Experimental investigation of two heated oblique

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, (IJMET)
AND TECHNOLOGY Sep- Dec (2012) © IAEME
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 3, Issue 3, September - December (2012), pp. 669-681
IJMET
© IAEME: www.iaeme.com/ijmet.asp
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©IAEME

EXPERIMENTAL INVESTIGATION OF TWO HEATED OBLIQUE
JETS INTERACTING WITH A TURBULENT FLOW
Tcheukam-Toko D.*1 and Paranthöen P.2
1
Department of Energetic Engineering, University Institute of Technology. P. O. Box
455, Ngaoundere, Cameroon.
2
CNRS UMR 6614 CORIA, University of Rouen. P. O. Box 12 – 76801 Saint-
Etienne du Rouvray, France
* Corresponding author. Email: tcheukam_toko@yahoo.fr

ABSTRACT

The objective of this study is to analyse experimentally the thermal field of two air-
jets inclined at 45° interacting with a turbulent longitudinal flow. The heating of the air-jets
before their entrance simulates the passive scalar. At the outlet, the air-jets generate some
vortexes in the longitudinal flow. The measurement of temperature and fluctuations are
carried out with the help of a hot wire anemometer. The mean temperature fields and
fluctuations are represented in the 0yz plane in different positions on longitudinal axis. The
results show that the mode of the passive scalar dispersion verified previous works carried
out. The temperature fluctuations increase with the passive scalar dispersion as the jets go
away from the source.

KEYWORDS: Jets, thermal field, passive scalar, turbulent flow, temperature fluctuations,
vortex, experiments.

I. INTRODUCTION

Air pollution has become over time a worrying phenomenon in the world. One of the
factors contributing to this atmosphere pollution is the hot gas emitted by heat engines as jets.
To better understand the movement of these jets and heat dispersion in the atmosphere, it is
necessary to study its transport from the moment they are issued until their total dispersion.
Now days, many studies have been done on the dynamic aspect. In preliminary studies made
in the wake of Ahmed body, Gosse [1] showed that the velocity of the longitudinal flow
dominated the jet velocity gradually as one moves away from the source. The jets may also
be issued at an angle for generating vortices in a longitudinal flow. On this subject, Küpper
[2] used two numerical models to explain the control of boundary layer phenomena and heat
transfer at the entrance of the reactors. Tilmann [3] showed in an experimental study the
669

6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
Sep

influence that a discontinuous jet, emitted at a given frequency can have on a turbulent flow. Other
experimental studies have shown that the heat contained in the jets moved in the longitudinal direction
tudies
of the flow. For example those of Kothnur and Clemens [4], which in addition show that the
],
directions of the scalar propagation and the normal shear stress are perpendiculars s.Despite these
numerous studies, there are still gray areas including understanding the phenomena of temperature
ere
fluctuations on the passive scalar dispersion. The aim of our study is to make an experimental
investigation of the thermal field of a turbulent flow interacting with two heated oblique jets. This will
help to understand the influence of temperature fluctuations on the passive scalar dispersion in order
to better explain the phenomenon of air pollution. The design and construction of the model were
of
made in the laboratory. The choice of holes diameter jet emission has been based on the work of Gibb
h n
and Anderson [5], and more recently those of Gosse [1]. The jets’ emissions are inclined by 45
], [ 45°,
based on the work of Bray and Garry [6], this inclination is an optimal position to have good quality
[
jets and eddies in the longitudinal flow. To carry out this study, we first describe the experimental
device, and then, we do an analysis of mean temperature fields and of standard deviation of the t
temperature.

II. MATERIEL AND METHODS
METHOD

In this study, the main flow is the air generated by a blower longitudinal plane type “open
plane,
circuit” which can generate flow velocities (U∞), between 3m.s-1 and 12.5m.s-1. We used hot wire
anemometry as measurement technique.
technique

II.1 Blower type “open circuit”
This blower, built by Delta Lab, is shown in Figure 1. It consists of a motor-driven fan of the
Lab driven
centrifugal type providing a maximum flow rate of 0.32 m3.s-1. The revolutions number of the fan is
viding 0.
regulated by the intermediary of a variable speed transmission supplied with 220 V single single-phase
currents. The air circuit comprises a diffuser located in the rectangular fan discharge. The two gratings
(wire cloth) located downstream of the dust filter to reduce the level of turbulence and homogenize
the flow. In the output of the two-dimensional convergent (section 80x200 mm2), the maximum
two
velocity of the flow is set between 3 m.s-1and 20 m.s-1. The level of turbulence at the nozzle outlet is
in the order of 0.35%.

Figure 1: Blower type “open circuit”

670


The two oblique jets are diverted 45° in a plane perpendicular to the main flow (flow
in the outlet of the nozzle) through circular holes made on a plate fixed to the lower edge of
the outlet nozzle. They have each one a diameter of 5 mm and are separate one of the other
by 40 mm as figure 2a shows it. The emission of pollutants is simulated by injecting hot air
through the two holes at a velocity Uj through a small pipe with 5 mm of diameter under the
plate as shown in Figure 2b. The temperature difference ∆Tref between the jet and the outside
is kept constant at 20°C using a regulated power supply. The thermostat of the heating system
is connected to the thermocouple control chamber. This small temperature difference avoids
effects gravitate. The velocity of the heated flow (Uj), is measured by a loss of load
connected to a micro manometer Furness Control. This velocity is adjustable between 1 and
10 m.s-1 as shown in figure 3.The origin 0 of the orthogonal axe (0x, 0y, 0z) is located
equidistant from the two holes i.e, 20 mm of each axis. The two holes are symmetrical
relative to the 0x axis oriented in the direction of the main flow. 0y axis is vertical and the 0z
axis is perpendicular to the main flow.

Figure 2: Plate; a) Front view; b) Top view Figure 3: the device of injection of the hot air

The measured variable in this study is the temperature difference between the heated
zones and upstream fluid. In this study, the sign "+" indicates a normalized quantity. Lengths
are normalized by the distance between the hole and the main axis H equal to 20 mm, and the
temperature difference is normalized by the initial temperature difference ∆Tref. Molecular
effects are negligible compared to the turbulence, the report ∆T/∆Tref can be likened to a
concentration c, will vary between 1 and 0 emission to infinity. For convenience, the time
average and standard deviation of a quantity X are denoted respectively <X> and <X'2>1/2.
The outputs of the two jets heated are located respectively at the point S of coordinates (X+ =
0, Y+ = 0, Z+ = -1), and S 'of coordinates (X+ = 0, Y+ = 0, Z+ = 1).

II.2 Hot wire anemometry
The Measure of a velocity flow using hot wire anemometry is based on convective
heat exchange between the hot wire and the flow. This exchange is used to connect the wire
temperature to Nusselt number (Nu) which is a function of the flow velocity and the current
power I shown by the equation (1). The figure 4 below, illustrates well this principle of
convective exchange. The detail is clear in Paranthoën and Lecordier [7], and Rosset, and al
[8].

671


Tw = Tg +
( ( ))
R 0 1 + α Tg − T0 I²
where, Nu =
hd
. (1)
Nuπlλ g − αR 0 I² λg
The hot wire anemometer operates at constant temperature. In this case, when the
flow velocity varies, measuring the current I needed to keep the temperature Tw of the wire,
constant. This technique provides a frequency response of approximately100 kHz.
The electrode used is a set TSI, consisting of a sensor to a wire, a processor and an
IFA conversion board 12-bit analog voltage, installed in a PC with high memory capacity and
storage. Probes conducted in the laboratory are made with platinum-rhodium10%, with 3 µm
of diameter. A schematic of the probe used is presented in figure 5.
The response of the wire as a function of the velocity is not linear. Calibration of the
hot wire placed in the outlet section of the jet; is performed before each series of
measurements by varying the velocity of the flow. An example of a calibration curve is
shown in figure 6. The experimental points are then approximated by a polynomial of
ordernor with a selected interpolation function type "Cubic Spline". The temperature of the
flow is measured by a thermocouple type K and recorded. If there are any changes in the
temperature of the flow, a correction can thus be applied to the measured voltage.

L = lengthof the wire.
D =diameter of the wire
I = electrical current
Rw = operating resistance of the hot wire at Tw
Tw = Temperature of the hot wire.
U = Flow velocity
Tg = Temperature of the surrounding air
Figure 4: Schematic of hot wire
Table 4: Legend of figure 4

2
1.9
1.8
1.7
tension (V)

1.6
1.5
1.4
1.3
1.2
1.1
1
0 5 10 15 20 25
Figure 5: Diagram of the hot wire probe used vitesse (m /s)

Figure 6: Example of a calibration curve of a
hot wire: voltage in function of the velocity

II.3 Temperature measurement
The instantaneous signal T(t) of temperature can be decomposed as:
T(t) = <T> + T’(t) (2)
<T> is the temporal mean value and T'(t) is the temperature fluctuation. The signal is
characterized by a mean value <T>, and centered moments that allow access to the standard

672


deviation <T'2>1/2. In our case, each mean time is calculated on a sample of more than
200,000 points.
1 N
Mean temperature: < T >= ∑ Ti (3)
N i =1
1 N
Variance: < T '2 >= ∑ (Ti − < T >) 2 (4)
N i =1
In the experiments of dispersion downstream from the linear sources or point sources,
the variations in temperature which one must measure quickly become relatively weak. The
temperature signal is thus influenced by the background noise as the distance from the
source. This requires making corrections to background noise to accurately measure the
actual signal. Assuming that the instantaneous value of the temperature can be written in the
following form:
Tmes (t) = <T>V + T’V (t) + T'BF (t) (5)
The subscripts “mes”, "V" and "BF" correspond respectively to the measured values, true
values and background noise values. To make the corrections of noise on the variance, we
used the following equation:
Variance: < T '2 > V =< T '2 > mes − < T '2 > BF (6)

III. RESULTS AND DISCUSSION

We conducted several series of temperature measurements by choosing a single
longitudinal flow velocity Ui = 5 m/s for different jets velocities Uj, equal to 5 m/s, 10 m/s
and 20 m/s), corresponding to the Reynolds number (Re = Ud/ν), of 1200, 2400 and 4800. To
show more details, we performed measurements in the plane (Y+, Z+) with a very small mesh.
On the Z+ axis, the scan was between -2.5 to +2.5 values with 1/20 of step of measuring. On
the Y+ axis, the scan was between 0 to 1.5 values with 1/20 of step of measuring. That makes
a total of 3,000 points of space measurements.

III.1 Means temperatures
The figures 7a, 7b and 7c below represent the iso-values of mean temperature at the
positions X+ = 0.5; X+ = 2.5 and X+ = 5; for a jets velocity of 5 m/s (in this case, the jets
velocities are equal to the longitudinal flow velocity, (Uj equal to Ui.). These figures show
that the two jets are symmetric with respect to the axes 0X+and 0Y+, and even when one is in
a remote position (X+ = 5). We observe a low dispersion of the passive scalar in this position
and the area of the intermediate temperature (<T> = 0.099), becomes predominant. The two
jets are still largely dominated by the longitudinal flow that prevents the plate off. The area
where the temperature is high (<T> = 0.3) remains sticking to the plate along the longitudinal
axis 0X+.
The figures 8a,8b, 8c and 8d below represent the iso-values of mean temperature in
the positions X+= 0.5; X+ = 1, X+= 2.5 and X+= 5, when the jets have a Reynolds number of
2400. We note that the two jets take off from the plate upon release (X+= 0.5), and reach the
coast Y+ = 1 from the position X+= 2.5. The size of the hottest zone (<T> = 0.3), decreases as
the distance along the longitudinal axis. It disappears almost completely at the position X+ =
5, and the intermediate zone (<T> = 0.099), becomes very dominant and invades the entire
area near the plate (Y+ =0). Coast Y+ = 1 appears as the maximum height reached by the
hottest zone of the jets. The two jets are no longer symmetrical relative to the axes 0X+and
0Y+ from the position X+= 1, also considered as the position where the scalar begins to

673


undergo a dispersion. This is very important when the jets reach the position X+ = 5, in the
area where Y+ ≤ 1, the temperature is greater than zero.
The figures 9a, 9b, 9c and 9d below represent the iso-values of mean temperature in
different positions of the plane (Y+, Z+), for jets with a Reynolds number of 4800. We note
that the two jets are less influenced by the longitudinal flow. They quickly take off the plate
at the position X+ = 0.5 and cross the coast Y+ = 1.5 at the position X+ = 5. The size of the
hottest zone (<T>= 0.33), decreases significantly from the position X+ = 0.5. It disappears
completely in a jet and still a bit in the other, specifically one that is close to the axis 0X+.
This shows that the scalar disperses less rapidly than in the previous case (Re = 2400). The
size of the intermediate zone (<T> = 0.099), becomes dominant and the asymmetry of the
two jets with respect to axes 0X+ and 0Y+ is even more significant.
In these three sets of measures, we note that in the case where the jets could be less
influenced by the longitudinal flow (Re= 4800), there are quick release streams of the plate
but the scalar disperses less. This is obvious for all three positions because at X+ = 5, the
temperature is <T> = 0 (dark blue) on the wall of the plate, and different from zero in the
region close to the wall for other cases Re = 1200 and Re = 2400. This heat dispersion on the
plate is translated by the shape of the isotherms which spread much on the plate.

a)
TEMPERATURE
0.357274
0.335275
0.313276
0.291277
0.269278
0.247279
0.225279
0.20328
0.5 0.181281
Y+

0.159282
0.137283
0.115284
0.0932846
0.0712855
0.0492863

0
-2 -1 0 1 2
Z+

b)
TEMPERATURE
0.267911
0.249998
0.232085
0.214172
0.196258
0.178345
0.160432
0.142519
0.5 0.124605
Y+

0.106692
0.0887788
0.0708656
0.0529523
0.035039
0.0171258

0
-2 -1 0 1 2
Z+

c)
TEMPERATURE
0.14093
0.13416
0.12739
0.120619
0.113849
0.107079
0.100309
0.0935391
0.5 0.086769
Y+

0.079999
0.0732289
0.0664588
0.0596887
0.0529186
0.0461485

0
-2 -1 0 1 2
Z+

Figure 7:Iso-values of mean temperature fields<T>in the plane (Y+, Z+),Re= 1200
a): X+= 0.5;b): X+= 1; c): X+ = 5

674


a)
TEMPERATURE
0.31228
0.292557
0.272835
0.253112
0.233389
0.213667
0.193944
0.174221
0.154499

Y+
0.5 0.134776
0.115053
0.0953308
0.0756082
0.0558855
0.0361629

0
-2 -1 0 1 2
Z+

b)
1
TEMPERATURE
0.244115
0.227533
0.210951
0.194368
0.177786
0.161204
0.144621
0.128039
0.111457

Y+
0.0948743
0.5 0.078292
0.0617097
0.0451273
0.028545
0.0119627

0
-2 -1 0 1 2
Z+

c)

TEMPERATURE
0.15801
0.147178
1 0.136345
0.125513
0.11468
0.103848
0.0930151
0.0821826
0.07135
Y+

0.0605175
0.0496849
0.0388524
0.5 0.0280198
0.0171873
0.00635474

0
-2 -1 0 1 2
Z+

d)
1.5

TEMPERATURE
0.1004
0.0929762
0.0855525
0.0781287
0.0707049
1 0.0632811
0.0558573
0.0484335
0.0410097
Y+

0.0335859
0.0261621
0.0187384
0.0113146
0.5 0.00389077
-0.00353301

0
-2 -1 0 1 2
Z+

Figure 8:Iso-values of mean temperature fields<T>in the plane (Y+, Z+),Re= 2400
a): X+= 0.5;b): X+= 1; c): X+ = 2.5;d): X+ = 5

675


a)
1.5

TE M PE R A T U R E
0 .295613
0 .275175
0 .254737
0 .234299
0 .213861
1 0 .193424
0 .172986
0 .152548
0 .13211

Y+
0 .111672
0 .0912341
0 .0707962
0 .0503583
0.5 0 .0299204
0 .00948254

0
-2 -1 0 1 2
Z+

b)
1.5

TE M PE R A T U R E
0 .22666
0 .210599
0 .194539
0 .178478
0 .162417
1 0 .146356
0 .130295
0 .114234
0 .0981732
Y+ 0 .0821123
0 .0660514
0 .0499906
0 .0339297
0.5 0 .0178688
0 .00180789

0
-2 -1 0 1 2
Z+

c)
1 .5

TEMPERATUR E
0 .159154
0 .14855
0 .137945
0 .12734
0 .116735
1 0 .106131
0 .0955258
0 .084921
0 .0743163
Y+

0 .0637115
0 .0531067
0 .0425019
0 .0318971
0 .5 0 .0212924
0 .0106876

0
-2 -1 0 1 2
Z+

d)
1.5

TEMPERATURE
0 .11203
0 .104573
0 .097117
0 .0896605
0 .0822041
1 0 .0747476
0 .0672912
0 .0598347
0 .0523783
Y+

0 .0449218
0 .0374654
0 .0300089
0 .0225524
0.5 0 .015096
0 .00763954

0
-2 -1 0 1 2
Z+

Figure 9: Iso-values of mean temperature fields<T>in the plane (Y+, Z+),Re= 4800.
a): X+= 0.5;b): X+= 1; c): X+ = 2.5;d): X+ = 5
III.2 Standard deviation of means temperature
We obtain the temperature fluctuations shown in the previous paragraph that we
represent through the standard deviations.
The figures 10a, 10b, and 10c below represent the iso-values of the standard deviation
of mean temperatures in different positions of the plane (Y+, Z+), for a Reynolds number of
1200. We note that the symmetry of the two jets with respect to axes 0X+ and 0Y+ is
confirmed. The standard deviation of the mean temperature decreases when the jets move

676


away along the longitudinal axis 0X+. At the position X+= 0.5, this iso-value is 0.04 in the
hottest zone and it become 0.01 at the position X+ = 5. The influence of longitudinal flow on
the two jets is very important.

The figures 11a, 11b, 11c and 11d below represent these standard deviations in
different positions of the plane (Y+, Z+) for a Reynolds number of 2400. The decrease of the
standard deviation with distance along the longitudinal axis is confirmed. In the hottest zone,
it is from 0.06 at X+ = 0.5, and 0.02 at X+ = 5. The asymmetry between the two jets is
observed from the position X+ = 1.

a)

EAT YE
C R -T P
0.0494505
0.0461963
0.0429421
0.0396879
0.0364337
0.0331795
0.0299252
0.026671
0.5 0.0234168
Y+

0.0201626
0.0169084
0.0136542
0.0104
0.00714577
0.00389156

0
-2 -1 0 1 2
Z+

b)

EAT YE
C R -T P
0.0358285
0.0334971
0.0311658
0.0288344
0.026503
0.0241716
0.0218403
0.0195089
0.5 0.0171775
Y+

0.0148462
0.0125148
0.0101834
0.00785206
0.00552069
0.00318932

0
-2 -1 0 1 2
Z+

c)

E T-T
CAR YPE
0.018631
0.0174407
0.0162505
0.0150602
0.0138699
0.0126796
0.0114894
0.0102991
0.5 0.00910883
Y+

0.00791856
0.00672829
0.00553802
0.00434775
0.00315748
0.00196721

0
-2 -1 0 1 2
Z+

Figure 10: Standard deviation of mean temperature<T'2>1/2in the plane (Y+, Z+). Re= 1200.
a): X+= 0.5; b): X+= 1; c): X+ = 5

677


a)

EC ART-TYPE
0.0646835
0.0604049
0.0561262
0.0518476
0.047569
0.0432903
0.0390117
0.0347331
0.0304544

Y+
0.5 0.0261758
0.0218972
0.0176185
0.0133399
0.00906128
0.00478265

0
-2 -1 0 1 2
Z+

b)
1
ECART-TYPE
0.0518896
0.0484646
0.0450396
0.0416146
0.0381896
0.0347647
0.0313397
0.0279147
0.0244897

Y+
0.0210647
0.5 0.0176398
0.0142148
0.0107898
0.00736482
0.00393984

0
-2 -1 0 1 2
Z+

c)

ECART-TYPE
0.0336098
1 0.0314054
0.0292009
0.0269965
0.0247921
0.0225876
0.0203832
0.0181788
0.0159743
Y+

0.0137699
0.0115655
0.5 0.00936104
0.0071566
0.00495217
0.00274773

0
-2 -1 0 1 2
Z+

d)
1.5

ECART-TYPE
0.0233372
0.0218155
0.0202938
0.0187721
0.0172504
1 0.0157287
0.014207
0.0126853
0.0111636
Y+

0.00964191
0.00812021
0.00659851
0.00507681
0.5 0.0035551
0.0020334

0
-2 -1 0 1 2
Z+

Figure 11: Standard deviation of mean temperature<T'2>1/2in the plane (Y+, Z+). Re= 2400.
a): X+= 0.5; b): X+= 1; c): X+ = 2.5; d) X+ = 5.

The figures 12a, 12b, 12c and 12d below represent these standard deviations in the
previous positions of the plane (Y+, Z+) for a Reynolds number of 4800. In the hottest zone,
the standard deviation increases when the two jets move along the longitudinal axis.
In general, we note that highest standard deviation of the mean temperature
corresponds to the values of Reynolds number 2400. We saw in the previous section that this
case of Re = 2400, was one where the dispersion of passive scalar was perfect.

678


a)
1 .5

E C A R T -T Y P E
0 .0 3 6 6 7 7 1
0 .0 3 4 2 5 2 2
0 .0 3 1 8 2 7 4
0 .0 2 9 4 0 2 5
0 .0 2 6 9 7 7 7
1 0 .0 2 4 5 5 2 8
0 .0 2 2 1 2 8
0 .0 1 9 7 0 3 2
0 .0 1 7 2 7 8 3

Y+
0 .0 1 4 8 5 3 5
0 .0 1 2 4 2 8 6
0 .0 1 0 0 0 3 8
0 .0 0 7 5 7 8 9 6
0 .5 0 .0 0 5 1 5 4 1 2
0 .0 0 2 7 2 9 2 8

0
-2 -1 0 1 2
Z+

b)
1 .5

E C A R T -T Y P E
0 .0 2 9 6 0 2 7
0 .0 2 7 6 9 2 1
0 .0 2 5 7 8 1 4
0 .0 2 3 8 7 0 8
0 .0 2 1 9 6 0 2
1 0 .0 2 0 0 4 9 6
0 .0 1 8 1 3 9
0 .0 1 6 2 2 8 4
0 .0 1 4 3 1 7 8

Y+
0 .0 1 2 4 0 7 2
0 .0 1 0 4 9 6 6
0 .0 0 8 5 8 5 9 9
0 .0 0 6 6 7 5 3 8
0 .5 0 .0 0 4 7 6 4 7 8
0 .0 0 2 8 5 4 1 7

0
-2 -1 0 1 2
Z+

c)
1 .5

E C A R T -T Y P E
0 .0 2 0 0 0 2 2
0 .0 1 8 6 8 2 8
0 .0 1 7 3 6 3 5
0 .0 1 6 0 4 4 1
0 .0 1 4 7 2 4 7
1 0 .0 1 3 4 0 5 3
0 .0 1 2 0 8 5 9
0 .0 1 0 7 6 6 5
0 .0 0 9 4 4 7 1 7
Y+

0 .0 0 8 1 2 7 7 8
0 .0 0 6 8 0 8 4
0 .0 0 5 4 8 9 0 2
0 .0 0 4 1 6 9 6 4
0 .5 0 .0 0 2 8 5 0 2 6
0 .0 0 1 5 3 0 8 8

0
-2 -1 0 1 2
Z+

d)
1 .5

E C A R T -T Y P E
0 .0 1 4 0 8 0 9
0 .0 1 3 1 7 8 2
0 .0 1 2 2 7 5 4
0 .0 1 1 3 7 2 7
0 .0 1 0 4 7
1 0 .0 0 9 5 6 7 2 3
0 .0 0 8 6 6 4 4 9
0 .0 0 7 7 6 1 7 6
0 .0 0 6 8 5 9 0 2
Y+

0 .0 0 5 9 5 6 2 9
0 .0 0 5 0 5 3 5 5
0 .0 0 4 1 5 0 8 2
0 .0 0 3 2 4 8 0 8
0 .5 0 .0 0 2 3 4 5 3 5
0 .0 0 1 4 4 2 6 2

0
-2 -1 0 1 2
Z+

Figure 12: Standard deviation of mean temperature<T' > in the plane (Y+, Z+). Re= 4800.
2 1/2

a): X+= 0.5;b): X+= 1;c): X+ = 2.5; d) X+ = 5
IV. CONCLUSIONS

The interaction between a longitudinal flow and two jets preheated has a great
influence on the passive scalar dispersion. In view of the figures shown in the previous
sections, we can say that when the two jets are issued, the scalar is transported directly
downstream from a straight line by gradually dispersing. This has already been highlighted
by Gosse [1], in the wake of Ahmed body. This dispersion is best done in the case where the
jets are less influenced by the longitudinal flow. To further explore this issue, a study of the
dynamic range must be made to understand the influence of the vortex on the dispersion of
passive scalar in the turbulent flow.

ACKNOWLEDGEMENT

The authors acknowledge the CORIA UMR 6614 CNRS University of Rouen-France,
and The University Institute of Technology of Ngaoundere, Cameroon.

679


REFERENCES

[1] K. Gosse. Etude de la dissipation d’un scalaire passif en aval d’un corps d’Ahmed. Ph. D.
Thesis. University of Rouen, France, 2006.
[2] C. Kupper and F. S. Henry, Numerical simulation of flow in a circular duct fitted with air-
jet vortex generators, Int. J. Numer. Meth. Fluids, 38: 919 – 943, 2002.
[3] C. P. Tilmann, K. J. Langan, J. G. Betterton and M. J. Wilson, Characterization of pulsed
vortex generator jets for active flow control. Symposium on “Active Control Technology for
enhanced performance operational capabilities of military aircraft: Land vehicles and sea
vehicles”. RTO MP-051, 8 – 11. Germany, 2000.
[4] P. S. Kothnur and N. T. Clemens, Effects of unsteady strain rate on scalar dissipation
structures in turbulent planar jets. Physics of fluid, 17, 2005.
[5] J. Gibb and B. H. Anderson, Vortex flow control applied to aircraft intake ducts. CEAS
Europeans Forum on high lift & separation control, Bath, UK, 1995.
[6] T. P. Bray and K. P. Garry, Optimisation of jet vortex generators with respect to system
design parameters. The Aeronautical Journal, 1999.
[7] P. Paranthoën and J. C. Lecordier, Mesure de température dans les écoulements. Revue
Générale de la Thermique, 34, pp. 286 – 308. Elsevier, Paris, 1996.
[8] L. Rosset, P. Paranthoën, J. C. Lecordier and M. Gonzalez, Anisotropy of a thermal field
at dissipative scales in the case of small-case injection. Phys. Fluids., 13, 3729 – 3737, 2001.
[9] Kavitha T, Rajendran A, Durairajan A and Shanmugam A, “Heat Transfer Enhancement
Using Nano Fluids And Innovative Methods - An Overview"International Journal of
Mechanical Engineering & Technology (IJMET), Volume3, Issue2, 2012, pp. 769 - 782,
Published by IAEME.
[10] Dr P.Ravinder Reddy, Dr K.Srihari and Dr S. Raji Reddy “Combined Heat And Mass
Transfer In Mhd Three-Dimensional Porous Flow With Periodic Permeability & Heat
Absorption” International Journal of Mechanical Engineering & Technology (IJMET),
Volume3, Issue2, 2012, pp. 573 - 593, Published by IAEME.

NOMENCLATURE

Small letters
x = longitudinal coordinate (m)
y = vertical coordinate (m)
z = transversal coordinate (m)
d = diameter of the holes on the plate (m)

Capital letters
H distance between one of the two holds from the principal axe (m)
∆Tréf Temperature difference between hot jet and the exterior (K)
T’ Temperature fluctuations (K)
Rw Hot wire resistance (Ω)
Pui Electrical power supplied (Watt)
Ui Flow velocity at the outlet of the nozzle (m.s-1)
Uj Jet exit velocity (m.s-1)
0x longitudinal axis
0y vertical axis

680


0z transversal axis
S The location point of the two jets sources

Greeksymbols
ν Kinetic viscosity of air (m2.s-1)
ρ Volume mass (Kg.m-3)
λ Thermal conductivity (J.m-2)

No dimensional numbers
Re Reynolds number
Prt Turbulent Prandtl number
Nu Nusselt number

Exponents, indices and specials characters
+ Normalized value (H for lengths) and (∆Tréf for temperatures)
<T> Mean temperature T
<X> Means time of a quantity X
2 1/2
<X' > Standard deviation of a quantity X
<X'2> Variance of a quantity X

681

Experimental investigation of two heated oblique

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