The American Society of Mechanical Engineers
ASME TURBO EXPO
June 14-17, 2004 Vienna, Austria
GT2004-53961
EXPERIMENTAL INVESTIGATION OF AIRFLOW AND SPRAY STABILITY IN AN AIR-BLAST
INJECTOR OF AN INDUSTRIAL GAS TURBINE
Andrei Secareanu
Dragan Stankovic
Laszlo Fuchs
Vladimir Milosavljevic
Jonas Holmborn
Demag Delaval Industrial Turbomachinery AB
SE-612 83 Finspong, Sweden
Division of Fluid Mechanics
Lund University of Technology
SE-221 00 Lund, Sweden
ABSTRACT
The airflow field and spray characteristics from an air
blast type of injector in an industrial gas turbine (GT)
combustor geometry have been investigated experimentally
and numerically. The studied injector is a conventional liquid
fuel injector used in the industrial gas turbine GT10B. The
flame in the current combustor is stabilized by a highly
swirling flow. The stabilization of the flame is strongly
dependent on the stability of the flow field out from the
injector and into the combustor. Liquid fuel spray formation
in the current type of injector is highly dependent on the
airflow from the internal swirler, which supplies the shear to
break the liquid film, and form the spray.
Experiments were performed in a Perspex model of a
12° sector of the combustor with airflow scaled to
atmospheric conditions. The geometry was comprised of the
air section including the full primary zone, injector,
combustor swirler, front panel and primary air jets. The flow
field was visualized using particles that were illuminated by a
laser sheet. Quantitative characterization was done using
LDA. The airflow field was characterized by the mean flow
pattern covering the full cross-section of the flow field and
additional long time measurements at a number of locations
in order to capture frequency content of the flow. Isothermal
spray measurements were performed in an unconfined
geometry including the injector, swirl generator and front
panel. The spray uniformity was qualitatively investigated
using video camera and quantitatively characterized by PDA.
The studies of the flow field and fuel atomization
(droplet size and density) under different conditions are
summarized below.
INTRODUCTION
The technical development of industrial gas turbine
gained momentum in the past decades. In parallel to the
technical development, new environmental restrictions have
been issued. These restrictions increase considerably the
burden on the designer of gas turbine combustors. Greater
power-density, increased output, and cleaner operation, have
been the central design goals for gas turbines over the past 25
years. In spite of the design complexity, gas turbines offer
some clear advantages: high efficiency, low emissions, low
installed cost and low-cost power generation.
Even if the gas turbine emissions levels are already
relatively low, one aims to further reduce these emissions.
This development is driven by more and more stringent
requirements by the authorities. These requirements are
aimed at addressing ecological and environmental concerns
[1], [7]. One way to decrease the emission level is to reduce
the total fuel consumption which is directly related to
improved engine efficiency. Another possibility is to reduce
the temperature peaks in the combustion chamber and
thereby reduce the formation of thermal NOx [7]. A global
reduction of combustion temperature is, however, not sought,
since this would lead to the loss of the efficiency of the GT.
Combustion in-homogeneities are also often associated with
emission of un-burnt hydro-carbons (UHC). Thus, the
homogeneity of the mixture prior to combustion is a central
issue for controlling levels of emissions. When using liquid
fuels, the atomization process and the structure of the
turbulent flow field become critical factors for the
combustion process.
The fuel/air mixing becomes a key factor that determines
the levels of performance and emissions of a GT. In addition,
one has to support flame-holding. Enhancing mixing and
flame-holding can be achieved by introducing air (and
possibly also fuel) with swirl. Swirling enhance fuel-air
mixing, and flame anchoring in the proximal part of the
combustion chamber [3]. Swirling flows are generated by
three principal methods: guide-vanes (axial swirler),
tangential inlets (radial swirler) and directed rotation. Here,
swirl is introduced through the guide-vanes in the flow
stream. Experimental and theoretical studies show that
swirling motion has major effect on flame. A major draw
back of flame holding by swirl as compared to introducing an
object, is due the lower stability of the flame. If the swirl is
large enough a so called vortex break-down occurs
[1],[4],[5]. This implies that a recirculation region is formed
around the axis of the jet. At the tip of the recirculation zone,
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Copyright © 2004 by ASME
there is a stagnation point that marks also roughly the tip of
the flame. Vortex breakdown is inherently unstable, so that
the recirculation bubble and the stagnation point can move in
any direction: axially, radially and azimuthally. The flow
and (mean) flame position are highly sensitive to small
changes in the inlet condition [2], [6]. This high sensitivity is
a major drawback and makes the optimal design of swirl
stabilized burners very challenging.
In the following Section we describe our experimental
studies of the GT10B burner. We consider the aerodynamic
stability of the flow and vortex breakdown which is formed
by the three co-annular swirling jets of the burner.
THE EXPERIMENTAL RIG
The experimental rig is built around an existent burner of
a gas turbine (GT10B) shown in Figure 1. Experiments have
been performed in a Perspex made enclosure, corresponding
to a 120 sector of the combustor. The airflow is scaled to
atmospheric conditions. Three measuring points are marked
in the figure and Points 1-3.
Figure 3: The experimental rig, viewed from the free-end
of the rig.
BURNERS GEOMETRY
The burner is composed of three co-axial inflows,
delivering different portions of the total mass flow,
respectively. A more detailed view of the burner is given in
Figures 4. Swirl is formed by the vanes placed in the three
inlets. All three jets co-rotate. Fuel is injected between the
middle and the inner inlets. The liquid fuel is introduced on
the lip seen in Figure 2b. The thin fuel layer is broken up by
the strong swirling air-jets.
Figure 1: The burner configuration.
(a)
The model includes the air section with the full primary zone,
injector, combustor swirlers, front panel and primary air jet,
as shown in Figures 2 and 3.
176
Z X
160
Y
118
(a)
(b)
Figure 2: The shape of the full combustor (a), a sector of
combustor is approximation a trapezium (b).
The shape of the experimental rig is a parallelepiped (Figure
2). The base is a trapezium. The angle between the lateral
part and the parallel surfaces are 800 and 1000, respectively.
The GT combustion chamber is of annular type and the
sector which we have been studying corresponds to a single
burner sector. As shown in Figure 2a. The length of the
experimental rig is 500 mm. The lateral walls have dilution
holes, as shown in Figure 2b. The total mass flow for the
cases reported herein was 200 grams/second.
(b)
Figure 4: The sketch with the mass-flow repartition
through the swirl generators (a). A frontal view of the
first two swirl generators and between them the inlet for
fuel (b).
MEASUREMENT TECHNIQUES
Our measurement device consists of a Dantec twocomponent LDA/PDA system. It has been used to determine
the turbulent velocity field. The blue laser beam 455 nm and
green laser beam 514.5 nm of an Ar-Ion laser (350 mW) have
served as light source. Each color has been used to measure a
single component of the velocity. The laser beams are split
and focused by a front lens of 500 mm focal length. A
frequency shift of 40 MHz has been introduced to one of the
beams of each color. The system has been running in a backscatter mode and a digital auto-correlator has been used to
evaluate Doppler signal. The light scattered by the seeding
particles (TiO2) are captured by the receiving optics which
also separates the scattered light by using color filters. Photo
multipliers convert the light energy to electrical signals.
The sampling time during measurement depends on
the flow velocity at each measurements point. Data rate has
been in the range of 500-4000 Hz. The flow direction is
distinguished through a Bragg cell of a 40MHz frequency
shift on the two (blue and green) beams. The LDA technique
has the advantage that it is non-intrusive, it requires no
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Copyright © 2004 by ASME
RESULTS AND DISCUSSION
We consider the statistics (mean and rms values) of the
turbulent flow field. The flow field had been traversed and
instantaneous data was gathered at the predetermined
sampling points. In addition to the first and second moments
of the instantaneous data, we consider also the frequency
content at some selected locations. The spectral content can
indicate the presence of aero-dynamical instabilities and also
indicate how these frequencies interact with turbulence.
First we consider the flow field in one (denoted in the
following as the XZ-) plane (see Figure 2b for notation). The
mean axial and radial velocity components along the
centerline (of the burner) are given in Figure 5. The X-range
for which the axial component is negative, characterizes the
region of the recirculating zone (on the axis). For the given
case, this distance equals to 1.7 D, where D is the outer
diameter of the burner. The vortex breakdown in this case is
of a “bubble” type, which means that the flow accelerates
behind the recirculation bubble. For smaller enclosures or
larger swirl numbers, one may find vortex breakdown of a
cone shape. In such a situation, the flow does not accelerate
behind the recirculation zone, but it continues primarily
along the walls of the enclosure. In this case the maximal
mean velocity shows a strong negative velocity of u min =9
m/s at about 1.3 D downstream of the burner inlet. The
radial velocity along the center line varies around 0 m/s in
the whole range that has been measured (i.e. 0< X <2.5).
The mean of the fluctuations (rms of turbulence) are
shown in Figure 6. Enhanced turbulence production can be
found at the end of the recirculation zone (note the larger
shear as expected in such regions). Thus, turbulence level
increases gradually from the inlet until it reaches its peak
towards the end of the recirculation zone, thereafter the
turbulence intensity decreases gradually.
It should be stressed that the holes (seen in Figure
2), are placed asymmetrically. Hence, the whole flow field is
asymmetric. This is observed in Figure 7, where the axial
velocity profiles at different distances from the nozzle are
given. These velocity profiles give the shape of the
recirculation zone. The width of the recirculation zone is a
little bit more than 2 D and its length is about 1.7 D
downstream the inlet.
The peak values for the magnitude of the velocity and
corresponding fluctuations along different axial lines are
located at the shear-layer that is formed by the swirling jets.
Figures 7 and 8 depict the mean and the rms distribution,
axial and radial velocity along center line vs distance from injector (XZ)
4
2
velocity (m/s)
MEASUREMENT ACCURACY
The accuracy of the system is a function that depends on
several variables, such as laser power, seeding material,
optical arrangement, measurement environment. The errors
given by the LDA system is estimated to be in the range
± 1% [8]. Additional error may occur due to limited number
of samples, as well as systematic errors not related to the
LDA system. Altogether, we estimate the total error, due to
the system and due to the number of samples, to 6% and
very close to the wall where the data rate is lower the errors
increase, but still less then 10%.
respectively. The shear layer of the swirling jets is
responsible for the production of the turbulent fluctuations,
which is observed in the rms values in Figure 8.
Corresponding data have been measured for the YZ
(orthogonal to the XZ-plane). Figure 9 and 10 depict the
mean and the rms of the axial velocity component along the
axis. These measurements have been done independently of
the previous measurements and are given for comparison
with the results presented in Figures 5 and 6, respectively.
The geometrical asymmetry of the rig can be seen in the
axial velocity along the burner axis at different distances
from the centerline (in the YZ-plane). Figures 11 and 12
depict the variation of the mean and rms axial velocity
component at these locations. The measured data is used to
assess the mass-flow which has also been used to estimate
measurements errors. One may note the production of
turbulence due to the presence of the shear-layers.
0
-2
axial velocity
radial velocity
-4
-6
-8
-10
0,5
0,75
1
1,25
1,5
1,75
2
2,25
2,5
X (diameter)
Figure 5: The variation of the mean values for the axial
and radial velocity component along the centerline (XZplane).
RMS axial and radial velocity along center line vs distance from
injector (XZ)
7
6
velocity (m/s)
calibration, and it has well-definer directional response, high
spatial and temporal resolution, and allows for simultaneous
two-component measurements [8].
5
axial velocity
radial velocity
4
3
2
1
0
0,5
0,75
1
1,25
1,5
1,75
2
2,25
2,5
X (diameter)
Figure 6: The variation of the rms values for the axial
and radial velocity component along the centerline (XZplane).
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Copyright © 2004 by ASME
axial velocity profiles at different distances from injector (YZ)
axial velocity profiles at different distances from injector (XZ)
15
15
0.74D
10
0.92D
0.7D
velocity (m/s)
velocity (m/s)
10
0.88D
5
0.926D
1.296D
1.481D
0
2.037D
1.11D
5
1.29D
1.48D
0
1.66D
1.85D
-5
2.03D
2.222D
-5
2.22D
-10
2.4D
-10
-1,5
-1
-0,5
0
0,5
1
-15
-1,5
1,5
-1
-0,5
X (diameter)
0
0,5
1
1,5
X (diameter)
Figure 7: The variation of the mean axial velocity profiles
at different distances from injector (XZ-plane).
Figure 11: The variation of the mean axial velocity
profiles at different distances from injector (YZ-plane).
RMS axial velocity profiles at different distances from injector (XZ)
RMS axial velocity profiles at different distances from injector (YZ)
7
8
7
0.74D
0.88D
5
0.926D
1.296D
4
0.92D
6
0.7D
velocity (m/s)
velocity (m/s)
6
1.481D
2.222D
1.11D
1.29D
5
1.48D
4
1.66D
1.85D
3
2.03D
2.22D
2
3
2.40D
1
2
-1,5
-1
-0,5
0
0,5
1
0
-1,5
1,5
X (diameter)
axial velocity along center line vs distance frominjector (YZ)
4
2
velocity (m/s)
0
-2
axial
velocity
-4
-6
-8
0,75
1
1,25
1,5
1,75
2
2,25
2,5
X (diameter)
Figure 9: The variation of the mean values the axial and
radial velocity component along the centerline (YZplane).
RMSaxial velocity along center line vs distance frominjector (YZ)
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velocity (m/s)
6
5
4
RMSof axial velocity
3
2
1
0
0,5
0,75
1
1,25
1,5
1,75
-0,5
0
0,5
1
1,5
X (diameter)
Figure 8: The variation of the rms values axial velocity
profiles at different distances from injector (XZ-plane).
-10
0,5
-1
2
2,25
2,5
X(diameter)
Figure 10: The variation of the rms values for the axial
and radial velocity component along the centerline (YZpane).
Figure 12: The variation of the rms values axial velocity
profiles at different distances from injector (YZ-plane).
Another major objective of our measurements has been
to determine the aero-dynamical instability of the vortexbreakdown. This was done by considering the spectral
content of the measured velocity field. The flow in the rig is
turbulent (Re is the range of 32000 and 45000). The turbulent
spectrum is expected to behave according to Kolmogorov’s
theory. In addition to that part of the spectrum, we expect to
observe the coherent motion associated with the instability of
the re-circulating zone and the shear-layer instability. We
consider the first sampling point (see Figure 1) placed in the
shear-layer (Point-1), on the centerline of injector (Point-2)
and near the combustor wall (Point-3). The data has been
collected for the two directions (vertical and horizontal).
Point-1 is located at 0.75 D downstream of the injector and
0.55 D away from centerline, in ZY-plane. Point-2 is located
at 1.4 D downstream of the injector on the centerline and
Point-3 is located at 1.4 D downstream of the injector and at
0.18 D close to the combustor wall, in the ZX-plane.
The conditions have been the same during all the
measurements. For the spectral analysis 100 000 samples or
90 seconds of recording is used. Figures 13-18 depict the
spectral content of the data at the three sampling points by
each of the two velocity components. At the end of the high
frequency one can observe the decay of the energy of the
smaller eddies. For the range of frequencies above 100 Hz,
the amplitude of the fluctuating energy decays in close
accordance to Kolmogorov’s theory (with a slope of -5/3).
The low frequency content is more intricate. In Figure 13 (at
Point-1, in the shear-layer), one may note the lowest
frequency at 8 Hz (Strouhal number of about 0.02). At Point2 one notes a 30 Hz mode, which we associate with the
motion of the recirculation bubble. In fact, one may observe
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Copyright © 2004 by ASME
Figure 13: Power spectral density of velocity fluctuations
for Point-1. (Axial velocity)
Figure 17: Power spectral density of velocity fluctuations
for Point-3. (Axial velocity)
Figure 14: Power spectral density of velocity fluctuations
for Point-1. (Radial velocity)
Figure 18: Power spectral density of velocity fluctuations
for Point-3. (Radial velocity)
several frequencies at this Point (Figures 15-16) in the range
of 5-20 Hz.
Point-3 is located close to the walls of the enclosure. The
level of perturbations in this point is attenuated by the wall.
Even at this location one may note the low-frequency
components, in addition to the turbulent spectrum.
Figure 15: Power spectral density of velocity fluctuations
for Point-2. (Axial velocity).
COMPUTATIONAL APPROACH
Numerical simulations have been carried out for the
burner under consideration. The computational box has been
simplified, eliminating the holes in the side-walls. The
computational problem uses a rectangular chamber with a
cross-section of 3x3 burner diameters and a length of 8
diameters [9]. The inlet conditions have been flat profiles
with a solid body rotation accounting for the swirl. Random
fluctuation has been added to the inlet. Such perturbations are
do not model turbulence since its spectrum differs widely
from that of turbulent field. The mean velocity profile at the
nozzle differs also from the one used in the calculations since
the inlet to the burner is curved and hence a strong secondary
flow is expected. Thus, the numerical results are used at this
stage for semi-quantitative purposes. The numerical
calculations use a high-order Large Eddy Simulation (LES)
approach. Further details are given in [9].
Figure 16: Power spectral density of velocity fluctuations
for Point-2. (Radial velocity)
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Copyright © 2004 by ASME
Figure 19 Comparison of the numerical results with
experimental measurements (XZ-plane)
Figure 19 depict the comparison of the experimental and
numerical results. One may observe a reasonable qualitative
agreement in terms of the location and extent of the shearlayer at different axial distances. One may note that the
results agree better down-stream of the burner. This is due to
the stronger dependence of the results in the proximal region
on the inlet boundary condition. A region of high sensitivity
is the recirculation zone. In this region the experimental data
is of lower quality due to the difficulties in seeding. The
recirculation zone is somewhat longer in experimental case
than in computational one. The differences in the
experimental and numerical results are mostly attributed to
the geometrical simplifications and the inlet boundary
condition used in the LES.
SPRAY MEASUREMENTS
Phase Doppler Anemometer (PDA) has been used to
measure velocity and the diameter of the droplets. The
measuring technique is based on the frequency- and phaseshifts in the light scattered by the droplets in the fringe
volume. Since this technique is based on measuring directly
the frequency shift which is directly proportional to the
droplet velocity, no calibration is required [11]. This is in
contrast to hot-wire (HW) techniques. The data rate is also
much higher as compared to Particle Image velocimetry
(PIV), though it may be lower than for HW. However, PDA
is less reliable in mass flux measurements [12].
In the experiments water has been used instead of diesel
for several reasons, namely: safety and convenience.
Difference in surface tension between diesel and water is
significant which results in larger droplets [13]. Larger
droplets on the other hand have larger momentum and hence
have longer relaxation time. It should be stressed that modern
GT has to be designed for using multiple fuels. The
experience with multiple fuels shows that some of these
differ widely in terms of surface tension. In addition, some of
the fuels have temperature sensitive surface tension.
Additionally, our results are aimed at understanding the
behavior of the burner and the use the data for validating
CFD results. For these reasons, water has been used rather
than a particular liquid fuel.
The rig, which has been used for LDA measurements,
turned out to be inadequate for the PDA (droplet sizing)
measurements. The very strong swirling motion entrains
large amount of incoming air into recirculation zones making
the flow to nearly attach to the front plate. When liquid fuel
is introduced into the rig the droplets quickly deflect in the
radial direction and ultimately many of them impinge on the
sidewalls.
The water droplets on the wall form a highly unsteady
film. This deposition of water film prevents the PDA laser
beam pair to form a steady measuring volume at the desired
point. Traveling trough the unsteady water film the laser
beams refract with different angles making them move in an
unsteady manner. The fringes pattern insides the measuring
volume is therefore unsteady, making the data collection
possible only intermittently. The wavy structure of the water
film acts as a lens, altering the path of the laser beams. This
in turn, alters the shape and intensity of the fringe pattern.
Therefore, on the transmitter sidewall, narrow slits in the
wall have been introduced. Through these slits the laser
beams can pass without the interference form the wall film.
The PDA investigations have been located to positions at
some distance from the wall. Due to the many difficulties that
have been encountered during the confined measurements,
we decided finally to use an unconfined rig for the PDA
(spray) measurements. For the LDA setup, the flow has been
generated by blowing air trough the nozzle. That proved to be
very convenient when using TiO2 seeding.
Figure 20 depicts the unconfined burner set-up. The
burner is placed in a Perspex box, which is equipped with
perforated plates. In order to make the flow in the box
uniform, air is supplied from the sides and it passes through
perforated plates before it enters the burner.
Figure 20: Sketch of the GT 10c injector rig setup for the
PDA measurements
Due to the fact that the receiver lens had a focal distance
of only 160 mm, it had to be positioned close to the spray.
Due to the impact of the high swirling flow of the droplets,
the receiver lens has been often covered with droplets. A
plate with purge air is placed in front of the receiver optics.
In order to maintain optical access, a hole is made in the
middle of the plate. Air blows on the side of the plate that is
not facing the flow and therefore the receiver lens is shielded
from the droplets while there is only a minimal influence on
the flow field itself.
Transmitting optics has a focal distance of 500 mm and
therefore stays out of the reach of the droplets. The original
Dantec PDA laser transmitter (20 mW, red 632 nm) with
focal length of 160 mm has found to be too intrusive. Thus, a
laser transmitter that is part of Dantec LDA equipment (350
mW, blue 455 nm) has been used. The original red protection
filters in front of the Photo-multiplier tubes has been
removed due to the different laser light wavelength.
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Copyright © 2004 by ASME
inner
swirler
inject ion
lip
middle
swirler
inner
sw irle
0,2
Mean axial velocity [m/s]
8mm dow n
20mm dow n
0,15
0,1
0,05
0
20
40
60
80
Radial distance from the center line [m m ]
8mm down
20mm down
30mm down
5
Figure 23: Axial fuel flux at three axial distances
2,5
0
-2,5
-5
0
20
40
60
80
Radial distance from the center
line [m m ]
Figure 21: Mean axial velocity of droplets at three axial
distances
Plots of the mean axial velocity are presented in the
Figure 21. It can be seen that at the air that is coming trough
combustor swirler makes the greatest influence on the
acceleration of the droplets. In the region from the center line
to injection lip recirculation zone is present with intensity
stronger close to the injector. Velocity profiles show the trend
of high peak at 8 mm from the injector, which afterwards
starts to spread as seen at 20 mm and spread even more while
moving outwards at 30 mm downstream of the injector.
Somewhat higher values of peak velocities at 20 mm than 8
mm can be explained that the core of the swirl is narrow
close to the swirl generator and that the measurement is made
slightly outside of the swirling jet.
inner injectio middle combusto
sw irle
sw irler n
r
sw irler
160
Sauter mean diameter [microns]
combustor
sw irler
0
combustor
swirler
7,5
injection middle
lip
sw irle
30mm dow n
Axial flux [cm3/cm2/s]
Both the transmitter and the receiver are placed on setoff beams, which have been attached to the traverse table.
The angle of 300 between the transmitter and the receiver has
been chosen in order to get the strongest signal from the
droplets. Traverse table is controlled manually with precision
of 1 mm.
The air has been supplied from the compressor and the
mass flow is measured using an orifice plate. Water mass
flow is controlled by a ball type valve and determined with a
rotameter. The accuracy of the rotameter is estimated to be 5
%. Water from spay has been collected into a vessel placed
1.5 m below the nozzle.
Operating conditions correspond to the “full load” and
have been scaled down to atmospheric conditions while
preserving the global air velocity and air to fuel ratio [13].
140
8mm dow n
20mm dow n
30mm dow n
120
100
80
60
40
20
0
The Sauter mean diameter (SMD) of the droplets is
presented in Figure 22. At the measuring plane at 8 mm
downstream of the nozzle, we can see that in the region up to
the combustor swirler droplet size is around 100 µm. Small
droplets that are traveling upstream in the recirculation zone
have no great impact on the average droplet size. There are
some very large droplets that penetrate the recirculation zone.
Further outwards the Sauter mean diameter of the droplets is
reduced (to around 60 µm) which is explained by the fact that
the droplet sizes reduce by the shear induced by the very
strong swirl. The measurements of the droplet sizes at
positions 20 and 30 mm downstream of the injector show
presence of large droplets, which are not able to follow the
high curvature of the flow. As one moves in the radial
direction, the droplets become smaller as secondary break-up
occurs.
The axial fuel flux is presented in Figure 23. The axial
flux of the droplets shows a trend of radial movement with
the axial distance. Flux peak at 20 mm downstream from the
nozzle shows values greater than at 8 mm downstream, due
to the steeper radial distribution. The flux peak tends to
flatten, producing a more even flux distribution further
downstream.
CONCLUSIONS
The present work has had the aim of characterizing the
flow of a co-annular GT burner under non-reacting flow
conditions. This data is now used to assess numerical
modeling of fuel/air mixing in GT burners. The recirculation
bubble turned out to be unstable. The motion of the
recirculation bubble is rather complex, and characterized by
several low frequency modes. The PDA data obtained in an
unconfined rig shows that the droplet size varies both radially
and axially. The mean droplet sizes (Sauter mean diameter)
increases initially with distance due to droplet coalescence.
0
20
40
60
80
Radial distance from the center line
[m m ]
Figure 22: Sauter mean diameter at three axial distances
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Copyright © 2004 by ASME
ACKNOWLEDGMENTS
The project was partially supported by Demag Delaval
Industrial Turbomachinery AB (DDIT), Finspång, Sweden
and by the Swedish Energy Agency (STEM). We thank the
staff of the Fluid Dynamics laboratory at DDIT for heir help
with the experimental set-up. Many thanks are due to SvenGunnar Sundkvist and Christian Troger at DDIT for their
critical comments to this manuscript.
[13] Jermy, M. C., Hussain, M. and Greenhalg, D. A.
Operating liquid-fuel airblast injectors in low-pressure test
rigs: strategies for scaling down the flow conditions, Meas.
Sci. Technol. 2003, Vol. 14, pp 1151-1158.
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