODUCTION

The ability to pred ict the overall performance of modern

References [1] to [7] presen t a selection of quasi-one-

W

,

open literature a set of correlations that collectively give a

good overall performance prediction at design and off-

design conditions for a range of different compressors

program. The program will be subsequently coupled to a

previously develo ped at Cran eld by Gill and Elder [10]

and Escuret and Elder [11].

 nally incorporated (as subroutines) into an optimization

There are two basic requirements for the prediction of stage

each case, the actual method is similar and can be summar-

ized as follows:  rstly, a blade loading parameter is found

D

assuming that

remains constant at inlet and exit to the

bladerow and

. The corresponding pro le loss parameter,

are subseque ntly

o

.

o