INFLUENCE OF AXIAL COMPRESSOR FLOW PASSAGE GEOMETRY

CHANGES ON GAS TURBINE ENGINE WORK PARAMETERS

Pawe Wirkowski
The Polish Naval Academy
ul. midowicza 69, 81-103 Gdynia, Poland tel.:
+48 58 6262756, fax: +48 58 6262963 e-mail:
pawir@o2.pl, p.wirkowski@amw.gdynia.pl
Abstract
The paper deals with the problem of influence of changes variable stator vanes axial compressor settings of
gas turbine engine on work parameters of compressor and engine. Incorrect operation of change setting system
of variable vanes could make unstable work of compressor and engine. This paper presents theoretical analysis
of situation described above and results of own research done on real engine. On the base of results of
experiment there were determined mathematical equations determining relationships of changes of particular
engine work parameters in function of variable inlet guide stator vanes setting angle. There are presented results
of the solution of mathematical equations, which describe the changes of engine work parameters values too.

Keywords: gas turbine, axial compressor, variable stator vanes, modelling

Parameters, abbreviations and subscripts

1
KW
1 , 2
c1a
c1u, c2u
CO
HPC
HPT
S
i
LPC
LPT
K
m

1
pfuel
Pnom
PT

- air stream outlet angle with stator vanes,

- setting angle of variable stator vanes,
- air stream inlet and outlet angles in rotor vanes,
- axial component of air stream absolute speed on rotor blades inlet,
- circumferential components of air stream absolute velocity on the inlet and outlet rotor blades,
- combustor,
- high pressure compressor,
- high pressure turbine,
- compressor efficiency,
- air stream inlet angle on rotor blades,
- low pressure compressor,
- low pressure turbine,
- variable stator vane,
- air mass flow,
- compresssor rotor speed,
- angular velocity,
- fuel pressure,
- nominal engine power,
- power turbine,

S
u

- compression ratio,
- circumferential speed,

w1, w2 - air stream relative speed on inlet and outlet rotor blades,
VIGV - variable inlet guide vanes,
cu, wu - air stream whirl in the rotor,
VIGV - variable inlet guide vanes,
z
- number of inlet guide stator vanes,

1. Introduction and purpose of research

When in the compressor construction is assembled system of setting change of variable stator
vanes its task is to make optimal cooperation engine units during the permanent improvement of
compressor characteristic. Perturbations in the operation of this system could cause changes in
work of compressor and engine similarly as in the case of changes caused by changes of rotational
speed or polluted interblades ducts of compressor.
Compressor stage unitary work on radius is defined on the base of equation of angular
momentum and it has form
lst = r (c2u c1u) = ucu = uwu
where:
angular velocity, u tangential velocity, r rotor radius,
c1u, c2u circumferential components of air stream absolute velocity on the inlet and outlet
rotor blades on radius r,
cu, wu air stream whirl in the rotor.
That work is constant on whole depth of rotor blade. The sum of works is the unitary work of
stage [2]. Involved change of variable stator vanes angle setting at a constant level rotational
velocity (constant u) caused change of air stream inlet angle in rotor vane 1 (Fig. 1). It caused
change of axial component of air stream absolute velocity on inlet c1a what is equivalent with
the change of air mass flow m and change of air stream whirl wu in rotor. It influences on
efficiency and work of stage.
The purpose of investigations, which was carried out on real engine was determination of
influence of incorrect operation of axial compressor inlet guide variable stator vanes control
system of gas turbine engine on compressor and engine work parameters.
Compressor characteristic is a relationship between compression ratio S, compressor
efficiency S and air flow mass m and compressor rotational velocity n. It makes possible to
determine the best condition of compressor and another engine units mating. The characteristic is
used to select optimal conditions of air flow regulation and assessment of operational factors on
compressor parameters.
Therefore compressor should be so controlled in operational range of rotational velocity that
the compressor and engine mating line has a stock of stable work. The main rule of compressor
control during the change of their rotational velocity or flow intensity is to keep up the stream inlet
angles i value near zero. One of the most popular ways of axial compressor control is changing
their flow duct geometry by application of inlet guide stator vanes or variable stator vanes of
several first compressor stages [2].
This solution makes it possible to change of air stream inlet angle on rotor blades of
compressor stages by change of stator vanes setting angles during the change of compressor
rotational velocity. Fig. 1 illustrates the rule of regulation of variable stator vanes.
For average values of operational range of compressor rotor speed is situation in Fig. 1b
speed values and directions with subscript number 1. In this situation is intermediate angle setting
of stator vanes. Air stream inlet angle on rotor blades do not cause disturbance of stream flow by
interblades ducts. For lower values of compressor rotor speed and in consequence lower values of
absolute axial component velocity c1a, it is necessary to reduce the stream outlet angle

of variable stator vanes 1 (Fig. 1a). The angle reduction range should allow keeping the same
value of stream inlet angle on rotor blades. Analogical situation takes place during the work of
compressor with higher rotational speed. For higher rotational speed absolute axial component
speed c1a increases. In this situation for keeping stable work of compressor and in consequence
constant value of stream inlet angle on rotor blades, it is necessary to increase the stream outlet
angle of variable stator vanes Fig. 1c. Application in gas turbine engine construction of control
system of flow ducts geometry has a bearing on a run of unstable processes.
a)

b)

c)

d)

w1

1
c1a

wu
a1

a1

i=0

w1

w1

c1a

w1
c1a

c1a

Fig. 1. Essence of control of

compressors
axial stage by
changing the
setting angle of
stator vanes ring
at changeable air
flow velocity; a)
decreased axial
velocity, b)
analytical axial
velocity,
c) increased axial velocity, d)
schema of flow round
of axial compressor
rotor blades during
constant rotor speed
and constant air
stream inlet angles; k
variable stator vanes
ring, w rotor vanes
ring

2. Object of research
The object of research is type
DR 77 marine gas turbine engine,

2
w

which is a
part
of
power
transmissio
n system of
a warship.
It is threeshaft engine
with canring-type
combustor
chamber
and
reversible
power
turbine
(Fig. 2).

w2

INLET

pfuel

DUCT

FUEL

OUTLET
DUCT

CO
AIR
L
P
C

L
P
T
HPC

EXHAUST
GASES

PT

HPT
ELECTRIC
STARTER
GAS GENERATOR

POWER
TURBINE

Fig. 2. Block diagram of DR77 gas turbine engine

PROPULTION
LINE

In compressor construction configuration of this engine there are used inlet guide stator vanes
which make possibilities to change the setting angle incidance (change of compressor flow duct
geometry) in dependance on engine load. This process is operated by control system which
working medium is compressed air received from last stage of high pressure compressor. On Fig. 3
is presented block diagram of flow control signal of variable stator vanes system.
CLEANING
AND COOLING
BLOCK

CO
HPC

BLEED

VIGV

CONTROL
ACTUATOR

MOVING RING

p0, T0, 0
LPC

K K K
1
2

K
z

Fig. 3. Block diagram of stator vanes change setting mechanism

Compressed air from the last stage of high pressure compressor is supplied to working space of
control actuator by cleaning and cooling block. Compressed air exerts pressure on control actuator
elements. It causes moving of control piston which is connected with moving ring. This ring
moves on circumference of compressor body. Ring is connected with stator vanes by levers. When
the ring is moving stator vanes realize rotational motion changing the air stream outlet angle
1 (Fig. 1). In cleaning and cooling block are made holes. During research air stream was bleeded
by the holes and less air was supplied to the actuator. It caused change of setting angle KW of
variable stator vanes. In consequence of that change flow duct geometry was changed.
The experiment was carried out on an engine load 0,5P nom with taking into consideration
o
atmospheric conditions. For this load setting angle of variable vanes has value KW = - 4 . During
change engine load in the whole range from idle to full load setting angle KW of variable vanes
o
o
changes in range from -18 to +18 . During experiment a few parameters of engine work was
measured and registered. It was made for three different setting angle KW of variable vanes: A-KW
o

= -4 , B- KW = -11 , C- KW = -18 . Tab. 1 presents measured and registered parameters.

Tab. 1. Parameters of engine DR77 work measured during research
Parameter
nLPC
nHPC
nPT
p1
p21
p2
pp
T1
T42

Measurement range
0 20000
0 22000
0 10000
-0,04 0
0 - 0,6
0 - 1,6
0 - 10,0
-203 - 453
273 - 1273

Unit
[min-1]
[min-1]
[min-1]
[MPa]
[MPa]
[MPa]
[MPa]
[K]
[K]

Parameter name
low pressure rotor speed
high pressure rotor speed
power turbine rotor speed
subatmospheric pressure on compressor inlet
air pressure on low pressure compressor outlet
air pressure on high pressure compressor outlet
fuel pressure before injectors
air temperature on compressor inlet
exhaust gases temperature on inlet power turbine

3. Results of research
Change angle vanes setting from position A to position C caused the increase of air flow
resistance by stator vanes. In consequence of that subatmospheric pressure on the compressor inlet
p1 decreases. It causes pressure decrease in next parts of compressor and engine flow duct. In this
way reduced air density flowing by compressor, for stable quantity of stream fule supllied to
combustor, causes increase of compressors rotor speed. The most noticeable is increase of low

pressure compressor rotor speed caused by directly influence on this compressor incorrectly

setting variable stator vanes. Gasodynamical connection between the low pressure compressor and
the high pressure compressor absorbs disturbances work of low pressure compressor which are
transferred on high pressure compressor. Therefore range of change high pressure compressor
rotor speed is lower than low pressure compressor. In this experiment it is below 1% and it is in
measuring error of sensor range.
Change of subatmospheric pressure is above 5% undisturbed value of this parameter. Changes
of low and high pressure compressor outlet presure are adequately above 1,3% and above 2,4%
o
undisturbed value of angle setting KW = - 4 .
Changes of pressure and air mass flow intensity values accompanied disturbed work of
compressor, during constant fuel mass flow intensity in combustor, caused enrichment of fuel
mixture. As a result of that, temperature combustor outlet gases increases. In experiment was
confirmed the tendency changes of gases tempertaure values even though the range of those
changes is in measuring error of sensor range.
On the base of results of experiment there were determined the mathematical equations modelling
the changes of particular engine work parameters in the function of variable inlet guide stator
vanes setting angle KW :
2
n SNC = 0,7449KW + 2,602KW + 9234,5
(2)
2
n SWC = 0,0204KW - 1,1224KW + 12598
(3)
-6
2
-6
p1 = -10 KW - 10 KW + 0,0077
(4)
-16
p21 = 10 KW 2 + 0,0029KW + 2,9814
(5)
-16
p2 = 210 KW 2 + 0,0143KW + 8,1771
(6)
2

T42 = 0,0204KW + 0,1633KW + 526,33

(7)
Fig. 4 presents results of mathematical modelling of engine work parameters. Modelling was
cary out an state engine load what was equivalent unchangable fuel mass flow. In this case range
o
o
of change of variable inlet guide stator vanes setting angle KW was widen from -18 to +18 .
o
o
Researches in range KW from -4 to +18 were not possilble to realize on real engine. It is caused
by technical restrictions on the engine.

b)

9400

12600

SWC

9300

SNC

9200

9100

4 20

18 1614 1210

16

1816141210

420

-8

12550

86

high pressure compressor rotor speed

12650

9500

low pressure compressor rotor speed

[obr/min]

9600

[obr/min]

a)

101214o

angle setting of controllable vanes KW

10121416o1820

subatmospheric pressure on compressor inlet

c)

KW [ ]

angle setting of controllable vanes

air pressure on low pressure outlet compressor

d)

0,0008

0,304
0,302

0,00078
[MPa]

0,3
0,298

0,00074

0,296

21

[MPa _
]

0,00076

0,294
0,00072
0,292

angle setting of controllable vanes KW [o]

angle setting of controllable vanes KW [ ]

e)

10 12 14 16 18 20

-20-18-16 -14-12-10 -8-6-4-2024 68

40

-8
- 2 46 81 01 21 41 61 82 0

-2 0- - 16 - - 10

0,29
181412

0,0007

air pressure on high pressure outlet compressor

exhaust gas temperature on power turbine inlet

f)

0,85

809
807

p [MPa] _

805

42

803

T [K]

0,8

801
799
797

- 6- 4-20 2468 1012 1416 1820

-20

-4 -202 4681 0121 4161 820

-6

----- 201816141210-8
-

angle setting of controllable vanes KW [o]

-18-16-14-12-10-8

795

0,75

angle setting of controllable vanes KW [o]

Fig. 4. Change of values of engine work parameters in function of variable inlet guide stator vanes
setting angle gotten during mathematical simulation

4. Conclusions
o

Change of values of variable inlet guide stator vanes setting angle KW from -4 to +18 caused
the increase of stream outlet angle of variable stator guide vanes 1 (Fig. 1). It decreases air flow
drag on low pressure compressor inlet that caused decrease of subatmospheric pressure. During
keeping the constant engine load (constant fuel mass flow) absolute axial component velocity c1a
increases. It exerts an influence on air mass flow m increase. Simultaneously the absolute axial
component velocity c1a increase caused decrease of air stream whirl in rotor wu. In consequence
of that low pressure compressor rotor speed increases (Fig. 4a). In connection with decrease of
subatmospheric pressure the increase of air pressure on low pressure outlet compressor is caused
(Fig. 4d) . In spite of the slight decrease of high pressure compressor rotor speed the increase of air
pressure on low pressure outlet compressor involves the increases of air pressure on high pressure
outlet compressor (Fig. 4e). This slight decrease of high pressure compressor rotor speed caused
increase of gases flow drag in the next gas turbine engine units for the combustor. The effect of
above is a slight increase of exhaust gas temperature on power turbine inlet.
Multi-shaft construction of gas turbine engine reduces effects of incorrectly setting of variable
vanes. Therefore compressors of three-shaft gas turbine engine do not require variable stators
vanes as many stages as compressor of two-shaft engine with the same achievements.

Preliminary research confirms the necessity of inspection the correct operation of variable
stator vanes system control. It makes possibility of elimination this factor from group of factors
informing about technical state of engine which are identified during the diagnostic inspections.
References
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Naval Academy, Gdynia, 1991.
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Telecommunication Publishing House (WKi), Warszawa, 1982.
[3] Korczewski Z.: Wirkowski, P., Modelling gasodynamic processes within turbine engines
compressors equipped with variable geometry of flow duct, IV International
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Gas Turbines for the Canadian Navy, The American Society of Mechanical Engineers 345 E,
47 St., New York, N.Y.10017.
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gas turbine engine work, V International Scientifically-Technical Conference POLISH CIMAC
Explo-Diesel & Gas Turbine 07, Gdask-Stockholm-Tumba, Published by Gdask
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TH
with variable inlet stator vanes axial compressor, 12
International Conference
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