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111 1 11 1 111011 0)1 11 1 1111
AN EXPERIMENTAL INVESTIGATION ON THE AERODYNAMIC PERFORMANCE AND
FLOWFIELD STRUCTURE OF A FILM-COOLED TURBINE CASCADE
Chen Fu
Yang Hong
P. O. Box 458, Harbin Institute of Technology
Harbin 150001, China
Abstract
H,
Experiments have been performed to study the aerodynamic
cascade passage height
static pressure coefficient or the suction side leg of the
horseshoe vortex;
static pressure coefficient I
)
r_
)(
performance and internal flows in a linear turbine cascade with air
pc-p
c,
injection from various locations of the blade surface. Data were
obtained by using pneumatic probe, static pressure taps and surface
AH, difference of H, with/without injection
the pressure side leg of the horseshoe vortex
flow visualization techniques. The experimental results showed that
Hv
the suction side injection would affect the development of the
passage vortex significantly. The passage vortex was strengthened
incidence
LE,TE leading edge, trailing edge
Mach number
velocity ratios based on the local freestream values
PS,SS pressure side, suction side
S/D
relative spacing of injected holes
pitch
flow velocity
and pushed away from the injection surface, a triangular-shaped
region uncovered by the injected air always existed on the suction
surface due to the existence of the passage vortex. The passage vortex
was weakened with air injection from pressure surface, which would
cause a smaller amount of low momentum fluids to migrate into the
corner region between suction surface and end wall. Although the
scale and intensity of kidney-shaped vortices were different when air
was injected from various positions, these vortices might always exist
near the blade surface, mixing with mainflow in the flow passage and
with wakes at the cascade exit while they moved downstream. The
energy loss increased near the blade surface from which air was
injected due mainly to the mixing process between mainflow and
injected air, and to the formation of kidney-shaped vortices. In
AV, difference of secondary flow vectors with/without
injection
dimensionless distance from the hub normalized by the
Y/H
cascade passage height H
dimensionless distance normalized by the axial blade
VC,
chord C,„,
a
flow angle
mass
flow ratio. of injection air against mainflow
13
inlet geometrical angle
contrast to the pressure side injection, the changes of blade surface
pressure distribution were more sensitive to the amount of injected air
and the locations of injection holes for the suction side injection. In
Pip
Pb
outlet geometrical angle
stagger angle
the great majority of cases, the surface pressure decreases owing to
8
boundary layer thickness on cascade inlet end wall
the existence of low-pressure zone downstream of the injection holes
8
displacement thickness of cascade inlet end wall
boundary layer
momentum thickness of cascade inlet end wall boundary
layer
injecting angle
were more significant than the pressure increases caused by mainflow
stagnation upstream of the holes.
Nomenclature
axial chord length
C,„
chord length
injected hole diameter
energy loss coefficient;
4
C.Pif,. -lP/P; F ]/[1-(p/p;
Presented at the International Gas Turbine & Aeroengine Congress & Exhibition
Indianapolis, Indiana — June 7-June 10, 1999
Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 12/22/2014 Terms of Use: http://asme.org/terms
ans
difference of with/without injection
turing angle
cooling effectiveness on a cooled end wall and found interaction
between the injected coolant and the secondary flow. The results
showed that it was necessary to take the three-dimensional nature of
the end wall flow into account in the design of end wall film-cooling
configurations.
Subscripts
0
cascade inlet
1-9
number of measuring planes
The air injection can alter the flow field structure and lead to a
very complex three-dimensional flow structure due to the presence of
secondary flow in the cascade. A general overview of secondary flow
in turbine blade passage was given by Sieverding (1985). Wang et al.
(1995) and Friedrichs et al. (1996) also described the secondary flow
structures in the turbine cascade.
Superscripts
pitchwise mass-averaged value at each local span
•
overall mass-averaged value calculated at each measuring
plane
•
stagnation or total value
Introduction
Many studies have focused on the characteristics of flow field
structure on two-dimensional flat and curved plates with air injection.
Moussa et al. (1977) found from three-dimensional velocity
measurements in the near field of the jet exit that a pair of bound
vortices was formed in the downstream region due to the
reorientation of ring vortices emerging from the jet exit Crabb et al.
(1981) confirmed double vortex characteristic from turbulent
component data and showed that this was associated with the fluid
that escaped from the jet exit. Andreopouls and Rodi (1984) found
that the jet structure was strongly dependent on the velocity ratio. Lee
(1994) experimentally studied the inclined jets in the presence of
turbulent crossflow on a flat wall, and showed that the crossflow
fluids filled in the region between the wall and the jet trajectory.
Attempts to improve the performance of modem gas turbine
engines lead to higher and higher temperature at the turbine inlet of
the turbine section. The temperatures have reached such high levels
that the turbine blades need to be protected by efficient cooling. One
of the most effective cooling methods is film cooling by injection of
cooling fluids through rows of holes, and this method is now widely
used in practice. But even for one row of holes, a very complex flow
develops with a wide variety of influence parameters, such as the
blowing angles with respect to the surface and mainflow, the relative
spacing, the momentum ratio, the wall curvature and the state of the
incoming boundary layer. The injected air also leads to changes in the
aerodynamic performance and the flow field structure of the cascade,
there are flow losses associated with the mixing process. Under
unfavorable conditions, the gain achieved by the film cooling can be
used up by the flow losses, and hence the designer's goal is to use the
minimum amount of coolant necessary to insure adequate turbine life.
To this end, there has been considerable research to increase our
understanding of coolant film behavior and its interaction with the
mainflow flow.
Relatively less work has been done in the flow structure of a
turbine cascade. Dring et al. (1980) observed a large radial
displacement of coolant jet on the pressure surface in a low-speed
rotating facility. Abhari and Epstein (1994) investigated the influence
of three-dimensional and unsteady effects on the rotor film cooling
process in a transonic rotating turbine stage. Goldstein and Chen
(1985) showed that the film cooling jets were swept away from the
surface by the paqc.age vortex. Wilfen and Fotter (1994) studied the
mixing process in the near hole region with a row of holes on the
suction surface of a turbine cascade by using pneumatic probes and
flow visualization techniques. They concluded that the position of the
horseshoe vortex of each single jet was strongly dependent on the
blowing rate and influenced the aerodynamic mixing mechanisms.
In the last years, studies of the effects of film cooling upon the
aerodynamic performance were carried out by Ito et al. (1980),
Kollen and Koschel (1985), Goldstein et al. (1987), Manickam and
Murugesan (1989), Sieverding et al. (1994). Ligrani et al. (1991a,
1991b) described the influences of embedded longitudinal vortices on
film cooling from a single hole or a row of injection holes with
simple angle orientations in a turbulent boundary layer. One of the
most important conclusions from this studies was that magnitudes of
perturbations to injectant distribution were dependent upon the ratio
of vortex circulation to injection velocity times hole diameter, and the
ratio of vortex circulation to injection velocity times vortex core
diameter. According to Ligrani and Mitchell (1994), when air was
injected from film holes with compound angle configuration, the
injectant distribution were strongly affected by the longitudinal
embedded vortices, including their directions of rotation and their
spanwise positions with respect to film injection holes. Yamamoto
(1991) investigated the effects of air injection on the performance of
a linear turbine cascade with large turning angle and showed that
injection from the blade pressure or suction side generally decreased
the loss. Friedrichs (1996,1997) measured the distribution of film-
However, the investigations mentioned above have not been made
clear how the injected air behaves in the cascade passages and how it
causes the changes of aerodynamic parameters, as well as flow field
structure. The main intent of the present paper is that the internal
flows in the cascade passage are studied experimentally. Attention is
focused on the changes of three-dimensional flow field structure and
aerodynamic parameters caused by different locations of injection
holes and different mass flow rates. In the present paper, there are
nine rows of injection holes on the leading edge, suction surface and
pressure surface to simulate film cooling flows. Detailed cascade
tests consist of passage flow parameter traverses, blade and end wall
surface pressure distribution and flow visualization for the cases of
2
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TE
I
Mid span
r1/17.1r
ass&
i
id
s
s
1
_T
I .1.• ••• I
.....
S
S
"
"
;
;
......
,
•
•
,.11aarri
...
...
•-..;
midspan
'''
I.
;
I
1
1)
I
h- -
- )°14'
14
Ns.
—
End wall
A2
midspan
•
Fig. 7 Flow visualization results and the schematic drawing of flow field structure in the cascade passage
2,7-9 on the pressure surface, the distributions of the streamlines on
wall without air injection, N52 is located at about 10, 7.5 and 6.25
percent span with air injection. This shows that air injection on the
suction side of the blade may affect the development of the passage
the suction surface are not affected significantly, and it is the same for
the distributions of the streamlines on the pressure surface with air
injection from hole 3-6 on the suction surface. So only the flow
vortex, and at the same time, a triangular-shaped region uncovered by
the injected air always exists on the suction surface due to the
visualization results on the pressure surface with air injection from
hole 1,2,7-9 and the results on the suction surface for the cases of
hole 3-6 injection are presented in Fig.8.
existence of the passage vortex. For air injection from hole 1, 7-9 on
the pressure side, it is interesting to note that the distributions of the
ink drops on the blade surface are disordered downstream of the holes
As shown in Fig.8, the distributions of streamlines near the blade
up to the trailing edge, especially injecting from hole 1. The
surface are different compared to those without air injection. The
separation lines of the kidney-shaped vortices can not be seen clearly.
One explanation about these results may be that the air injected from
separation lines of the kidney-shaped vortices resulted from the
reoriented outgoing vortex rings issuing from the injection holes can
the holes on the pressure side attaches to the blade surface rapidly,
then the injected air/mainflow mixing process basically occurs in the
be seen downstream of the hole exit with air injection from hole 2, 46, existing on the blade surface up to the trailing edge. This means
boundary layer. To a certain extent, the occurrence of the mixing
that the original two-dimensional flow field near the blade surface
process means the existence of the kidney-shaped vortices, therefore
becomes three-dimensional due to air injection, the kidney-shaped
the kidney-shaped vortices may always exist downstream of the
vortices may always exist downstream of the injection holes and mix
out with the wake at the cascade exit under the present experimental
conditions. For the air injection from hole 4-6 on the suction side, the
injection holes with air injection from the pressure side. Compared
the visualization results of pressure side injection to that of suction
side injection, one may conclude that under the present experimental
separation line of the passage vortex, indicated by A l -Ns, on the
suction surface, is skewed toward the end wall. Compared to the
location of N s, lied at about 12.5 percent span apart from the end
conditions, the mixing process between the injected air and mainflow
occurs farther above boundary layer with suction side injection.
5
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1.0
1.0
0.8
0.8
0.6
0.6
Y/H
0.4
0.4
0.2
0.2
0.0
(a) Pressure-side view
(b) Suction-side view
0.00
0.06
ml
Fig 3 Schematic diagram of tested turbine blade
0.0
0.12 85.0
•
90.0
95.0
(1))
Le= -0 .8° , 5/H=0.094, S . /H=0.0098, C11=0.0065, 5. /er =1.5
Fig.6 Inlet Mach number and flow angle distribution
Flow near the blade surfaces and the cascade end wall is studied
using ink spread on contact paper attached the end wall and the blade
surfaces. During exposure to the tunnel flow, the streamlines are
traced on the paper. The flow visualizations are taken for the cases of
with/without air injection. Because the flow around a straight blade is
essentially symmetric, only the results on the one-half of the blade
surfaces and the lower end wall are presented.
Results and Discussion
Plane
2
3
4
20.0
Z, mm -38.0 -12.0 5.0
Z./C
-0.516 -0.163 0.068 0171
Flow Visualization Fig.7 shows the flow visualization results
and the schematic drawing of flow field structure in the present
cascade passage without air injection. A separation line, indicated by
A 1 -A2, is presented in the boundary layer, the attachment line, a 1 -a2,
extends from the incoming flow to the stagnation point and intersects
the separation line at the saddle point, S,. In the end wall region, two
legs of the horseshoe vortex, Flp and 11„ are formed around the blade.
The pressure side leg (H) is moved over towards the suction side of
the adjacent blade by the paccage vortex, which feeds into the flow
causing it to develop into a large vortex. The suction side leg (H s)
tends to diminish as it flows around the blade because of its opposite
sense to that of the passage vortex. The passage vortex sweeps across
to the suction surface some distance from the stagnation region. The
affected zone on the blade appears to have an almost triangular shape,
the trailing edge point of the region, N sb is at about 12.5 percent of
the passage height above the end wall. Outside the triangular region,
the streamlines near the suction surface are skewed toward the middle
span of the blade, and the streamlines near the pressure surface are
slightly inclined toward the end wall.
6
7
8
9
5
30.0 40.0 81.0 97.0 113.0
0.047 0.543 1.099 1316 1333
Fig 4 Thwerse measuring planes
1.11 t=71.45mm U1
From flow visualization results with air injection from hole 1-9, it
can be seen that air injection has few effects upon the streamline
distribution on the end wall. In addition for air injection from hole 1,
Fig. 5 Plan view of cascade test section
4
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TE
I
Mid span
r1/17.1r
ass&
i
id
s
s
1
_T
I .1.• ••• I
.....
S
S
"
"
;
;
......
,
•
•
,.11aarri
...
...
•-..;
midspan
'''
I.
;
I
1
1)
I
h- -
- )°14'
14
Ns.
—
End wall
A2
midspan
•
Fig. 7 Flow visualization results and the schematic drawing of flow field structure in the cascade passage
2,7-9 on the pressure surface, the distributions of the streamlines on
wall without air injection, N52 is located at about 10, 7.5 and 6.25
percent span with air injection. This shows that air injection on the
suction side of the blade may affect the development of the passage
the suction surface are not affected significantly, and it is the same for
the distributions of the streamlines on the pressure surface with air
injection from hole 3-6 on the suction surface. So only the flow
vortex, and at the same time, a triangular-shaped region uncovered by
the injected air always exists on the suction surface due to the
visualization results on the pressure surface with air injection from
hole 1,2,7-9 and the results on the suction surface for the cases of
hole 3-6 injection are presented in Fig.8.
existence of the passage vortex. For air injection from hole 1, 7-9 on
the pressure side, it is interesting to note that the distributions of the
ink drops on the blade surface are disordered downstream of the holes
As shown in Fig.8, the distributions of streamlines near the blade
up to the trailing edge, especially injecting from hole 1. The
surface are different compared to those without air injection. The
separation lines of the kidney-shaped vortices can not be seen clearly.
One explanation about these results may be that the air injected from
separation lines of the kidney-shaped vortices resulted from the
reoriented outgoing vortex rings issuing from the injection holes can
the holes on the pressure side attaches to the blade surface rapidly,
then the injected air/mainflow mixing process basically occurs in the
be seen downstream of the hole exit with air injection from hole 2, 46, existing on the blade surface up to the trailing edge. This means
boundary layer. To a certain extent, the occurrence of the mixing
that the original two-dimensional flow field near the blade surface
process means the existence of the kidney-shaped vortices, therefore
becomes three-dimensional due to air injection, the kidney-shaped
the kidney-shaped vortices may always exist downstream of the
vortices may always exist downstream of the injection holes and mix
out with the wake at the cascade exit under the present experimental
conditions. For the air injection from hole 4-6 on the suction side, the
injection holes with air injection from the pressure side. Compared
the visualization results of pressure side injection to that of suction
side injection, one may conclude that under the present experimental
separation line of the passage vortex, indicated by A l -Ns, on the
suction surface, is skewed toward the end wall. Compared to the
location of N s, lied at about 12.5 percent span apart from the end
conditions, the mixing process between the injected air and mainflow
occurs farther above boundary layer with suction side injection.
5
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Midspan
—"Mole 2
IT LE
Hole 1 Midspan
Midspan
TE LE
Hole 7,
s.m
A.
TE
LE T
10.1 •
r_=.
:66.4.•;•4a
•
•
•
Nsy
e'Z
TE
End wall
Hole 3
PS
Mids
TE
-1
_44.)
si
TE
..
E
vr
1..;.„14.
.
Sao
aS
m..,..e........_____
_--- Th
-- ,..lea-- ■-n--
N 5L.
____
_.
-
0
74."
. -.1•6—.
- - --'. .
abblft..
6
End wall
5101;.:
-- —
r
illinIMM
-=31A4....t"--
A I SS
.
'
.
.
.
I
1
•
'
.
I
"
_.„..
.I
.
SS End wall
6
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.
I •
. ”jr 1: 1 ...rr
Fig. 8 Flow visualizalion results on the blade surface with air injection
.
.
•I .
I
■
I. ..
1
'T
Fig 9 Schematic drawing of the flow field structure in the turbine cascade passage with air injection
"preliminary impact" process between the injected air and the
mainflow, therefore the changes of pressure distribution are similar to
that of hole 7-9 injection. The situations are different with air
injection from hole 1, the low-pressure region exists obviously
downstream of the holes. This is associated with the existence of
decelerating flow zone on the pressure surface near the leading edge.
For the air injection along the mainflow from hole 4-6 on the suction
side, the significant pressure decreases downstream of injection holes
indicate that the kidney-shaped vortices resulted from the reoriented
outgoing vortex rings issuing from the injection holes tend to move
downstream at farther distance from the blade surface. Therefore the
low-pressure zone under the bending-over injected air is significant.
During the experiments, it is found that if the ink drops are spread
very close to the injection hole exit, they flow against the mainflow
direction. It means that the recirculating mainflow infiltrates the
region under the injected air due to the formation of low pressure
zone downstream of the holes. Unfortunately, the flow visualization
experiments can not pick these phenomena up accurately.
From the results and the discussion described above, the
schematic drawing of the three-dimensional flow field structure in a
turbine cascade with air injection is shown in Fig.9.
The
Effects of Air Injection on Pressure Distribution
pressure distributions along the midspan profile are shown in Fig.10
with/without air injection. The results show that in contrast to the
pressure side injection, the changes of pressure distribution are
dependent mainly on the amount of injected air and the locations of
injection holes with air injection from hole 3-6 on the suction side.
The results also show that the surface pressure decreases owing to
the existence of low-pressure zone downstream of the injection holes
are more significant than the pressure increases caused by mainflow
stagnation upstream of the holes. So the traverse pressure gradient in
the passage decreases slightly upstream of holes and increases clearly
downstream of them with suction side injection. For the pressure side
injection, the traverse pressure gradient increases upstream of holes
and decreases downstream of them, but the changes are not clear
except hole 1 injection.
For the air injection along the mainflow direction from hole 7-9 on
the pressure side, the injected air may attach to the blade surface
rapidly, and then the low-pressure zone can not be seen clearly
downstream of the holes. Although the mixing process may basically
occur in the boundary layer as shown in flow visualization, the
effects of air injection are not obvious owing to the weaker mixing
process and to the diffusion flow pattern on the blade pressure
surface. When the air is injected against the mainflow from hole 2,
the intensity of the injected air is weakened by the strong
Fig.11(a) shows the pressure contours on the end wall without air
injection. In order to demonstrate the effects of air injection on the •
end wall pressure distributions clearly, the contour plots are presented
in their difference forms (All,) between 0 and 1.2 percent injection.
7
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1.0
1.0
0.5
0.5
Ha
Hs
0.0
0.0
No injection
Bole 1
- 0.5
1.0
.
.
.
.
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cax
0.5
1.0
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cax
Hole 1
0.5
0.5
Hs
Hs
0.0
0.0
- 0.5
1.0
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cax
0.5
1.0
0.5
0.5
Hs
Ha
0.0
0.0
-0.5
0.5
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cax
Hole 2
Hole 3
1.0
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cox
0.5
0.5
Hs
Hs
0.0
0.0
- 0.5
1.0
0 0 0.2 0.4 0.6 0.8 10
Z/Cax
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cax
1.0
0.5
(d)
0.0 0.2 0.4 0.6 0.8 1.0
Z/Cax
Symbol:
0.5
13.0%
Hs
13=1.2%
0.0
- 0.5
133.6%
Mg. 11 Changes in pressure distribution on the end wall for hole 134,9
injection
0.0 0.2 0.4 0.6 0.8 1.0
2/Cox
Fig.10 Pressure distribution on surface for hole 1-9 injection
8
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esitettIS
saminceskammi
Plane I
Plane 2
Plane 3
4711,
, %innt ' Iii; ,
S.
a.
a d-M
„:„
\
''
412
INNV,W0.
I
Ira/.
1ff I.
111
12-1t
.
Plane 4
Plane 5
:,
;
.--
\ NO:::
4Wtriii#1
WV00‘1 1111.
WW0Ilitee
.....
• ....... lilt
f1l1/1/111,,
w
II 11111“,
1
,•.
n
.
.....?:,..
liL\
', 141-7
Plane 6
`
Ic ..
hi -
,
va ...
i;
Plane 8
Plane 7
Plane 9
Fig. 12 Loss contours and secondary flows without injection at plane 1-9 (Left-SS, Right-PS)
gIMMIMSItttgM
....,
i
1
Plane 3
iim=apaawasA
Fig. 1.3 Loss contours and secondary flows for hole 2
injection at plane 2 (13=11%, Left-SS, Right-PS)
Plane -4-111
Plane 5
Plane 6
—
Fig. 14 Energy bra dianges for hole 2 injection at plane 3-6 03,,,,„,)
the same time, thus the injected air may affect the boundary layer in
the end wall.
rates with air injection from hole 1-3,4,9, as shown in Fig.12(b)-(f).
In the contour plots of a.H„ solid lines indicate pressure increase
with air injection, and dashed lines indicate pressure decrease. The
measured data show that the influences of air injection against the
mainflow direction from the holes located at the leading edge on the
pressure distribution are visible in contrast to the other tested
conditions. This means that although the intensity of the kidneyshaped vortices is weakened due to the "preliminary impact" process
between the injected air and the mainflow, their scales are enlarged at
Overall View of the Internal Flow and the Associated Energy
Loss Inside the Cascade Passage Fig.I2 shows the development
of secondary flow vectors and the energy loss in the cascade passage
without air injection by using the experimental data at different
measuring planes. Only the passage vortex is seen clearly, and other
vortices can hardly be seen. As the passage vortex develops, low
energy fluids of the end wall boundary layer roll up onto the blade
9
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II
I
. ......
,
•
•••••
••••- 1
•
........ •ener
//”.•••
Illen I I
LW/ I
Plane 3
Plane 5
Plane 4
Plane 6
Plane 3
Hole 2
1 :-,‘'
'
-
A
Plane 5
Plane 4
Hole 1
••••
A
..'•5;
,
...... •
••
......'
• ••
......
V' • • • • ......
__. • • ......
.-1
-••••• ' • ....
....
I
?;""..
i
Plane 3
0.i;; ;: f
N41
Plane 6
Plane 5
Plane 5
Plane 6
Plane 5
Plane 6
Hole 9
Hole 4
Hole 3
Fig. 15 Changes in secondary flows for hole 1-3 injection at plane 3-6 and for hole 4,9 injection at plane 5,603,,,, m)
Plane 4
,852
)
i
c''..;1
Wirfed
vt,
'011
„„ ..
• -v.v.., 11 111
I
AS
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•••, ,, • • • •„
N
i
••,, ..,•
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' / • •• •1%, \ V • • Ir. ,•••• I .NNV . ■
0.• ..... ‘•••
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i
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Hole 1
Hole 5
Hole 2
Hole 3
Hole 7
Hole 6
Fig. 16 Changes in secondary flows for hole 1-8 injection at plane 7(80
10
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I
I
... ,
11W:!11i :11;
'•' I'I
Hole 4
Hole 8
,
\.7
Hole 2
Hole 7
Hole 8
Fig. 17 Changes in energy loss for hole 1-8 injection at plane 7 (
1 .0
1.0
0.8
0.8
0.6
Y/11
0.4
0.6
Y/H
0.4
1.0
t
1.0
1.0
0.8
0.8
0.8
0.6
Y/H
0.4
0.6
Y/H
0.6
Y/H
0.4
?
4)
Symbol:
Hole 2
Hole I
0.2
0.2
0.0
0.00 0.07
•
0.14
•
0.0
0.00 0.07 0.14
0.4
Hole 3
Hole 4
11),
1
0.2
0.2
0.0
0.00 0.02 0.14
0.0
0.00 0.07 0.14
1,
6
* 1:13.0%
o
11=1.2%
[3.6%
0.2
0.0
0.00 0.07 0.14
t7
17
Fig. 18 Energy loss distribution in spanwise at the outlet plane 7 with injection from hole 1-3,4 and 9
1 .0
1.0
1.0
1.0
1 .0
0.8
0.8
0.8
0.8
0.8
0.6
Y/H
0.4
0.6
Y/H
0.6
Y/H
0.6
1/H
0.4
0.4
0.4
•
0.2
Hole 9
Symbol:
0.6
Y/H
•
0.4
0.2
'Hole I
0.2
Hole 2
0.0
0.0
200 24.0 28.0 320
200 24.0 28.0 320
0.2
Hole 3
0.0
200 24428.0 32 0
0.2
•
Hole 4
0.0
1"-20 0 24028.0 320
117
*
o
p=1.2%
[3=0.6%
0.0
200 24.0 28.0 32 0
417
Fig. 19 Flow angle distribution in spanwise at plane 7 with injection from hole 1-3,4 and 9
suction side, as seen from the energy loss contours. Downstream of
the cascade exit (planes 7-9), the low energy fluids over the suction
The energy loss contours and secondary flows at plane 2 with air
injection from hole 2 are shown in Fig.13. Comparing with those in
side separate from the blade trailing edge to form cascade wakes.
Fig.12, it is found that although air is injected against the mainflow,
11
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the influences of injected air on energy loss and secondary flows at
farther upstream planes of the injection holes can be ignored.
Therefore only the results of the secondary flow vectors and energy
loss at plane 3-9 are given in their difference forms (AV, and A)
between 0 and 1.2 percent injection rates.
remarkable increase of the energy loss, especially near the midspan.
From another viewpoint, for hole 1, 2 and 9 injection, the air is
injected into the zones of low mainfiow velocity, thus generates low
mixing losses. For hole 3 and 4 injection, the air is injected into high
velocity regions, thus causes high aerodynamic mixing losses.
The changes in energy loss with air injection from hole 2 at plane
3-6, A are shown in Fig.I4. A loss increase area (solid lines) is
seen clearly near the pressure surface at plane 3 owing to the
interaction between the injected air and the mainflow. This zone
becomes invisible at downstream planes.
Fig.19 shows the changes in the mass-averaged cascade outlet
flow angle obtained at plane 7. The injection from the suction side
tends to increase the exit flow angle, while the injection from
pressure side tends to decrease the angle. But the mass-averaged
changes are relatively small and the effect of coolant on the flow
angle need not to be considered if the injection rate is not very big.
,
The subtracted secondary flow vectors AV, at plane 3-6 with air
injection from hole 1-3 and at plane 5, 6 with air injection from hole
4, 9 are shown in Fig. 15. For the air injection from hole 1 and 2 lied
on the pressure surface, the changes of the secondary flow vectors at
plane 3-6 are always visible near the pressure side along the whole
blade height This may show that the mixing process always occurs in
the passage. It is interesting to note that the rotational direction of A
V, in the corners between end walls and pressure side is opposite to
that of passage vortex, which means that the passage vortex is
weakened by the interaction between the injected air and the
mainflow. For injection from hole 3 located at the suction surface of
the leading edge, the rotational direction of V, in the corners
between end walls and suction side is the same as that of passage
vortex, and this means that the passage vortex is strengthened. The
changes of the secondary flow at plane 3-6 can also be seen near the
suction side along the whole blade height. When the air is injected
along the mainflow from hole 4 and 9, the situations are similar to
those of the air injection against the mainflow.
Conclusions
An experimental investigation into the effects of air injection on
the aerodynamic performance and three dimensional flow field
structure in a linear cascade with typical guide vane profile is made.
The main results are as follows:
I. For the suction side injection, the variations of the surface
pressure distribution are dependent chiefly on the amount of injected
air and on the locations of injection holes, and the low-pressure zone
downstream of injection holes can be seen clearly. The injection from
the blade pressure side alters the surface pressure distribution slightly.
In the great majority cases, the surface pressure decrease owing to the
kidney-shaped vortex is significant compared to the increase due to
the mainflow stagnation owing to the air injection.
2. For the air injection against the mainflow from the holes on the
leading edge, although the intensity of the kidney-shaped vortices is
weakened due to the "preliminary impact" process, their scales are
enlarged at the same time. Therefore the influences of air injection on
the end wall pressure distribution are visible in contrast to the other
tested conditions.
Fig.16,17 show that the effects of air injection from hole 1-8 on
the secondary flows and the energy loss at plane 7 are significant.
The present results indicate that the injection increases the loss at
plane 7 located after the cascade exit and leads to a disordered
distribution of the subtracted secondary flow vectors. One may draw
a conclusion that the kidney-shaped vortex may always exist near the
blade surface in the passage and mix out with the wakes at the
cascade exit, which leads to the changes of the aerodynamic
parameters at the cascade outlet.
3. The air injection on the suction side may affect the development
of the passage vortex, a triangular-shaped region uncovered by
injected air always exists on the suction surface due to the existence
of the passage vortex, the mixing process occurs farther above
boundary layer. For pressure side injection, the injected air attaches to
the blade surface rapidly, the mixing process basically occurs in the
boundary layer.
Fig.18 shows spanwise distribution of pitchwise mass-averaged
energy loss at the cascade downstream plane 7 for five selected
injection holes: hole 1-4, and 9. For hole 1 injection, the loss
increases first near the end walls where corresponds to the height of
passage vortex and then along the whole span at 0.6 and 1.2 percent
injection rates. For hole 2, owing to the "preliminary mixing" as
described before, the loss changes are not significant. For hole 4, the
loss increases along the whole height, while hole 9, the effects of the
air injection is neglectable. For hole 3, the loss increases more rapidly
and clearly, it means that the intensity of the kidney-shaped vortices
is stronger than the other cases, and the violent mixing process
among the injected air, wakes and passage vortex causes the
4. For the pressure side injection, the passage vortex is weakened
by the interaction between the injected air and the mainflow, this
causes a smaller amount of low momentum fluids to migrate into the
corner region between suction surface and end wall. For the suction
side injection, the passage vortex is strengthened and pushed away
from the injection surface.
5. Although the scale and intensity of kidney-shaped vortices are
different when air is injected from various positions, these vortices
may always exist near the blade surface, and mix out with the wakes
12
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on Aerodynamic Performance of a Turbine Cascade", ISABE 89-7040, Bangalore,
pp. 397-404.
at the cascade exit, which leads to the changes of the aerodynamic
parameters at the cascade outlet.
Moussa, Z.M., Trishka, J.W., Eskinan, S., 1977, 'The near Field in the Mixing
of a Round jet with a Cross-Stream", Journal of Fluid Mechanics, vol. 80, pp. 4980.
6. The energy loss increases near the blade surface from which air
is injected due mainly to the mixing process and to the formation of
kidney-shaped vortices.
Sieverding C.H., 1984, "Recent Progress in the Understanding of Basic Aspects
of Secondary Flows in Turbine Blade Passage", ASME Journal of Engineering for
Gas Turbine and Power, vol. 107, pp. 248-257.
7. The overall changes of the mass-averaged cascade outlet flow
Sieverding C. H., Arts, T., Demos, R., Martelli, F., 1994, 'Investigation of the
Flow Field Downstream of a Turbine Trailing Edge Cooled Nozzle Guide Vane",
ASME Paper 94-GT-209.
angle due to the injection are in general very small in the present
cascade.
Wang, RP., Olson, S.J., Goldstein, RI, Eckert, ER.G., 1995, "Flow
Visualization in a Linear Turbine Cascade of High Performance Turbine Blades",
ASME Paper 95-GT-7.
Acknowledgement
This research project has been supported by the China National
Wilfert, G., Fourier, L., 1994, "The Aerodynamic Mixing Effect of Discrete
Cooling Jets with Mainstream Row on a Highly Loaded Blade", ASME Paper 94GT-235.
Science Foundation. The support and the permission for the
publication are gratefully acknowledged. We would also like to thank
Ms. Song Yanping, Mr. Xu Wenyuan and Mr. Han Wanjin for their
Yamamoto, A., Kondo, Y., Murao, R., 1991, 'Cooling-Air Injection into
Secondary Flow and Loss Fields Within a linear Turbine Cascade", ASME Journal
of Turbomachinvy, Vol. 113, pp. 375-383.
assistance in conducting the experiment.
Yang, H., Chen, F., Gong, C.Z., Wang, Z.Q., 1997, "Investigation of Cooling-Air
Injection on the Flow Field within a Linear Turbine Cascade", ASME Paper 97GT-520.
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