Proceedings of International Symposium on Visualization and Image in Transport Phenomena, Turkey, 14-19 Oct. 2001
SIMULTANEOUS VELOCITY AND
CONCENTRATION MEASUREMENTS OF A
TURBULENT JET MIXING FLOW
Hui HUa, Tetsuo SAGAb, Toshio KOBAYASHIb and Nobuyuki TANIGUCHIb
a
Department of Mechanical Engineering, A22, Research Complex Engineering Building,
Michigan State University, East Lansing, Michigan 48824, USA. Email:huhui@egr.msu.edu
b
Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, Japan
In the present paper, a method for the simultaneous measurements of
velocity and passive scalar concentration fields by means of Particle Image
Velocimetry (PIV) and Planar Laser Induced Florescence (PLIF) techniques
is described. An application of the PIV-PLIF combined system is
demonstrated by performing simultaneous measurements of velocity and
concentration in the near field of a turbulent jet mixing flow. The
distributions of the ensemble-averaged velocity and concentration, turbulent
velocity fluctuation, concentration standard deviation and the correlation
terms between the fluctuating velocities and concentration in the near field
of the turbulent jet flow are presented as the measurement results of the
simultaneous PIV-PLIF system.
KEYWORDS: PIV technique, PLIF technique, PIV-PLIF combined System,
Jet flow
INTRODUCTION
Simultaneous information of a passive scalar and velocity field is desirable in many
fluid flow investigations like mixing in combustion chambers or distributions of drugs in
biomedical applications. The possibility of measuring velocity and a scalar at the same
time with high spatial and/or temporal resolution is also of fundamental importance for
the validation and development of models of turbulence and turbulent mixing. For
example, in a turbulent jet mixing flow, the species concentration field is determined by
molecular diffusion and transported by the turbulent flow field. When considering the
Reynolds-averaged scalar conservation equation, the effects of turbulent transport appear
in terms of the correlation between the concentration and velocity fluctuations, i.e.
expressions such as u 'c' and v'c' . Experimental characterization of these correlation
terms is needed for the development and validation of physical models. This requires the
simultaneous measurements of the velocity and concentration fields.
With the rapid development of modern optical techniques and digital image
processing techniques, whole-field optical diagnostics, such as Particle Imaging Velocity
(PIV) and Planar Laser Induced Fluorescence (PLIF) techniques, are assuming everexpanding roles in the diagnostic probing of fluid mechanics. The advances of PIV and
PLIF techniques in recent years have lead them to be mature techniques for the wholefield measurements of velocity and concentration or/and temperature in an objective
plane or over a volume of an objective fluid flow. In the present paper, the development
of a high-resolution PIV-PLIF combined system, which can achieve the simultaneous
measurements of instantaneous spatial distribution of velocity and concentration in a
fluid flow, will be described. The PIV-LIF combined system is applied to do
simultaneous measurements of velocity and concentration in the near field of
a turbulent jet mixing flow. As the measurement results of the simultaneous
PIV-PLIF system, the distributions of the mean and RMS fluctuation of
velocity and concentration, will be presented, together with the correlation
terms between the fluctuating velocities and concentration in the near filed
of the turbulent jet flow.
EXPERIMENTAT SETUP AND TECHNIQUES
Figure 1 shows the schematically experimental set-up used in the present study. A test
circular nozzle (D=30mm) was fixed in the middle of a water tank
(600mm*600mm*1000mm). Fluorescent dye (Rhodamine B, concentration is about
0.3mg/liter) for PLIF or PIV tracers (hollow glass particles d=8 ~ 12μm) were premixed
with water in a jet supply tank, and jet flow was supplied by a pump. The flow rate of the
jet flow, which was used to calculate the representative velocity and Reynolds numbers,
was measured by a flow meter. A cylindrical plenum chamber with comb structures was
installed at the upstream of test nozzle to insure the jet flow to be fully developed and the
turbulent levels of the core jet flows at the exit of test nozzles were about 3%. An
overflow system was used to keep the water level in the test tank to be constant during
the experiment. In the present study, the investigation region is at the near field of the jet
flow (Y/D<5.0). The distance between the exit of the test nozzle and the free surface of
the water in the test tank is about 30D. Therefore, the effect of the water free surface in
the test tank on the vortical and turbulent structures in the near field of the jet flow is
negligible, and the jet flow exhausted from the test nozzle is considered to be a free jet.
During the experiment, the core jet velocities (U0) at the exit of the test nozzle was set to
be about 0.20m/s. The Reynolds numbers of the jet flow, based on the nozzle exit
diameter and the core jet velocity is about 6,000.
Pulsed illumination laser sheets (thickness is about 1.5mm) were generated by a
double-pulsed Nd:YAG Laser system (Quantel Inc.). The frequency of the double-pulsed
illumination is 10Hz. The pulsed illumination duration is 4ns, and power is 200
mJ/pulse. The time interval between the two pulses is adjustable, which is 3 ms for the
present study.
A simultaneous image recording system was designed by using optics and two highresolution CCD cameras (TSI PIVCAM10-30, 1K by 1K resolution), which was shown
schematically on the right upper corner of Fig. 1. Since the emission peak of Rhodamine
B is about 590nm, and the wavelength of the illuminating laser light scattered by the PIV
tracer particles is 532nm. Two kinds of optical filters were used to separate LIF lights
from scattered laser lights, and then recorded separately to obtain PLIF and PIV image
simultaneously. A bend pass optical filter (532nm±5) was installed at the head of the
camera #1, only the scattered laser light is transmissible to form PIV image on the CCD
sensor of the camera #1, and LIF light is blocked out. A high pass filter (>580nm pass)
was installed in the head of the camera #2 to filter out the scattered laser light
(wavelength 532nm). The LIF light (peak at 590nm) pass through the optical filter to
generate LIF image on the CCD censor of the camera #2.
Rather than tracking individual particles, an improved spatial correlation analysis
method, named as Hierarchical Recursive PIV method(1), was used in the present study to
conducted PIV image processing. The Hierarchical Recursive PIV method is actual a
hierarchical recursive process of conventional spatial correlation method. The recursive
operation started with a large interrogation window size and search distance, which is as
the same as conventional correlation analysis based PIV image processing methods. By
using the results of former iteration step as the approximate offset values in the next
iteration step, the interrogation window size and search distance were reduced
hierarchically. The conventional correlation method always used 64 by 64 pixel or 32 by
32 interrogation windows, the hierarchical recursive PIV method can reduce the final
interrogation window up to 8 by 8 pixel with spurious vectors being less than 2%.
In order to obtain whole field quantitative concentration distribution in the objective
flow from LIF images, an improved whole-field calibration procedure(2) was conducted
to account for the laser sheet non-uniformity. In order to improve the accuracy level of
the PLIF the measurement results, averaged background substracted from the LIF
images. All the PLIF images were also normalized to account for the laser sheet
intensity variations. A general mapping method(3) was used in the present to get the
spatial correlation between the PIV and PLIF images.
Since the spatial resolution of PIV results is determined by the sizes of the
interrogation window used for correlation operation. The final interogation window size
is 8 by 8 pixel for the present study, so the concentration data were also averaged over 8
by 8 subwindows during the PLIF image processing.
Once the velocity and concentration fields were calculated, it is relatively
straightforward to calculate the various ensemble-averaged velocity ( U ,V ), turbulent
velocity fluctuations ( (u ' u ' ) , (v ' v ' ) ), mean concentration (C), concentration standard
deviation ( c ' c ' ) and the turbulent flux terms ( u ' c ' , v ' c ' ) which is the correlation terms
between the velocity and concentration.
EXPERIMENTAL RESULTS AND DISCUSSIONS
Figure 2 shows a typical pair of the instantaneous PIV and PLIF measurement results.
Since the final interrogation window size is 8 by 8 pixel for PIV image processing, about
50,000 vectors can be got for every instantaneous PIV frame. The velocity vectors shown
in Fig. 2(a) displays only 25% of the PIV velocity vectors. Fig. 2(b) shows the
instantaneous concentration field obtained by PLIF image processing, which is the
simultaneous measurement result of the PIV results shown on Fig. 2(a). The contour
levels given in the figure represent Rhodamine B concentration levels normalized by the
jet source concentration ξ0 =0.3mg/l. It is well known that the shear layer origin form
the exit of the test nozzle is unstable via Kelvin-Helmholtz instability for the circular jet
flow. The instability grows downstream and rolled up into coherent vortex rings. The
vortex ring structures merge as they move downstream and then break down into small
vortex structures. The transition of the jet flow into turbulence occurs when the large
vortex rings break down into small-scale vortices. All these processes can be seen clearly
from the PIV-PLIF simultaneous measurement results shown in Fig. 2.
In the present study, 250 PIV and PLIF image pairs captured simultaneously at the
frame rate of 10Hz were used to calculate the ensemble-averaged values. The ensemble-
averaged values were also normalized with the core jet velocity U0=0.20 m/s and jet
source concentration ξ0=0.3 mg/l. Figure 3 shows the profiles of ensemble-averaged
velocity and mean concentration profiles in the three downstream locations of the
turbulent jet flow. The measurement results of Lemoine et al.(4) by using single point
measurement techniques (LDV and LIF) at 4D downstream of a circular jet flow at the
same Reynolds level as the present case have also been given in the figures. It can be
seen that the present PIV and PLIF simultaneous measurement results agreed with the
measurement results of Lemoine et al. reasonable well.
Figure 4 shows the distributions of various ensemble-averaged terms, which include
ensemble-averaged velocity ( U , V ), ensemble-averaged concentration (C), turbulent
intensity ( (u ' u ' + v ' v ' ) ), concentration standard deviation ( c ' c ' ) and the radial and
axial turbulent flux terms ( u ' c ' , v ' c ' ). From the ensemble-averaged velocity and mean
concentration distributions, it can be seen that there exits a hight speed and high
concentration region in the center of the jet trublent flow, which is called potential core
region. High turbulent intensity and high concentration fluctuation regions exist in the
shear layers between the jet flow and ambinet flows, while in the potiential core region
both turbulent intensity and concentration fluctuation values are low. The pontial core
region extended to Y/D>4.0 downstream, which is consistent with the result of that the
length of potential core region of a conventional circular jet flow ranges about 4D to 6D(5).
Although the ensemble-averaged axial velocity component is much bigger than the radial
velocity component in the near field of the turbulent jet flow, the axial turbulent flux
v ' c ' and radial turbulent flux u ' c ' were found to be almost at the same order from the
present measurement results.
SUMMARY
The development of a high resolution PIV-PLIF combined system, which can achieve
the velocity and concentration simultaneous measurements of fluid flows, was described
in the present paper. The PIV tracer particles and fluorescent dye (Rhodamine B) were
premixed in an object flow and the objective fluid flow was illuminated by a double
pulsed Nd:YAG laser. The LIF light and scattered illuminating laser light were separated
successfully by using two kinds of optical filters, and recorded simultaneously by two
high-resolution CCD cameras. The system was applied to measure the velocity and
concentration distributions in the near field of a circular jet flow simultaneously. The
distributions of the ensemble-averaged velocity and concentration, turbulent
velocity fluctuation, concentration standard deviation and the correlation
terms between the fluctuating velocities and concentration are presented as
the measurement results of the simultaneous PIV-PLIF system.
REFERENCES
1. Hu H. et al. 2000. In Proc. of 9th International Symposium on Flow Visualization, Edinburgh,
Scotland, UK, Aug. 22-25. 2000.
2. Hu H., et al. 2000. In Proc. of 4th JSME-KSME Jointed Thermal Engineering Conference,
Kobe, Japan, Oct. 1-6, 2000.
3. Soloff S. M., Adrian R. J. and Liu Z. C. 1997, Measurement Science and Technology, 8:14411454.
4. Lemoine F., Wolff M. and Lebouche M, 1996. Experiments in Fluids. 20:341-327.
5. Hinze, J. O. 1959, Turbulence, McGraw-Hill Book Company
Laser sheet water tank
low pass optical filter
mixing region
Beam splitter
Double-pulsed Nd:YAG Laser
CCD camera #2
mirror
High pass optical filter for PLIF
Overflow system
A cylindrical
plenum chamber
synchronizer
Test nozzle
pump
jet supply tank
reserve tank
for PIV
CCD camera #1
Flowmeter
Figure 1. Experimental system setup
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concentration
4.5
4
4
3.5
3.5
Y/D
Y/D
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
4.5
0.25 m/s
3
2.5
3
2.5
2
2
1.5
1.5
1
-2
-1
0
1
2
-2
X/D
-1
0
1
2
X/D
a. PIV measurement results
b. simultaneous PLIF measurement results
Figure 2. Typical instantaneous meansurement results of the PIV-PLIF combined system
1.2
1.2
ensemble-averaged axial velocity V
ensemble-averaged concentration, C
1
1
2D
3D
4D
lemoine et al.
0.8
0.6
0.8
2D
3D
4D
lemoine et al.
0.6
0.4
0.4
0.2
0.2
0
0
0
0.5
1
1.5
2
0
0.5
1
1.5
a. ensemble-averaged concentration
ensemble-averaged axial velocity
Figure 3. ensemble-averaged concentration and velocity profiles
2
5
5
4.5
4.5
mean concentration
0.950
0.900
0.850
0.800
0.750
0.700
0.650
0.600
0.550
0.500
0.450
0.400
0.350
0.300
0.250
0.200
0.150
0.100
Y/D
3.5
3
2.5
2
4
3.5
Y/D
4
0.25 m/s
3
2.5
2
1.5
1.5
-2
-1
0
1
2
3
-2
-1
0
X/D
a. mean concentration distribution
concentration
standard deviation
4.5
3.5
3
2.5
2
3
Turbulent intensity
(u'u'+v'v')
1/2
4
0.300
0.280
0.260
0.240
0.220
0.200
0.180
0.160
0.140
0.120
0.100
0.080
0.060
0.040
3.5
3
2.5
2
1.5
-2
2
b. mean velocity distribution
4.5
0.380
0.360
0.340
0.320
0.300
0.280
0.260
0.240
0.220
0.200
0.180
0.160
0.140
0.120
0.100
0.080
0.060
0.040
4
Y/D
5
Y/D
5
1
X/D
1.5
-1
0
1
2
3
-2
-1
0
X/D
1
2
3
X/D
c. concentration standard deviation c'c' distribution
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2
2
d. tubulent intensity (u' +v' )
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4.5
4.5
axial turbulent flux
radial turbulent flux
v'c'
u'c'
4
4
0.030
0.026
0.022
0.018
0.014
0.010
0.006
0.002
-0.002
-0.006
-0.010
-0.014
-0.018
-0.022
-0.026
-0.030
3
2.5
2
3
2.5
2
1.5
-2
0.035
0.033
0.031
0.029
0.027
0.025
0.023
0.021
0.019
0.017
0.015
0.013
0.011
0.009
0.007
0.005
3.5
Y/D
Y/D
3.5
1.5
-1
0
1
X/D
2
3
-2
-1
0
1
2
X/D
e. radial turbulent flux term c'u ' distribution
f. axial turbulent flux term c'v' distribution
Figure 4. Ensemble averaged meansurement results of the PIV-PLIF combined system
3