M.S research

9
INVESTIGATION OF THREE PARALLEL
JETS IMPINGING ON A VERTICAL PLATE
Nawaf Mohammed Al-Fadul
FACULTY OF ENGINEERING
KING ABDULAZIZ UNIVERSITY, JEDDAH
SAFAR 1424H - APRIL 2003G

11
By
A thesis submitted in partial fulfillment of the requirements for the degree of
Master of Science in Mechanical Engineering / Mechanical Power.
FACULTY OF ENGINEERING
KING ABDULAZIZ UNIVERSITY
JEDDAH, SAUDI ARABIA
SAFAR 1424H –APRIL 2003G

12
By
We certify that We have read this thesis and that in our opinion is fully adequate
in scope and quality as a thesis for the degree of Master of Science.
Thesis Supervisors:
-------------------------------------------------
Dr. Mohammed Hussain Albeirutty
--------------------------------------
Prof. Jafer Abdulrahman Sabbagh

13
By
Nawaf Mohammed Al-fadul
This thesis has been approved and accepted in partial fulfillment of the
requirements for the degree of Master of Science
Examiners:
--------------------------------------------
Dr. Mohammed H. Albeirutty , Examiner / Supervisor
--------------------------------------------
Prof. Jafer A. Sabbagh , Examiner /Co-supervisor
----------------------------------------------------------
Dr. Ibrahim E. Megahed , Examiner
----------------------------------------------------------
Dr. Abdulhaiy M. Radhwan , Examiner

14
ACKNOWLEDGEMENT
First I would like to express my gratitude to King Abdulaziz City of Sciences and
Technology (KACST) for their support and funding of this research work.
Also I would like to express my thanks to both of my advisors Professor. Jafer Sabbagh
and Dr. Mohammed Al-Beirutty for their great and continuous overall supervision in
this research until it reached the final required form.
My thanks also is extended to the technical and workshop staff members of thermal
engineering department for their great help and assistance during the manufacturing of
the experimental setup parts.

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ABSTRACT
This thesis depicts an experimental study of the flow field characteristics
of three parallel two-dimensional jets impinging on a normal plate as the
case of VTOL aircraft operating near the ground.
Throughout the course of this work, the flow field characteristics of two
free jets are studied. The results are compared to previous similar studies
in the literature .The results are also compared to that of three free jets
arrangement. The flow field of three impinging parallel jets colliding on a
vertical plate is also investigated. In addition the effect of changing some
parameters such as the jets velocity strength and the distance between the
jets exit plane and the vertical impinging plate is studied.
The measurements of the resultant flow field for free and impinging jets
were conducted using hot-wire probes technique, this included extensive
measurements of the turbulent structure of flow field. Flow visualizations
results which reveal the flow field shape were also obtained using oil chalk
mixture method .All pressure readings on the ground and the vertical
impinging plate were measured using pressure taps connected to an
electronic transducer.
The overall impinging measurements show that in the case of equal
strength impinging jets, the middle jet interact with the interior wall jets
formed by the two outside jet after impinging and lose its strength. In
unequal jets case, the strong middle jet attracts the two weaker side jets
and act as a single jet after impingement. The result shows also that if two
adjacent strong jets interact with one weaker side jet the weaker side jet is
attracted to the middle strong jet and lose its strength, the final velocity
profile becomes similar to two impinging jets.

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TABLE OF CONTENTS
ACKNOWLEDGEMENT……….……………………….……….…….…..……......v
ABSTRACT...……………………………..………………..……………..…………vi
TABLE OF CONTENTS...…………………..………………..…………..……..…..viii
LIST OF TABLES …………………………………………………………………. .x
LIST OF FIGURES...……………………………………..…………………....….....xii
LIST OF SYMBOLS ….…………….…………………..……………..…..….……..xv
CHAPTER I INTRODUCTION AND LITERATURE REVIEW ………………
1
1.1 Introduction ……………………………………………………………..
1
1.2 literature review …………………………………………………………
2
1.3 Research objectives …………………………………………………......
7
CHAPTER II EXPERIMENTAL SETUP ………………………………………
9
2.1 Setup and alignment …………………………………………………….. 9
2.2 Instrumentations ………………………………………………………..
15
2.2.1 Single normal wire probe …………………………………..
16
2.2.2 Triple-sensor gold-plated wire probe ……………………….
17
2.2.3 Data Acquisition …………………………………………….
18
2.3 Calibration of hot-wires ………………………………………………..
19
CHAPTER III MEASUREMENTS AND FLOW VISUALIZATION ……......30
3.1 Symmetry Check ………………………………………………………. 30
vii

17
3.2 Comparison of Single and Triple wire measurements ………………… 32
3.3 Two parallel free jets measurements ………………………………….. 34
3.4 Three parallel free jets measurements ………………………………… 36
3.5 Three parallel impinging jets measurements ………………………….. 37
3.6 Flow Visualization Technique ……………………………………….. .
39
CHAPTER IV DISCUSSION OF RESULTS …………………………………..
40
4.1 Free jet measurements ………………………………………………….
40
4.1.1 Interaction of two free parallel jets …………………………
40
4.1.2 Interaction of three free parallel jets ………………………..
41
4.1.3 Variations of momentum in three parallel jets ……………..
45
4.1.4 Comparison between free jets arrangement results ……......
47
4.2 Impinging jets results …………………………………………………. 50
4.2.1 Single impinging jet ………………………………………..
51
4.2.2 Three parallel impinging jets ………………………………..
51
CHAPTER V CONCLUSIONS AND RECOMMENDATIONS ………………
77
5.1 Conclusion ……………………………………………………………...
77
5.2 Recommendations ………………………………………………………
78
REFERENCES …………………………………………………………………….80
APPENDIX – I TABULATED RESULTS ……………………………………...83
APPENDIX – II COMPUTER PROGRAM. ……………………………………
105

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LIST OF TABLES
TABLE
PAGE
I.1 summery of all vertical plate positions, measurement wire distances
and the type of wire used in the measurements…………………………….. 85
I.2 Mean velocity components and fluctuations results of three parallel
free jets at x/tp=30……………………………..………………………..…..86
free jets at x/tp=50……………………………………………………….… 87
free jets at x/tp=80………………………………………………………… 88
free jets at x/tp=140…………………………………………………..……. 89
impinging jets at H=10cm , x=5cm (x/tp=10)…..………………………... 90
impinging jets at H=20cm , x=5cm (x/tp=10)……………………………. 91
impinging jets at H=20cm , x=10cm (x/tp=20)…………………………… 92
I.9 Mean velocity components and fluctuations results of three paralle
impinging jets at H=30cm , x=10cm (x/tp=20). …..……………………… 93
impinging jets at H=30cm , x=20cm x/tp=40) 94
I.11 Mean velocity components and fluctuations results of three
parallel impinging jets at H=45cm , x=23cm (x/tp=46)………………..… 95
parallel impinging jets at H=45cm , x=24cm (x/tp=48)………………… 96
parallel impinging jets at H=45cm , x=28cm (x/tp=56)……………………97
parallel impinging jets at H=45cm , x=34cm (x/tp=68)…………………… 98
parallel impinging jets at H=45cm , x=40cm (x/tp=80)……………………. 99
I.16 Axial mean velocity and fluctuation results o f three unequal
(Uo1=Uo2=2Uo3) parallel impinging jets at H=45cm, x=40cm 100
I.17 Axial mean velocity and fluctuation results o f three unequal
(Uo1=Uo3=.5Uo2) parallel impinging jets at H=45cm, x=40cm 101
I.18 Upstream flow pressure distributions results for three parallel
Impinging jets at different impinging plate distances . 102
I.19 Upstream flow pressure distributions results for three parallel unequal
impinging jets at H=45 cm. 103
I.20 Ground plane static pressure distributions results for three parallel
equal and unequal impinging jets at H=45 cm and x=4, 28 cm. 104x

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LIST OF FIGURES
Figure Page
2.1 Test rig schematic diagram 9
2.2 Tope views of the old and the modified jet nozzles........................................... 10
2.3 Side view of jets blocks and vertical impinging plate ……………………... ... 11
2.4 Traverse mechanism side view 11
2.5 Air blowers feeding the three jets . 12
2.6 Side view of jets blocks 12
2.7 Dynamic flow board for data acquisition system 13
2.8 Traverse mechanism components 14
2.9 Pressure electronic manometer. 15
2.10 Single wire probe (Miniature wire type provided by Dantec Dynamic
site www.dantecdynamics.com) 16
2.11 Triple wire probe (provided by Dantec Dynamic
site www.dantecdynamics.com). ..17
2.12 Constant Temperature Anemometer layout diagram (by Dantec Dynamic
site www.dantecdynamics.com......................................................... 19
2.13 Velocity components vectors in the laboratory coordinates............................. 20
2.14 Velocity components vectors in the wire coordinates ....................................... 21
2.15 Single sensor robe.............................................................................................. 23
2.16 Triple sensor probe ............................................................................................ 24
2.17 Side view and front view photos of the round jet….......................................... 28
2.18 Calibration curves for (a) single and (b) triple wire probes 29
3.1 Velocity profiles to check jet (1) symmetry 31
3.2 Velocity profiles to check jet (2) symmetry . 31
3.3 Velocity profiles to check jet (3) symmetry . 31
3.4 Comparison of jets symmetry check between current and pervious
studies 32
3.5 Velocity profiles using single and triple wire measurements for a single
free jet at L=50 cm… 33
3.6 Comparison of Axial velocity profile at x/tp=20 between current and
pervious studies 34
3.7 Axial mean velocity profiles of upstream merging region of the two
free parallel jets. 35
3.8 Axial turbulence intensity profiles for double jets arrangement 35
3.9 Axial mean velocity profiles of three free parallel jets. 36
3.10 Schematic diagram of the flow field of three impinging jets 37
4.1 Variations of maximum velocity along the centerline of each
jet with axial distance 43
4.2 Trajectory of the central streamline of each of the three jets. 44
4.3 Axial turbulence intensity profiles in the merging region of three free
parallel jets 44
4.4 lateral turbulence profiles of upstream merging region of three free
parallel jets 45
4.5 Shear stress profiles in the merging region of the three free parallel jets 45
4.6 Variations of momentum of upstream merging region of three free
parallel jets. 47
4.7 Variations of flow momentum along the centerline of each jet with
axial distance. 48
xii

20
4.8 Velocity profiles at x/tp=20 for double and triple jets arrangements 49
4.9 Velocity profiles at x/tp=50 for double and triple jets arrangements . 49
4.10 Axial turbulence intensity profiles at x/tp=50 for double and triple
jets arrangements . 50
4.11 Growth of jet width with downstream distance for single , double
and triple jets arrangements . 51
4.12 Flow visualization of single impinging jet at H=45 cm 52
4.13 Flow visualizations pattern for three equal impinging jets at different
plate distances. 53
4.14 Flow visualizations pattern for two equal impinging jets at different
plate distances [7]. 54
4.15 Pressure distribution across the impinging vertical plate at different
distances from the jets exit 55
4.16 Flow visualization of three impinging jets at H=10 cm.. 56
4.17a Axial and lateral velocity profiles for three equal impinging jets at
x/tp =10 and H=10 cm 56
4.16b Axial and lateral velocity profiles for three equal impinging jets at
x/tp =10 and H=10 cm (corrected on the basis of Fig.4.16) 57
4.18 Axial turbulence intensity profile for three equal impinging jets at
x/tp =10 and H=10 cm 57
4.19 Flow visualization of three impinging jets at H=20 cm 58
4.20a Axial velocity profiles for three equal impinging jets at x/tp =10
and H=20 cm 59
4.20b Axial velocity profiles for three equal impinging jets at x/tp =10
and H=20 cm (corrected on the basis of Fig.(4.19)…....................................... 59
4.21a Lateral velocity profiles for three equal impinging jets at x/tp=20, 40
and H=20 cm 60
4.21b Lateral velocity profiles for three equal impinging jets at x/tp=20, 40
and H=20 cm (corrected on the basis of Fig.4.19) 60
4.22 Axial intensity profiles for three equal impinging jets at x/tp =10,20
and H=20 cm 61
4.24a Axial velocity profiles for three equal impinging jets at x/tp=20, 40
and H=30 cm 62
4.24b Axial velocity profiles for three equal impinging jets at x/tp=20, 40
4.25a Lateral velocity profiles for three equal impinging jets at x/tp =20, 40
and H=30 cm. 63
4.25b Lateral velocity profiles for three equal impinging jets at x/tp =20, 40
4.26 Axial turbulence intensity profiles for three equal impinging jets at
x/tp =20, 40 and H=30 cm 64
4.28 Static pressure distribution across the ground horizontal plate for
three equal strength jets at H=45 cm……………………………………….... 66
4.29a Flow map for the right side of the visualization pattern of three
impinging jets at H=45 cm……..……………….....................…………… .... 66
4.29b Velocity vectors at the measuriments locations of three impinging
jets at H=45 …….………………………………………………………….…. 67
4.30a Axial velocity profiles for three equal impinging jets at x/tp =46
48, 56, 68, 80 and H=45 cm…………………………………………….….… 68
4.30b Axial velocity profiles for three equal impinging jets at x/tp =46
48, 56, 68, 80 and H=45 cm (corrected on the basis of Fig.4.27)………..…... 68
4.31 Lateral velocity profiles for three equal impinging jets
at H=45 cm………………………….……………….………………..…..…… 69
4.32 Axial turbulence intensity profiles for three equal impinging jets
at x/tp =46, 48, 56, 68, 80 and H=45cm ……………………..………....……...69
4.33 Pressure distribution across the impinging vertical plate for
three equal and unequal jets at H=45 cm…………………...…..…………..... 70
xiii

21
4.34 Static pressure distribution across the ground horizontal plate three
unequalstrength jets (Uo1=Uo3=50%Uo2) at H=45 cm……………..……71
4.35 Static pressure distribution across the ground horizontal plate for three
unequal strength jets (Uo1=Uo2=2Uo3) at H=45 cm…………………… 72
4.36 Flow visualization of three un equal impinging jets (Uo1=Uo3=0.5 Uo2)
at H=45 cm…………………………………………………………………… 73
4.37 Flow visualization of three un equal impinging jets (Uo1=Uo2=2 Uo3)
at H=45 cm………………………………………………………………… 73
4.38 Axial mean velocity profiles for three equal and unequal impinging
jets at H=45 cm……………………………………………………………… 74
4.39 Axial turbulence intensity profiles for three equal and unequal
impinging jets at H=45 cm ………………………………………………….. 75
4.40 Flow visualization of three impinging jets at H=70 cm……………………. 76
4.41 Axial mean velocity profiles for three equal and unequal
impinging jets at H=70 cm…………………………………………………. 77
4.42 Axial turbulence profiles for three equal impinging jets at
x/tp =46, 48, 56, 68, 80 and H=70cm 77

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LIST OF SYMBOLS
H : distance between vertical impinging plate and jets exit
plane [ cm]
J : velocity momentum [m2
/s2
].
Jp : pressure momentum [m2
/s2
].
Jt : total momentum [m2
/s2
].
Jo : jet exit momentum [m2
/s2
].
L : axial measuring distance from the jet exit [cm]
l : jet nozzle length (49 cm)
S : the distance between the centerline of the jets [ 17 cm].
tp : jet nozzle thickness [ 0.5 cm].
U, V, W : air velocity components in lab coordinate [m/s].
x , y , z : axial , lateral and vertical directions in the lab coordinates [cm]
Uo1 ,Uo2 ,Uo3 : jets exit velocity [ 45 m/s].
Ueff : effective velocity [m/s].
u', v', w' : velocity fluctuations components along x , y and z
respectively [m/s].
u'v', u'w', v'w : shear stress components [m2
/s2
].
Greek letters:
 : air density [kg/m3
].
321 ,,  : air velocity components in wire coordinates [m/s].

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CHAPTER - I
INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction
The impingement of jets in fluid mechanics has many extensive engineering
applications. Results of researches in this field are being utilized in several functions
and purposes, this includes cooling and drying operations, cleaning electronic
components, annealing of metal and glass, tempering operations, cooling turbine blades
and combustion walls, materials processing and manufacturing, and also in the design
of efficient (V/STOL) aircraft jets.
The investigation of the flow fields of impinging jets has been the subject of
considerable researches over the past 25 years, and still the focus of many significant
authors in the literature today. Researches topics under studies have been arranged and
classified on the basis of jets shape and configuration, this including confined or free
jet, single or multiple jets, turbulent or laminar flow jet, simple or complex jets, etc. It
is also classified on the basis of impingement surface where moving or stationary
surface is considered, with or without cross flow.
One of the important reasons behind investigating such flow fields is to furnish a
better understanding of complex flow fields produced by the impinging of multi-jets on
normal or inclined surfaces. The nearest application example of such area of research
can be seen from the jets produced by aircraft, rockets and missiles engines, in these
cases the optimization between near field engine flow configuration and far field
configuration is significant, it can only be achieved by a good engineering knowledge
1

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and understanding of the resultant flow field produced by the impinging of the
interacted engine jets with the ground. On this study, the project is mainly concerned
with the investigation of the flow field formed by the impingement of three two
dimensional parallel air jets on a vertical plate using hot-wire anemometer technique
and flow visualizations.
1.2 literature review
So far, many investigators have performed experimental and numerical studies to
predict the flow field structure and heat transfer of a single impinging jet with different
configurations, many have also presented empirical corrections based on their data,
however the new studies of the flow field of multiple jets are still few comparing to
single jet configuration, this is in spite of currently developed researches which are
being carried out on this field.
Now referring to literature and considering the most relevant papers to this project
concerning the impingement of jets on surfaces, we could find that, Elbanna et al [1],
studied the flow field structure generated by the impingement of two free parallel air
jets normally on a flat plate, the experimental results with flow visualization have
shown good measurements of mean velocities, pressure, and turbulent intensities and
revealed the influence of both geometric parameters and the relative strength of both
jets on the fountain and other flow properties.
Barata [2], also studied the characteristics of three-dimensional fountain flows
produced by the impingement of three-axisymmetric jets on a ground plane with cross
flow. The experimental results showed the presence of a complex vortex formed around
each impinging jet and fountain upwash flow , the results were then confirmed
numerically using k-ε model , Barata et al [3],[4] also found experimentally the mean

25
and turbulent velocity characteristics of single and multiple jets impingement through a
low velocity cross flow , they studied the shear layer surrounding the jets , the
impingement regions , and fountain upwash flow zone and measured the turbulent
structure parameters , their comparison of predicted and measured results shows that
the k-ε model is useful for the prediction of the mean flow field but fails to predict the
turbulent structure due to near- wall viscous effects.
On the other hand a research on an axisymmetric jet impinging on concave surfaces
has been studied by Hibara and Sudou [5] ,their resulting figures showed the
distribution of mean velocity ,turbulence energy , Reynolds stress components and the
static pressure.
Flow visualization technique is an interesting tool that provides valuable insight into
complex flow fields. This important tool is used regularly in air flow experiments. It
shows the behavior of the jet flow stream lines and verifies the shape of flow direction.
It is also essential for estimating a velocity profile and confirming the graphical
measurements data, moreover flow visualization is significant tool to insure the jets
symmetry shape, shows any jets deflection and describe any vortices that may occur in
the flow field. Several flow visualization techniques are used by different investigators
in the literature. Some methods are based on using a simple technique of spreading a
mixture of Kerosene and chalk on plane sheet .Elbanna and Sabbagh [6 ] conducted
experiments on flow visualization for two free jets impinging on vertical plate .The
results showed good velocity profiles , visualization and stress distributions. Other
investigators used smoke generators or Lazer Induced Fluorescence (LIF) techniques
[8]. Also Bernard [7] has employed different visualization techniques in order to
describe the flow pattern due to 15 jets impinging on a plane wall. The spreading over
method revealed the jet influence on the impinged surface and Lazer visualizations

26
sheet emphasized complex vortical structures. Velocity measurements were realized to
confirm this observation and to specify flow pattern. In addition, Bernard [9] has also
studied the wall flow generated by these jets. A comparison between two cases of flow
visualization techniques of two impinging axisymmetric circular jets have been carried
experimentally by Shoe-B et al [8], in one case they used Lazer induced fluorescence
(LIF) to visualize the flow structure, while they utilized smoke in the second.
Quantitative information has been obtained from these visualized flow regimes using
two different digital imaging systems. Results were presented for both the jet profile
shapes and the rate at which the jet expands in the downstream direction. These results
compare favorably with data obtained using established anemometry techniques.
On the other hand Behrouzi [10], presented predictions of the flow of a twin-jet
impingement on ground plane using the standard two-equation k-ε turbulence model,
the predictions were compared with Lazer Doppler Velocimetry experimental results.
The fountain formation region was qualitatively predicted .The quantitative under-
prediction of fountain development characteristics was observed to be around 50%, this
is probably due to fountain unsteadiness, which is not included in the steady state
Computational Fluid Dynamics predictions. Lazer Doppler Velocimetry measurements
were also used by Behrouzi and McGuirk [11] in order to study a closely spaced pair
of jets with same or different jet velocities. The jets interact with each other, with a
cross-flow and with an opposite solid wall .Emphasis was placed on the presentation of
the mean velocity and r.m.s contours in the fountain formation region between the jets.
The effect of jet imbalance and velocity ratio was studied, and then preliminary
Computational Fluid Dynamics predictions of the flow using a k-ε turbulence model
were presented.

27
Many researchers have carried out several numerical and computational studies on jet
impingement in the literature [12-17], most computational results in these researches
were compared and confirmed experimentally using either Lazer Doppler Velocimetry
or hot wires techniques .In addition , Dianat [18] has modified a k-ε turbulence model
to use it as the basis of predictions of the flow results from the orthogonal impingement
of circular 2-dimensional jets on a flat surface. Results in general confirmed the
superiority of the Reynolds stress transport equation model for predicting mean and
fluctuating velocities within the region of such flow.
The vertical take-off and landing military airplane (VTOL) working on the rough
ground was studied by each of Chuang and Cheng in [19]. They have employed the
SIMPLE-C algorithm, power-law scheme, two equation k-ε turbulent models, and
alternating direction implicit method in numerical simulation. The properties of the
flow field structure of the impinging twin-jet such as pressure, velocity, turbulent
kinetic energy and lift force under the effects of different width and height were solved
and shown. They have concluded that the lift force is strongly affected by the squeezed
and shortened effects of recirculation zones induced beside the twin-jet inlet. Similarly
Behrouzi and McGuirk [20],also have reported an experimental study of a closely-
spaced pair of interacting jets in the presence of both cross-flow and an opposing solid
wall , This experiment was used to gather validation data suitable for testing
Computational Fluid Dynamics model predictions of multi-jet ground impingement
flows.
Moreover, experimental and numerical studies of round high speed impinging jets with
varying nozzle height and pressure ratio were studied and presented by Knowles and
Myszko [21]. Wall jet growth was seen to be approximately linear with radius but
depend on nozzle height and pressure ratio.

28
On the other hand, Disimile and Savory [22] have investigated a mixing region of
two identical incompressible air jets at two different angles (45º,35º) . Their work has
confirmed that the growth of the 45-deg jet after impingement in the plane normal to
the nozzle plane was greater than that in the 35-deg case, but in the nozzle plane the
growth rate for both cases was identical and similar to that of a single jet. Similar to
this approach , a mixing mechanisms in a pair of liquid jets have been carried out by
Ashgriz, Brocklehurst and Talley [23].
Furthermore, an experimental research has been carried out by Knowles and Bray
[24] to study the flow fields associated with single and twin jets impinging in cross-
flows, using ground plane pressure profiles and flow visualization. Parameters such as
cross-flow-to-jet, velocity ratio, cross-flow boundary-layer thickness, nozzle height and
their effect on the position of the ground vortex have been investigated. Results showed
that the ground vortex moves away from the nozzle centerline as cross-flow-to-jet
velocity ratio is decreased, also the rate of change of position, however, depends on
other parameters. In addition to this work they have used the PHOENICS code [15] to
model the flow field surrounding subsonic and under-expanded jets impinging on a
ground plane in the presence of a cross-flow, for cases with both a fixed ground plane
and a 'rolling road'. The ground vortex formed in cross-flow is shown to move with
varying effective velocity ratio and with rolling road operation in the same manner as
experimentally observed.
Prasad, Mehta, and Sreekanth [25], also conducted an experimental and numerical
studies to investigate the impingement flow field produced on a typical axisymmetric
jet deflector. They concluded that these experiments will be useful for the design of a
typical axisymmetric jet deflector during the liftoff phase of a rocket.

29
An under-expanded sonic jet impinges on a perpendicular flat plate, a shock wave
forms just in front of the plate and some interesting phenomena can occur in the flow
field between the shock and the plate. This phenomenon was indicated by Iwamoto
[26] who presented experimental and numerical results on the flow pattern of this
under-expanded impinging jet. In the numerical calculations the two-step Lax-
Wendroff scheme was applied, assuming inviscid, axially symmetric flow. Some of the
pressure distributions on the plate showed that the maximum pressure did not occur at
the center of the plate and that a region of reversed flow exists near the center of the
plate. Nakabe and et al [27] have presented a study to examine the interaction between
two inclined impinging jets in in-line and staggered arrangements with cross-flow. It
was observed that the geometrical arrangement of the inclined jets had an influence on
the interaction between the two jet flows, on the vortical structures generated in the
downstream of the jets, and eventually on the enhanced regions of jet impingement heat
transfer. They had cooperated before this experiment also in a similar project approach
by studying the generation of longitudinal vortices in internal flows with an inclined
impinging jet for enhancing the target plate heat transfer [28]
Jet array configurations also have been subjected recently to some studies by
researchers, Arjocu and Liburdy [29] have studied the large scale structure formation
of a three-by-three jet array at low Reynolds number (466 and 1474) , this is as in the
case of cooling electronic components. The effects of the impingement distance were
studied over a range of impingement distance for jet diameters of two to seven. They
concluded that distinct changes were noted in the resulting vortex structure when the
impinging distance increases from 2 to 6 jet diameters. They also conducted an
experiment to investigate the near surface turbulence characteristics of an impinging
elliptic jet array at low Reynolds number [30]. In this experiment the dynamics of a

30
three-by-three elliptic jet array were analyzed relative to the flow structures within the
array. Two jet aspect ratios were used .The effects of impinging distance were studied
in the range of one to six jet hydraulic diameters. Also flow visualizations were used
for the identification of structures and quantitative analysis. The results have shown
that the integrated surface layer vorticity depends on the jet aspect ratio and
impingement distance.
1.3 Research objectives
In this thesis we extend the study on jet impinging by investigating the flow field of
three free parallel two-dimensional jets impinging on a flat plate normal to their axes.
The main objectives of this study could be summarized in the following points :
1. To predict the flow field of three interacting free parallel two-dimensional jets
impinging on a plate normal to their axis using hot wire technique. The study
includes the influence of changing some parameters on the resultant flow field
such as the location of the vertical plate and / or jets velocities.
2. To investigate the turbulence structure in the interacting jets upstream, wall jets
and fountains.
3. To study the resulting flow field by flow visualization technique.
4. To study the jets pressure distribution along the vertical impinging plate and the
lower wall of the test rig.
In addition the results of this investigations will help in understanding the flow
structure of two types of different wall jets interactions, specially between the middle
jet and the two outer jets after impingement .The application of the results is important
in vertical take off and landing aircrafts jets and in the application of multi jets for
cooling purposes such as cooling turbine blades.

31
CHAPTER – II
EXPERIMENTAL SETUP
This chapter demonstrates the experimental setup and instrumentations used for the
measurements of this work. Some detail description about the experiment test rig is
presented in section 2.1. The measuring instruments and tools are covered in section
2.2. Finally section 2.3 discusses the wire calibration in some details.
2.1 Setup and alignment
An existing test rig for jet studies [6] has been modified to suit the present research
requirements. The test rig consists of two supported parallel walls confining three
identical jets blocks as shown in Fig. 2.1 below.
Figure 2.1 Test rig schematic diagram
air
flo
w
air flow
scr
ee
ns
Dimensions in mm
9

32
(b) Modified nozzle top
view
The width of each wall is 2 m in the lateral direction and the length is 3 m in the axial
direction. The jet blocks are separated by equal distances and connected to three air
blowers to supply air. Before air converges to the nozzle exit, it passes through three
settling chambers for producing uniform velocities along the length of the slots .Each
jet block contains three grids to reduce the size of turbulence. The contraction ratio of
the nozzles in the horizontal direction is 13:1, each nozzle slot has a width tp=5 mm and
a length l=490 mm in the vertical direction. The exit frame of each jet nozzle outlet in
this experiment was modified to a new design as shown in Fig.2.2, in order to correct
an observed jet deflection in the old nozzle. Each nozzle slot, spans all of the distance
between the two confining walls to prevent air leak into the low-pressure regions
between the jets.
Figure 2.2 Tope views of the old and the modified jet nozzles.
The vertical impinging plate is set on moving part between the two horizontal confining
walls normal to the nozzles axes as shown in Fig.2.3. The confining walls extend 1 m
to either side of the midline between the three jets; traverse is carried out spanwise of the
(a) Old nozzle top
view

33
nozzle slot and in the lateral direction to determine the degree of uniformity of the flow
emanating from the nozzle.
Figure 2.3 Side view of jets blocks and vertical impinging plate .
The nozzles are designed with a contraction ratio of 13 :1 as mentioned before and
aspect ratio of 89:1, this to insure the two-dimensionality of the flow field. Overall
experiment test rig photos are shown in Figs. 2.4-2.8.
Figure 2.4 Traverse mechanism side view

34
Figure 2.5 Air blowers feeding the three jets .
Figure 2.6 Side view of jets blocks

35
Figure 2.7 Dynamic flow board for data acquisition system
The mean velocities of the flow and the turbulent intensities are measured using DISA
5600 hot-wire anemometers connected to a data acquisition system (as will be shown
later). The hot-wire anemometer is fixed on a locally modified traverse mechanism .
This mechanism is used for axial and lateral flow measurements, as shown in Fig. 2.8.
In this experimental research work , flow visualizations of the impinging jets are
carried out in order to show the behavior of the jet flow stream lines and verify the
shape of flow direction. This is done by spreading a mixture of kerosene and chalk
powder on a black Perspex sheet placed horizontally on the test rig lower wall between
the jets exit plane and the vertical impinging plate.

36
Figure 2.8 Traverse mechanism components
Finally the average flow field pressures and surface pressure along the lower plate
and the plate normal to the flow is measured using pressure taps of 0.5 cm diameter
evenly distributed in the middle part of the lower wall and vertical plates and
connected to a pressure transducer or electronic manometer as shown in Fig. 2.9.

37
Figure 2.9 Pressure electronic manometers.
2.2 Instrumentations
Constant Temperature Anemometry (CTA) or Hot Wire Anemometry - is a widely
accepted tool for fluid dynamic investigations in gases and liquids and has been used as
such for more than 50 years. It is a well-established technique that provides information
about flow velocity. There are several types of hot wires probes currently being used ,
the very famous types used in the measurements are single normal wire ,single slanted
wire , X-wire and triple wire . All velocities and velocity fluctuations across the jets
flow field in the experiment were measured using two types of constant temperature hot
wires probes manufactured by Dantec Company, namely, the single normal wire and
the triple wire. The following sections describe briefly these probes.
2.2.1 Single normal wire probe
The wire configuration used in the experiment is known as normal or straight wire
probe, it is called Miniature Wire Probe Platinum-plated tungsten (55P01). The wire as

38
shown in Fig. 2.10 has 5 m diameter and 1.2 mm length, it has straight prongs and
sensor perpendicular to probe axis. The wire is welded directly to the prongs and the
entire wire length acts as a sensor. The probe body is a 1.9 mm diameter ceramic tube,
equipped with gold-plated connector pins that connect to the probe supports by means
of plug-and-socket arrangements. It is a general purpose probe recommended for most
measurements in one-dimensional flows of low turbulence intensity. The accuracy of
turbulence measurements may be reduced because of interference from the prongs. On
the other hand, the more rigid construction makes it more suitable for high speed
applications without the risk of self-oscillation. It can be used when measuring mean
and fluctuating velocities in free-stream one-dimensional flows and it mounts with the
probe axis parallel to the direction of the flow. The single-sensor wire probes are
available in five different configurations.
Figure 2.10 Single wire probe (Miniature wire type by Dantec Dynamic
site www.dantecdynamics.com).
2.2.2 Triple-sensor gold-plated wire probe
The Triple-sensor gold-plated wires probe as shown in Fig. 2.11 is available in one
straight configuration for gas applications only, it is referred to as, Gold-plated tri-axial

39
probe (55P91). It has three mutually perpendicular sensors, consisting of gold-plated
wires. The gold-plated probes have 5 µm diameters, 3 mm long platinum-plated
tungsten wire sensors. The wire ends are copper and gold-plated to a thickness of 15 to
20 µm, leaving an active sensor, 1.25 mm, on the middle of the wire. They are designed
for measurements in high-turbulence flows of three-dimensions. The sensors form an
orthogonal system with an acceptance cone of 70.4°. The prong ends are all
perpendicular to the sensors. This gives minimum prong interference and increases the
accuracy, when the three probe signals are decomposed into velocity components. It is
used for measurement of the U, V and W velocity components in an instationary three-
dimensional flow field and provides information for calculation of the full Reynolds
shear stress tensor. It also mounts with the probe axis in the main flow direction. The
resulting velocity vector must be within the acceptance cone.
Figure 2.11 Triple wire probe provided by Dantec Dynamic site
www.dantecdynamics.com
Sensor identification
3 sensors perpendicular to each
other inside a sphere of 3 mm

40
2.2.3 Data Acquisition
The data acquisition system used to collect and analyze the turbulent flow data is called
" AcqWire " devolped by Dantec company . "AcqWire " is an application software for
Constant Temperature Anemometer (CTA) system intended for experimental
measurements and analysis of fluid flow. The program performs data acquisition, data
processing and file manipulation. It can be used with any thermal sensor anemometer
systems which output an analogue signal in the range 0-10 v. This signal is a
continuous analogue voltage .In order to process the signal digitally it has to be
sampled as a time series consisting of discrete values digitized by an analogue-to-
digital converter (A/D board), see Fig.2.7.The parameters defining the data acquisition
are the sampling rate (SR) and the number of samples, (N). They together determine the
sampling time as T=N/SR. The values for SR and N depend primarily on the specific
experiment. The main characteristics of the data acquisition system are summarized in
the following points :
 Resolution: min. 12 bit (~1-2 mV depending on range).
 Sampling rate: min. 100 kHz (allows 3D probes to be sampled with approx. 30
kHz per sensor).
 Simultaneous sampling: (if not sampled simultaneously there will be phase lag
between sensors of 2- and 3D probes)
 External triggering: (allows sampling to be started by external event)
 Signal Conditioning of anemometer output , see Fig. 2.12.
 Increases the AC part of the anemometer output and improves resolution.
 Allows filtering of anemometer
- Low pass filtering is recommended

41
- High pass filtering may cause phase distortion of the signal
 Sample rate and number of samples: Time domain statistics (spectra) require
sampling rate 2 times the highest frequency in the flow.Amplitude domain statistics
(moments) require uncorrelated samples. Sampling interval min. 2 times integral time
scale.Number of samples is sufficient to provide stable statistics (often several
thousand samples are required).Proper choice requires some knowledge about the flow
aforehand, [32].
Figure 2.12 Constant Temperature Anemometer layout diagram (by Dantec
Dynamic site www.dantecdynamics.com)
2.3 Calibration of hot-wires
Calibration establishes a relation between the CTA output and the flow velocity. It is
performed by exposing the probe to a set of known velocities, U, and then record the
voltages, E. A curve fit through the points (E,U) represents the transfer function to be
used when converting data records from voltages into velocities. A continous
relationship is provided by calibraion polynomial which is computed by curve fitting
the calibration points.The output of the calibration polynomial is the effective cooling
velocity which the probe senses. It should be equal to the reference velocity component
when the sensor is normal to the fluid velocity at the time of calibration , ie Ueff =U.

42
W
U
V
yi
xi
zi
U
The anemometer output for the "jth
" sensor, Ej is related to the corresponding effective
velocity, Ueffi , by the calibration polynomial.
2
1 2
n
eff O j j n jU C C E C E ......C E    (2.1)
where CO , C1 .....Cn, are called the calibration coefficients. The effective cooling
velocity, Ueff , is equivalent to the linearized anemometer output.
The laboratory coordinate system usually defined relative to the experimental facility
by the orthogonal unit vectors ( x y zi ,i ,i ). The fluid velocity vector U can be written
according to the laboratory coordinates as:
x y zU U i V i W i   (2.2)
where, U, V, W, are the components of U in the directions of x, y, z,
respectively as shown in Fig .2.13 below .
Figure 2.13 Velocity components vectors in the laboratory coordinates.

43
3i
1i
2i
1
2
3
U
The wire coordinate system is a right-hand ruled Cartesian coordinate system defined
relative to the axis of the sensors. A sensor aligned with wire coordinate axis 1 is
called sensor 1, a sensor aligned with axis 2 is sensor 2 and a sensor aligned with axis 3
is sensor 3. The wire coordinate is also defined by the orthogonal unit vectors 1 2 3i ,i ,i .
A fluid velocity vector, U decomposed into wire coordinates is described by:
1 1 2 2 3 3U i i i     (2.3)
where 1 2 3, , ,   are components of U in the direction of 1 2 3i , i , i , respectively as
shown Fig.2.14below.
Figure 2.14 Velocity components vectors in the wire coordinates.
The thermal sensor is cooled by velocity components in all directions. In this respect
the theory of angular response of thermal sensors began with the concept of "Cosine
Law". This law is a model for the angular response of thermal sensors which assumes

44
the sensor to be insensitive to the component of velocity parallel to the sensor.
Therefore the Cosine Law can be defined using wire coordinates directions as:
2
3
2
2
2
1 0 effU
2
3
2
1
2
2 0 effU (2.4)
02
2
2
1
2
3  effU
The position of the zero term in the above three equations reveals the major assumption
involved in the Cosine Law: there is no contribution to the effective cooling of the
sensor in the direction of the wire.
However an improved model was developed by Finn Jorgensen of Dantec Electronic,
Denmark [31], to account for the distinct contributions to the effective cooling velocity
of the three velocity components in the wire coordinates system.
So, by interfering the effect of Jorgensen's principle on the Cosine Law of the previous
3 wire equations they were modified to:
2 2 2 2 2 2
1 1 2 3    eff y pU k k
2 2 2 2 2 2
2 1 2 3    eff p yU k k (2.5)
2 2 2 2 2 2
3 1 2 3eff p yU k k    
The yaw factor, ky provides a contribution to the effective cooling velocity due to the
velocity component tangential to the wire. The pitch factor, kp , provides a contribution
to the effective cooling velocity due to the velocity component normal to the wire and
perpendicular to the plane of the supports. Typically, ky =0.15- 0.2, and kp=0.9-1.02.

45
Jorgensen's equations are especially used for triple sensor probes, since at any given
point in the fluid the three unknown velocity components can be solved for using the
set of three equations.
The application of Cosine Law and Jorgensen's equations on the two probes types used
is given in the following, sections.
Single Sensor Probe:
Figure 2.15 Single Sensor Probe:
With a single sensor probe as shown in Fig. 2.15 above , it is usually straightforward to
align the wire coordinate system with the laboratory coordinate system. For this
orientation, zyx ii,ii,ii  321 , and W,V,U  321 .
Now from the Cosine Law and for one dimensional flow where V=0 and W=0, we
obtain:
2 2
effU U or U=Ueff2 (2.6)
Probe stem
Z
x

46
The result shows that the linearized anemometer output, Ueff of a single sensor probe is
a direct indication of the instantaneous component of fluid velocity in the x direction of
the laboratory coordinate system. It has to be noted that the effective velocity
measurements are collected after all wires have been calibrated.
Triple Sensor Probe:
Figure 2.16 Triple sensor probe.
The triple sensor probe as shown in Fig. 2.16 above has three sensors mounted
orthogonally. The three sensors define the 3 directions of the wire coordinate system.
Using Jorgensen's equations with the planes of supports defined previously we can
write:
2 22 2
1 1
2 2 2 2
2 2
22 2 2
33
1
1
1
    
    
     
             
y peff
eff p y
eff p y
k kU
U k k
U k k
(2.9)
Probe stem
45°
55°
35°
3
1
z
x
35°
2
y

47
Solving for the components of U in wire coordinates, yields:
12 2 22
11
2 2 2 2
2 2
2 22 2
3 3
1
1
1

    
    
      
            
y p eff
p y eff
effp y
k k U
k k U
Uk k
(2.10)
To transpose the velocity vector from wire to laboratory coordinates, the components of
the vector in wire coordinate should be multiplied by the direction cosines of the solid
angle subtending the unit vectors of the two coordinate systems. This can be expressed
mathematically as:
1
2
3
ij
U
V cos y
W
  
  
   
      
(2.11)
where yij is the solid angle subtended by the unit vectors i j( i ,i ) , i=1,2,3 ,j=x,y,z.
Assume the probe stem is horizontal and defines the x direction, the vertical direction
defines the z direction, wire 3 is in the vertical plane as shown in the previous figure .
The direction cosine matrix for Dantec triple sensor probes [31] is given by:
45 35 3 45 35 3 54 7
45 45 0
45 35 3 45 35 3 35 3
o o o o o
o o
ij
o o o o o
cos cos . cos cos . cos .
cos y cos cos
cos sin . cos sin . cos .
 
 
  
   
(2.12)
This is the default transformation used to obtain the velocity components U, V, W in
laboratory coordinates defined above.

48
Now if the instantaneous velocity components of the jets flow are determined then the
velocity fluctuations components also can be determined as:
__
'
__
'
__
'
u U ( t ) U
v V ( t ) V
w W ( t ) W
 
 
 
(2.13)
where the mean velocity components are determined from :
1
1
N__
i
i
U U
N 
  ,
1
1
N__
i
i
V V
N 
  ,
1
1
N__
i
i
W W
N 
  (2.14)
Now the mean square value of the velocity fluctuations components are defined as
2 2
1
1
N
'
i
i
u (U U )
N 
  ,
2 2
1
1
N
'
i
i
v (V V )
N 
  ,
2 2
1
1
N
'
i
i
w (W W )
N 
  (2.15)
Consequently the root mean square value of the velocity fluctuation components can be
determined as:
2
 '
rmsu u ,
2'
rmsv v ,
2'
rmsw w
(2.16)
The level of turbulence or the turbulence intensity components then can be calculated
as :
rms
ti
u
u
U
 ,
rms
ti
v
v
V
 ,
rms
ti
w
w
W

(2.17)

49
On the other hand the Reynolds shear stress components can be calculated by the
relations:
1
1
N
' '
i i
i
u v (U U )(V V )
N 
  
1
1
N
' '
i i
i
u w (U U )(W W )
N 
   (2.18)
1
1
N
' '
i i
i
v w (V V )(W W )
N 
  
All above equations are computationally determined using Quick Basic program for
faster calculations of results (see Appendix-III).
Calibration of Hot wire experimentally:
For better and accurate results both triple and normal single wires probes are calibrated
before each measurement set. A single probe calibration was carried out in the
laboratory using a round jet as shown in Fig.2.17. The wire is set very near to the jet
exit opening with the probe aligned parallel to the flow direction .The air blower is
then started at the highest jet exit velocity (Uo=45 m/s), while the probe is adjusted
back and forth near the jet exit ,the minimum possible turbulence intensity level should
be achieved by adjustment . The jet exit velocity could be found from the dynamic
pressure at the jet exit using electronic manometer. At the highest jet velocity the
corresponding wire voltage is measured also using Dantec Acqwire software . The
blower speed is then reduced gradually until the lowest blower velocity value is
reached. At each blower speed the jet velocity and the corresponding wire voltage are

50
measured. The velocity values should cover all the jets velocity range in the flow field
span .The resultant calibration (velocity-voltage) curve is then fitted with minimum
possible standard deviation points using the Acqwire software.
The calibration of the triple wire is also required before use and could be achieved by
the same procedure of the single wire calibration process, however there are additional
steps that should be accounted for this calibration. The triple wire probe is set near the
jet exit plane first and then tilted by 35o
from the axis of the jet centerline , after that
each wire is set normal to the jet centerline and calibrated individually while following
a similar procedure to that applied to the single wire as stated above. Different velocity
values and corresponding wire voltages are applied and measured at each wire. Fig.
2.18 shows a sample set of calibration curves of the single and triple wire probes.
(a) round jet side view
(b) round jet front view
Figure 2.17 Side view and front view photos of the round jet.

51
(a) Single wire
1.6
1.8
2
2.2
2.4
2.6
2.8
5 10 15 20 25 30 35 40 45 50
Effective velocity (m/s)
E,volt
1.6
1.8
2
2.2
2.4
2.6
2.8
5 10 15 20 25 30 35 40 45 50
Effective velocity (m/s)
E,volt
wire 1
wire 2
wire 3
(b) Triple wire
Figure 2.18 Calibration curves for (a) single and (b) triple wire probes

52
CHAPTER – III
MEASUREMENTS AND FLOW VISUALIZATION
This chapter explains the method and the steps of taking measurements and readings
in this project. Jets symmetry check is important in the measurements and this is
discussed in section 3.1. The measurement techniques results using single and triple
wire probes are then presented in section 3.2. Sections 3.3-3.5 introduce the method of
taking measurements of two and three planar free and impinging jets. Finally the flow
visualization technique of the impinging jets is discussed in section 3.6 .
3.1 Symmetry Check
Before taking any measurements the jet symmetry is checked. To confirm jet
symmetry, the measurements of mean velocity at different locations across the jet flow
field should be identical. This was done in the lab for the three jets using single normal
hot-wire probe. The test of symmetry for jets was conducted by taking measurements at
three axial locations across the flow field of each jet. Data were collected at 20 points
in the lateral direction for each jet. On this basis jets symmetry was checked and the
results were symmetric for all locations. Figs.3.1-3.3 show the velocity profiles for
symmetry check for the three jets. Obviously seen in these figures that the three
velocity profiles of jet 1and jet 3 are approximately overlap but for jet 2 there is little
deviation. This deviation is appeared while many trials were applied to the jet nozzle
outlet in order to correct this deviation during design process.
30

53
0.6
0.7
0.8
0.9
1
1.1
-0.14 -0.1 -0.06 -0.02 0.02 0.06 0.1 0.14
y/L
for x/tp=60
for x/tp=100
for x/tp=140
m
U
U
0.6
0.7
0.8
0.9
1
1.1
-0.14 -0.1 -0.06 -0.02 0.02 0.06 0.1 0.14
y/L
for x/tp=60
for x/tp=100
for x/tp=140
m
U
U
0.6
0.7
0.8
0.9
1
1.1
-0.14 -0.1 -0.06 -0.02 0.02 0.06 0.1 0.14
y/L
for x/tp=60
for x/tp=100
for x/tp=140
m
U
U
Figure 3.1 Velocity profiles to check Figure 3.2 Velocity profiles to check
jet (1) symmetry . jet (2) symmetry .
Figure 3.3 Velocity profiles to check
jet (3) symmetry .

54
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
y/L
Current Result
Elbanna and Sabbagh result [6]
m
U
U
The jets symmetry results were compared also with similar previous studies conducted by
Elbanna and Sabbagh [6] , as shown in Fig. 3.4 .The observed deviation in the figure
between the two resultant velocity profiles also came from the difference in the jet nozzle
outlet design in the two studies as shown early in Fig.2.2 .
Figure 3.4 Comparison of jets symmetry check between
current and perivous studies.
3.2 Comparison of Single and Triple wire measurements
In this project, single wire probe was used to measure the air flow velocity and
fluctuation in one direction, triple wire probe was used to measure mean velocity and
velocity fluctuations in three directions along the flow field. The concept of constant
temperature anemometer reading is that, the velocity is measured by its cooling effect on a
heated single sensor. A feed-back loop in the electronics keeps the sensor temperature
constant under all flow conditions. The voltage drop across the sensor thus becomes a
direct measure of the power dissipated by the sensor. The anemometer output based on
the calibration file therefore represents the instantaneous velocity in the flow. All

55
0.6
0.7
0.8
0.9
1
1.1
-0.14 -0.1 -0.06 -0.02 0.02 0.06 0.1 0.14
y/L
Single wire
Triple wire
m
U
U
experimental measurements were taken manually across the jet at specified locations.
To compare the velocity readings using single and triple wires probes, the velocity
measurements were conducted for a single jet at 45 cm distance from jets exit plane
using both wire techniques. Results are graphically shown in Fig. 3.5. It was concluded
that the two results are identical and approximately overlap.
Actually, it was more suitable to use triple wire for flow measurements if all velocity
components in all direction were required. In this project single wire probe was easier
and more convenient to use in conducting impinging region measurements or where the
flow contains vortices of known direction.
Figure 3.5 Velocity profiles using single and triple wire
measurements for single free jet at L=50 cm.
3.3 Two parallel free jets measurements
Single wire was used for measurements of axial average velocity at different locations
for the two free jets arrangement, this was done to compare and check the velocity

56
distributions crosswise the two jets with similar studies in the literature [6] as shown in
Fig.3.6.
Figure 3.6 Comparison of Axial velocity profile at x/tp=20
between current and perivous studies.
Measurements were taken at four axial distances from jets exit plane, namely 10, 25, 30
and 35 cm. At each location 20 points on each side of the centerline of the two parallel
jets were measured. The measurements start after aligning wire probe properly with the
jets centerline. Wire probe is set exactly normal to the flow using right angle ruler .The
probe is transferred automatically any / where in the lateral or axial direction using the
traverse mechanism. The starting measuring point is the jets centerline .At this point the
probe is held to acqwire data using a sampling rate of 2048 , then the collected data is
saved as an ASCII file mode for later processing of data using code in QuickBasic.
The probe is moved then to next point and the same procedure is followed to save and
collect data. The same steps are repeated at all points along the traverse direction of the
flow field. The traverse mechanism should be moved carefully to the new distance, this
was carried out manually in the lab using screwed steel bar connected to the traverse
mechanism.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
y/s
Current result
Elbana & Sabbagh result [6]
1o
U
U

57
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
y/s
x/tp=20
x/tp=50
x/tp=60
x/tp=70
1o
U
U
0
0.1
0.2
0.3
0.4
0.5
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
y/s
u'/Uo1
x/t=20
x/t=50
x/t=60
x/t=70
2'
u
U
Figure 3.7 shows the graphical presentation of mean velocity ratio at those locations for
two parallel free jets, while Fig. 3.8 shows the axial turbulence intensity profiles for
two equal free jets.
Figure 3.7 Axial mean velocity profiles of downstream merging
region of two free parallel jets.
Figure 3.8 Axial turbulence intensity profiles for double jet arrangement .

58
0.12
0.16
0.2
0.24
0.28
0.32
0.36
0.4
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
y/s
x/t=30
x/t=50
x/t=80
x/t=140
1o
U
U
3.4 Three parallel free jets measurements
The experimental study of three parallel free and impinging jets measurements is the
main goal in this project. In free jets study triple wire technique is used in all
output measurements including average velocity components ratios
(U/Uo1,V/Uo1,W/Uo1), Reynolds normal stress components (u'2
/ Uo1
2
, v'2
/ Uo1
2
, w'2
/Uo1
2
)
and Reynolds sheer stress components (u'v'/Uo1
2
, u'w'/Uo1
2
, v'w'/Uo1
2
). The
replacement between single and triple wire probe was required some care in the
experiment, this was necessary to avoid wires breakage due to surface contact. Also
when the probes are replaced, each jet was adjusted and aligned properly with the new
wire probe stem to insure good and accurate measurements.
In this experiment four axial distances 15, 25, 40 and 70 cm were selected along the
flow direction of the interacted jets for the measurement of the velocity components as
shown in Fig.3.9.
Figure 3.9 Axial mean velocity profiles of three free parallel jets
During the calibration process the triple wire was oriented in such a way that wire 3 of
the probe must point up [32]. The wire probe should be aligned properly with the jet

59
nozzle centerline to avoid any asymmetry that may take place in the flow field later.
The movement of triple wire was controlled manually using remote control device
connected to the probe holding arm , this device is able to move the arm in lateral and
axial directions for measurements. Data was collected at each position using Acquire
data acquisition software at a sampling rate of 2048. The collected data is saved as
mentioned previously in ASCII files for later analysis by a computer program written in
QBasic language.
3.5 Three parallel impinging jets measurements
In these measurements, three parallel jets with equal velocities are impinged on a
vertical plate, this plate was placed normal to the jets air flow at different distances
from the jets exit 10, 20, 30, 45 and 70cm. At plate distance 70 cm from the jet exit
plane, the triple wire was used for the measurements of the impinging jets flow field, in
this confined flow two traverse distances were selected, one at 30 and the other at 60
cm from jets exit .The measuring points along these traverse locations were started
from the centerline of the middle jet which is also the center of the interacted jets
region see Fig.3.10.The measurements were taken at equally spaced points on the right
and the left side of the centerline.
S
Upwash Stagnation
points
Negative pressure
region
Impinging plate
Velocity profile
Figure 3.10 Schematic diagram of the flow field of three impinging jets

60
Data collection process is the same that described earlier in section 3.3. Measurements
were conducted after aligning the wire with the direction of the flow as mentioned
earlier. At 60 cm measuring distance wall jets exist after impinging, the wire probe was
rotated approximately 90o
from it's centerline , this is to make the probe normal to the
expected flow of the jets and consequently measure the flow velocity of the wall jet.
At the other selected plate distances (45,30,20 and 10 cm from the jets exit) , it was
detected that some rotating vortices and reverse flow may occurred at the locations of
measurements in the flow field as revealed by the visualization pattern In this case
triple wire was not used for the flow measurements in these regions .This was due to
the inflexible moving of the wire probe in these narrow regions and also to avoid any
wrong data which may caused by the random flow stream directions produced by
vortices . However a single wire was used for the measurements in these flow regions
.It was required a method to know the flow directions and to collect the correct flow
measurements. One trial was accomplished by setting the wire probe normal to the jets
exit air stream in the vortex region and then velocity components (U,V) are found by
rotating the wire two times toward the lab coordinates (x,y) based on the
corresponding reading values of Ueff1,Ueff2 . At each measuring point there are two data
that should be collected and saved , one is Ueff1 where the wire is parallel to the lateral
direction and the other is Ueff2 where the wire is parallel to the axial direction .Each of
these two velocities has two components (U,V) in wire or lab coordinates . Now
solving equation (2.5) for two dimensional case then U, V could be determined.
Consequently the corresponding velocity fluctuations and stresses could also be found.
This method was used in all other flow measurements at the above mentioned plate

61
distances. Table I.1 summarizes all distances of the impinging plate and the type of hot
wire used in the measurements.
On the other hand the surface pressure of the incident flow along the vertical
impinging plate and also the static pressure at all previous distances were measured,
these measurement were carried out using pressure taps of 0.5 cm diameter evenly
distributed on the middle part of the vertical plate , the taps are connected to a
pressure transducer and /or electronic manometer which gives the pressure reading .
3.6 Flow Visualization Technique
Due to the limited budget available to this research work , flow visualization is
obtained using the simple technique of spreading a mixture of kerosene and chalk on a
Perspex sheet placed horizontally between the jets exit plane and the vertical plate.
Four Perspex black sheets with different widths of 10, 20, 30 and 50 cm were used for
this purpose.
Good flow visualization was achieved after some experimental trials. The technique
is based on uniformly spreading a layer of light oil such as kerosene on black Perspex
sheet, fine chalk powder is then sprinkled uniformly on the oil layer across and along
the flow area using a piece of cloth. The sheet is set in front of the jets nozzle on the
lower wall of the test rig and parallel to the flow .Jets are then run and passed over the
chalk-oil mixture, the stream lines formed by the mixture reveal the shape of the
resultant flow field .The jets are stopped and the Perspex plate is left to dry for one or
two days and then photographed .This process was repeated many times in order to
obtain satisfactory flow visualization image of the resultant flow field.

62
Before conducting visualization experiments the jets are also adjusted so that they
have equal velocity strengths and flow symmetry, this was done each time the vertical
impinging plate is moved to a different position along the flow direction.

63
CHAPTER - IV
DISCUSSION OF RESULTS
In this chapter all results of free and impinging jets measurements are discussed.
Section 4.1 discuss the results of two and three free jets arrangements. The study of
three equal and unequal impinging jets results at different impinging plate locations is
presented in section 4.2. The results of the flow pressure distributions on the impinging
plate for equal and unequal impinging jets are discussed in section 4.3 and 4.4. The
static ground plane pressure results are also covered by these two sections.
4.1 Free jet measurements
This section shows the study of two and three free parallel jets results. In each
jetsarrangement, different measuring locations across the flow field were selected ,the
resultant shape of the interacted free jets is then studied . All calculations results of this
section are tabulated in Appendiix-1.
4.1.1 Interaction of two free parallel jets
Referring to the graphical presentation of two parallel equal free jets in Fig. 3.7, it can
be seen that at distance x/tp=20 , the mean velocity profiles of the two jets are identical
and the resultant bell shape of the two velocities looks very steep. The two jets did not
merge into each other yet at this distance. Figure 3.6 has shown a comparison of the
mean velocity profile obtained at x/tp=20 with that obtained by Elbanna and Sabbagh
41

64
[6] .The figure shows that the velocity profiles of the two studies have nearly similar
shape . However the shift in the two velocity readings is due to the difference in the
nozzles outlet design between the two cases, this gives a difference flow divergence at
the jet exit.
At x/tp=50 the velocity profiles of the jets indicate that the two jets start approaching
each other ,the flow velocities become weaker and the velocity profiles shape turn out
to be more flatter. Further increase in the distance from the jets exit plane (x/tp=60)
makes the two jets start to merge into each other and the velocity profiles become more
flatter. At x/tp= 70 the two jets almost have reached a complete merging, the resultant
velocity shape of the two jets become slightly similar to that produced by the single jet.
The turbulent intensity distribution at different measuring distances (x/tp=
20,50,60,70) of the two free jets is shown previously in Fig.3.8, at each distance the
figure shows high intensity near the edge of each jet with minimum intensity value at
the centerline of the jet., this is due to the nozzle edge effect and the air entrainment, it
disappears later as the two jets merge and become weaker.
4.1.2 Interaction of three free parallel jets
Figure 3.9 has shown graphically the interaction of three parallel free jets at different
locations .It can be seen from the figure that at distance of x/tp=30 the mean velocity
profiles of the three jets are approximately similar and the velocity bell shape of the
three jets looks steep and sharp. It clearly obvious at this distance that the merging of
the three jets did not occur yet and each jet is independent. At x/tp=50 the velocity
profiles of the jets indicate that the two side jets are starting to approach the middle jet.
The velocities strength get weaker and the velocity profiles shape become less

65
m
o
U
U 1
x/tp
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
Jet 1
Jet 2
Jet 3
sharpness. Further increase in the distance from the jets exit plane (x/tp=80) bring the
three jets to merge more into each other, the velocity shape become more flatter. At x/
tp=140 the three jets approximately reach a complete merging, the resultant velocity
shape of the three jets become similar to that produced by a single jet.
Figure 4.1 shows the variations of maximum velocity at the centerline of each jet with
axial distance. As shown from the figure that Um is decreasing with the increase in x/tp
until x/tp=80 then it becomes constant and equal for all jets.
Figure 4.1 Variations of maximum velocity along the centerline
of each jet with axial distance.
Figure 4.2 also shows the approach of the outside jets centerline to the middle jet. As
can be seen by the figure when the axial distance increases, the two outside jets are
attracted gradually to the middle jet until they merge.

66
-1.5
-1
-0.5
0
0.5
1
1.5
20 30 40 50 60 70 80 90 100 110 120 130 140
x/tp
y/s Jet 1
Jet 2
Jet 3
Figure 4.2 Trajectory of the central streamline of each of the three jets.
The variations of turbulent intensity components with lateral and axial distance for the
three jets are shown in Figs. 4.3 and 4.4 respectively.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
y/s
u'/Uo1
x/t=30
x/t=50
x/t=80
x/t=140
2'
u
U
Figure Figure 4.3 Axial turbulence intensity profiles in the merging region of
three free parallel jets

67
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
y/s
x/t=30
x/t=50
x/t=80
x/t=140
2
1o
v '
U
Figure 4.4 Lateral turbulence profiles in the merging region of three free
parallel jets.
It can be noted from these figures that the intensities profiles are shrinking and
reducing with the increasing in the distance from the jets exit plane. Turbulent
intensities in the axial direction look sharp near the jets nozzle comparing to that in the
lateral direction, this is due to the effect of nozzle edges and the entrainment of air.
Also the shear stress profile is presented in Fig. 4.5.
0
0.0003
0.0006
0.0009
0.0012
0.0015
0.0018
0.0021
0.0024
0.0027
0.003
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
y/s
u'w'/Uo1
x/t=30
x/t=50
x/t=80
x/t=140
2
1
''
OU
vu
Figure 4.5 Shear stress profiles in the merging region of three free
parallel jets.

68
As shown by the figure, the level of shear stress decreases with the axial distance from
the jets exit, it has very low overall values and could be neglected.
4.1.3 Variations of momentum in three parallel jets
The total conservation of momentum equation [32] state that
Time rate of change of the time rate of change of net rate of flow of linear
linear momentum of the = the linear momentum + momentum through
system of the contents of the control surface
the control volume
or
sys contents of c.v
sys cv cs
F F
D
U dV U dV U U dA
Dt t
  


 

 
  
The first term on the left is the total rate of momentum which is donated as Jt , the first
term on the right side could be neglected for steady flow and the second term in the
right is the rate of momentum leaving the control surface which is the jets velocity
momentum J and the jets pressure momentum Jp in this experiment . So the above
equation could be written as:
Jt= J + Jp
(4.1)
(4.2)

69
0
0.04
0.08
0.12
0.16
0.2
0.24
0.28
0.32
0.36
0.4
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
y/s
x/t=30
x/t=50
x/t=80
x/t=140
o
J
J
where Jt= 2 2'
cs
(U u ) dy  (4.3)
Jp = 2
c.s cs
p dy (U )  (4.4)
The integration in the pervious equation is an indication for total fluid particles
momentum in the entire system. It can be observed that the velocity fluctuation term is
introduced in the equation to consider the turbulence effect.
The distributions of velocity momentum J with axial distance for the three jets are
shown in Fig. 4.6, it can be seen that the velocity momentum profiles behave the same
trend as the velocity profiles shown previously in Fig. 3.9. The distributions of pressure
momentum Jp can be seen from the pressure distributions on the vertical plate which
will be shown later.
Figure 4.6 Variations of momentum in the merging region of three free
parallel jets

70
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100 120 140
x/tp
Jet 1
Jet 2
Jet 3
The variation of centerline momentum with axial distances for each jet is shown in
Fig.4.7. As shown by the figure , when the measuring distance from the jet exit
increases the kinetic energy decreases gradually, thus the maximum momentum also
decreases , this decrease is contributed to the entrainment of air with the jets stream. , at
x/tp=80, the maximum momentum does not change much with any further increase
beyond this distance.
Figure 4.7 Variations of flow momentum along the centerlin
each jet with axial distance.
4.1.4 Comparison between free jets arrangement results
The flow behavior of the dual jets and triple jets is similar. Figs.4.8-4.10 show the
velocity and turbulent intensity profiles of two and three jets .It can be seen from the
figures that in the two jets arrangement the jets start to approach each other earlier than
the three jets case, but as the axial distance from the jets exit increase the three jets
merge earlier than that of the two jet and the profiles look more steeper.

71
0.1
0.2
0.3
0.4
0.5
0.6
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
y/s
Three free jets
Two free jets
1o
U
U
0.16
0.2
0.24
0.28
0.32
0.36
0.4
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
y/s
Dual jets
1oU
U
0.12
0.16
0.2
0.24
0.28
0.32
0.36
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
y/s
Triple jets
1oU
U
Figure 4.8 Velocity profiles at x/tp=20 for two and three jets arrangements.
Figure 4.9 Velocity profiles at x/tp=50 for double and triple jets arrangements .

72
0
0.1
0.2
0.3
0.4
0.5
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
y/s
Three jets
2'
u
U
0
0.1
0.2
0.3
0.4
0.5
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
y/s
Dual jets
2'
u
U
Figure 4.10 Axial turbulence intensity profiles at x/tp=50 for double and
triple jets arrangements .
Figure 4.11 shows the growth profiles in the half jet width against the axial distance for
single and dual jets results which are obtained from ref.[6] .The figure includes also the
growth profile for triple jets result of the current study .It is clear that the half jet width
in single and dual jets increase more rapidly with distance than that for triple jet , this is
because the triple jets velocity profile become steeper with the increase in the distance
comparing to the single and dual jets case .

73
x/tp
0
2
4
6
8
10
12
0 20 40 60 80 100
Triple jets
Dual jets from ref.[6]
Single jet from ref.[6]
y0.5/tp
Figure 4.11 Growth of jet width with downstream distance for
single , double and triple jets arrangements.
4.2 Impinging jets results
This section discuss the comments on the results of the jets impinging on the vertical
plate as well as the results of single, double and triple impinging jets .All calculations
results of this section are tabulated in Appendix-I. The comments of results are
demonstrated on the basis of flow visualization and the graphical presentation of the
data collected of each jet arrangement, this is explained in the following paragraphs.
4.2.1 Single impinging jet
Referring to Fig. 4.12 below, it shows the visualization of single impinging jet at 45
m/ s exit flow velocity and impinging on a vertical plate placed at 45 cm from the jet

74
exit .It can be seen from the figure the formation of the upwash in the downstream flow
region .The figure shows also that the jet flow is broken down into two parts after
striking the impingement plate, one part forms the outside wall jet as moving flow
fountain and the other part is reflected back and interacted with downstream flow .The
jet is spreading more with the axial distance while the jet velocity strength gradually
decreasing .
Figure 4.12 Flow visualization of single impinging jet at H=45 cm
4.2.2 Three parallel impinging jets
Setting the vertical plate across the free jets path at different distances from the jet exit
plane cause changes in the resultant flow field shape. Figure 4.13 shows the changes of
the flow field shape for three impinging parallel jets of equal strength with changes in
the distances between the jets exit plane and the vertical plate.
Vertical
plate
Jet exit

75
Figure 4.13 Flow visualizations pattern for three equal impinging jets at
different plate distances.
The figure shows that each jet collides with the plate and produces two wall jets .These
two wall jets move away from the two outside jets (jet 1 & jet 3) after impinging. The
two other wall jets which are produced by the middle jet collide with the opposing two
(4.13e) H=70 cm
(4.13d) H=45
cm
(4.13c) H=30 cm
(4.13b) H=20 cm
(4.13a) H=10
cm

76
wall jets which formed by the impinging of the two outer jets on the plate and form
vortices. Figure 4.14 shows a similar earlier study on the visualization of two
impinging jets of equal strength at different plate locations [7]. It describes how the
nature of the flow field is influenced by changing the distance H between the nozzle exit
plane and the vertical plate.
Figure 4.14 Flow visualizations pattern for two equal impinging jets at different
plate distances [7].
(4.14a) H=15 cm
(4.14b) H=20 cm
(4.14d) H=50
cm
(4.14c) H=25 cm

77
0.12
0.18
0.24
0.3
0.36
0.42
0.48
0.54
0.6
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2
y/s
H=10
H=20
H=30
H=45
H=70
2
1
1
2
O
P
U
The figure shows also the existence of vortices, stagnations points and wall jets in some
flow field regions. The resulting flow field in this study seems less complex than the
three impinging jets case, this is because less jets interactions and impact flow take
place. In the following paragraphs the results of the flow field resulting from three
parallel jets impinge on a vertical plate are presented and discussed in more details.
1. Impinging plate distance H/tp =20 (H=10 cm):
At this distance the pressure profile as shown in Fig. 4.15 below shows high pressure
values on the vertical plate due to the high kinetic energy of the flow.
Figure 4.15 Pressure distribution across the impinging vertical plate at different
distances from the jets exit.
On the other hand Fig. 4.16 shows two vortices existing in the midway between the jets
exit plane and the vertical plate. These vortices are formed by the air entrainment
between the downstream moving jets and the upstream moving fountain.

78
Figure 4.16 Flow visualization of three impinging jets at H=10 cm
The figure shows also the outside wall jets which are produced by the two outer jets. In
this region the flow is very complex due to the small distance between the jet exit plane
and the vertical plate. The two opposing wall jets of the outer jets interact with the
middle impact jet and form a complex flow field, this result in a very weak middle jet,
see Fig.4.17a. In this figure it can be seen that the axial velocity profile has two high
values at the outer jets and low value at the middle jet , the lateral velocity profile
shows nearly equal maximum velocity value at the centerline of each jet but with lower
level comparing to the axial velocity . Fig.4.17b is corrected form of Fig.4.17a which
considers the flow direction and the negative values of the velocity components. This
figure was plotted with the aid of Fig 4.16 by following the flow direction using stream
lines in the visualization pattern at this plate distance.
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
y/s
MeanVelocityRatio
U/Uo1
V/Uo1
H=10
cm
Figure 4.17a Axial and lateral velocity profiles for three equal impinging
jets
at x/tp =10 and H=10 cm
Vertical plate

79
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
y/s
MeanVelocityRatio
U/Uo1
V/Uo1
Figure 4.17b axial and lateral velocity profiles for three equal impinging jets at
x/tp =10 and h=10 cm (corrected on the basis of fig. 4.16 )
Figure 4.18 shows the graphical presentation of turbulent intensity of this flow field.
The turbulent intensity profile as shown fluctuates with the lateral distance and has
random shape. The hot wire in this case can only gives an indication for the intensity
measurements less than or equal to 30% of the mean velocity.
H =10 cm
x/tp =10
0
1
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
y/s
2'
u
U
Figure 4.18 Axial turbulence intensity profile for three equal impinging
jets at x/tp =10 and H=10 cm.

80
At this plate distance , the impinging pressure downstream become weaker due to the
less velocity strength as shown in Fig 4.15. The total pressure starts to decrease with
an increase in lateral distance until y/s =0.6 then the pressure returns to grow up
laterally until y/s=1.1. As y/s just exceeds 1.1 sudden drops takes place to the flow
pressure and continue decreasing until reaches atmospheric. The jets spread further
before striking the plate at this distance , as a result, the shape of resultant flow field in
this region has more changes as shown in Fig. 4.19.
Figure 4.19 Flow visualization of three impinging jets at H=20 cm.
The distance between the jet exit plane and the plate is still small and the jets do not
merge with each other yet. It is clearly seen from the figure the formation of wall jets
which are moving away from the outside jets and produced by the impingement of the
two outside jets with the plate. Also it shows the formation of the upwash moving
upstream by the impact of the opposing wall jets from the outside jets (jet1 & jet 3) and
the middle jet, furthermore it shows the formation of four vortices produced by the
interaction of the upwash flow with the uptream flow. The middle jet flow is affected
more by the influence of other jets and become weaker as shown in Fig. 4.20a and Fig.
4.21a. It is clear that the middle jet velocity level at x/tp = 10 is higher than that at x/tp =20
Vertical plate

81
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
y/s
x/t=10
x/t=20
1oU
U
H=20 cm
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
y/s
x/t=10
x/t=20
1oU
U
and this may due to more entertained flow, back wash and vortices. These two figures
are modified in direction with the aid of Fig 4.19 and replotted in Fig.4.20b and
Fig.4.21b respectively to show the velocity direction in the resulting flow field as
mentioned earlier.
Figure 4.20a Axial velocity profiles for three equal impinging jets
at x/tp =10,20 and H=20 cm
Figure 4.20b Axial velocity profiles for three equal impinging jets at x/tp
=10,20 and H=20 cm (corrected on the basis of Fig. 4.19 )

82
0.1
0.2
0.3
0.4
0.5
-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
y/s
x/t=10
x/t=20
1o
V
U
H=20
cm
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
y/s
x/t=10
x/t=20
1o
V
U
Figure 4.21a Lateral velocity profiles for three equal impinging jets at
x/tp=10, 20 and H=20 cm.
Figure 4.21b Lateral velocity profiles for three equal impinging jets at x/tp=10,
20 and H=20 cm (corrected on the basis of Fig. 4.19 )
On other hand, Fig. 4.22 shows that the axial turbulent intensity in this region increases
with the axial distance but fluctuate with the increase in the lateral distance.

83
0
1
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
y/s
x/t=10
x/t=20 H=20 cm
2'
u
U
Figure 4.22 Axial intensity profiles for three equal impinging jets at x/tp =10,20
and H=20 cm.
The flow visualization pattern at this plate distance in Fig.4.23 shows two vortices exist
outside the two outer main jets close to the midway between the plate and the exit
plane. Two other vortices can also be seen near the jets exit plane. In the figure there is
a stagnation region also observed in the downstream region.
Vertical plate

84
0.1
0.2
0.3
0.4
0.5
-2.4 -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4
y/s
x/t=20
x/t=40
1oU
U
-0.5
-0.3
-0.1
0.1
0.3
0.5
-2.4 -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4
y/s
U/Uo1
x/t=20
x/t=40
1oU
U
Figure 4.24a and Fig.4.25a show the variation of the absolute mean velocity
components against the lateral distance for this flow field. It can be noticed that the
increase in the axial distance makes the jets merge more with each other and the
velocity profiles get shrink and become random. Figure 4.24b and Fig.4.25b show the
velocity corrected profiles based on the direction of the flow in this region.
at x/tp=20, 40 and H=30 cm
Figure 4.24b Axial velocity profiles for three equal impinging jets at x/tp=20, 40
and H=30 cm (corrected on the basis of Fig. 4.23 ).

85
0.1
0.2
0.3
0.4
0.5
-2.4 -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4
y/s
x/t=20
x/t=40
1o
V
U
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-2.4 -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4
y/s
x/t=20
x/t=40
1o
V
U
Figure 4.25a Lateral velocity profiles for three equal impinging jets at x/tp =20,
40 and H=30 cm.
Figure 4.25b Lateral velocity profiles for three equal impinging jets at x/tp =20,
40 and H=30 cm (corrected on the basis of Fig. 4.23 ).

86
0
1
-2.4 -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.4
y/s
x/t=20
x/t=40
H/tp=60
2'
u
U
The total pressure distribution on the vertical plate as shown in Fig.4.15 shows a high
pressure between the two outer jets and high pressure drop outside the two jets. The
pressure is high and almost constant until y/s =1, then it starts to decrease gradually
until it reaches atmospheric This explains the shape of the two wall jets and the upwash
outside the two outer main jets. Fig.4.26 shows the axial turbulence intensity profiles at
two traverse distances (x/tp=20,40). The profile is fluctuating with axial and lateral
distances as shown by the figure, the reason behind unstable velocity fluctuations
profiles is due to the fact that these measurements were taken near a high turbulence
regions which contain vortices.
Figure 4.26 Axial turbulence intensity profiles for three equal impinging jets
at x/tp =20, 40 and H=30 cm.
4. Impinging plate distance H/tp =90 (45 cm):
Figure 4.27 describes the nature of the resultant flow field behind the vertical plate at
this distance. The figure mainly shows a formation of two wall jets and two rotating
vortices in the middle plane of the resulting flow field. The two vortices are formed by

87
the interaction between the two impact wall jets which bend toward the downstream
and the two main outer jets. It is obvious from the figure that the impinging region
diverges more on the vertical plate with the increase in the plate distance. The jets
become weak and almost merge as it reaches the plate. The figure also shows large
stagnation region exist between the jets exits.
The total pressure distribution shown in Fig. 4.15 shows very low pressure level in this
region and the pressure profile looks almost straight. Also Fig.4.28 shows the static
pressure distribution of the three equal impinging jets at H=45 cm. As shown by the
figure that at the lower axial distance x=4cm the static pressure values are almost
constant, but when the axial distance increases the pressure profile changes. The
maximum value of pressure ratio is 0.2 at y/s=0.35, this value decreases with any
increase or decrease in the lateral distance along the flow field .The static pressure
profile at x/tp=56 is approximately symmetric around the center line of the middle jet.
Vertical plate

88
0.02
0.12
0.22
0.32
0.42
0.52
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2
y/s
x/tp=8
x/tp=56
2
1
1
2
O
P
U
H=45 cm
Jet 1Jet 2
Figure 4.28 Static pressure distribution across the ground three equal
strenghth jetsat H=45 cm.
In this region also velocity vectors are drawn as shown in Fig.4.29a on the basis of the
magnified picture of the flow visualization sheet of Fig.4.27. Figure 4.29b shows the
measured velocity vectors distribution at the axial locations of measurements on the
right side of this flow field region. The directions of the velocity vectors in this region
were determined with the help of Fig.4.29a.
Figure 4.29a Flow map for the right side of the visualization
pattern of three impinging jets at H=45 cm.

89
X=40 cm
X=34 cm
X= 28 cm
X=24 cm
X=23 cm
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4.0
y/s
Figure 4.29b Velocity vectors at the measuriments locations of three impinging
jets at H=45 cm.
The graphical presentation of velocity profiles of this flow field is illustrated in
Figs.4.30a-4.32 As can be seen from the figures that the mean axial velocity profile
has two symmetrical bell shapes around the two outside jets region. As the axial
distance increases the velocity ratio decreases accordingly and the bell shape of the
velocity becomes flatter due to impingement The axial turbulence intensity as shown
in Fig. 4.32 has uniform profiles for the shorter axial (distances x/tp =46,48) and
random profiles for further distances (x/tp=56,68,80) , the fluctuations are high in the
outside region compared to the inside region , it can be noted also that as the axial
distance increases the turbulent intensity decrease in the middle flow field region. On
the other hand the lateral mean velocity shown in Fig. 4.32 decreases with the increase
in lateral distance in y/s for axial locations x/tp>45 and increase with the increase in
y/s for axial locations x/tp <54.

90
0.12
0.16
0.2
0.24
0.28
0.32
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2
y/s
x/tb=46
x/tb=48
x/tb=56
x/tb=68
x/tb=80
1o
U
U
H=45 cm
-0.4
-0.32
-0.24
-0.16
-0.08
0
0.08
0.16
0.24
0.32
0.4
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2
y/s
x/tb=46
x/tb=48
x/tb=56
x/tb=68
x/tb=80
1o
U
U
H=45 cm
at x/tp =46, 48, 56, 68, 80 and H=45 cm.
Figure 4.30b Axial velocity profiles for three equal impinging jets at x/tp =46, 48,
56, 68, 80 and H=30 cm (corrected on the basis of Fig. 4.27).

91
0.12
0.16
0.2
0.24
0.28
40 45 50 55 60 65 70 75 80 85 90
x/tp
Y/S=1.0588
1.1765
1.2941
1.4118
1.6471
1.8824
1oU
V
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
y/s
u'/Uo1
x/tb=46
x/tb=48
x/tb=56
x/tb=68
x/tb=80
2'
u
U
Figure 4.31 Lateral velocity velocity profiles for three equal impinging jets
at H=45 cm.
Figure 4.32 Axial turbulence intensity profiles for three equal impinging jets
at x/tp =46, 48, 56, 68, 80 and H=45cm.

92
0.02
0.12
0.22
0.32
0.42
0.52
-2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
y/s
Uo1=Uo2=Uo3
Uo1=Uo3=0.5Uo2
Uo1=Uo2=2Uo3
2
1
1
2
O
P
U
H=45 cm
5. Unequal impinging jets at plate distance (H=45cm):
Figure 4.33 shows the pressure distribution on the vertical impinging plate at H=45 for
unequal strength three jets. For the first form of unequal jets where Uo1=Uo3=0.5Uo2,
the pressure values are high and concentrated in the middle region of the flow field
toward the strong jet. These pressure values decrease more rapidly toward the two
outside weak jets until it reaches the atmospheric pressure. The pressure distribution on
the same figure for the second form of the unequal jets where Uo1=Uo2=2Uo3,
indicate that the higher pressure values on the plate accumulate at the strong two jets
region, it decrease gradually toward the weak jet until it reach around atmospheric
value .The pressure distribution curve for equal jets under the same conditions shows
symmetrical pressure values on each side of the resultant flow field. The pressure
values are considerably low comparing to the strong jets region in the unequal jets case
.This indicate that the equal strength jets could affect each other and reduce their
momentum during interaction, consequently the pressure of the impact jets on the
impinging plate become lower.
Figure 4.33 Pressure distribution across the impinging vertical plate for
three equal and unequal jets at H=45 cm.

93
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2
y/s
x/tp=8
x/tp=56
2
1
1
2
O
P
U
H=45 cm
For the unequal impinging jets case where the two outside jets velocity strengths are
half of the middle jet Fig.4.34 shows that the static pressure distribution profiles look
approximately uniform at the two axial measuring distances. However there are two
lower pressure values at y/s =0.35 ,-0.35 around the center line of the middle jet for
x/tp=8 , these two values are corresponding to the higher two values in the static
pressure profile at x/tp=56 , the two profiles have a symmetric pressure distribution
around the centerline of the jets as shown in the figure .
Figure 4.34 Static pressure distribution across the ground horizontal plate
three unequal strenghth jets (Uo1=Uo3=50%Uo2) at H=45 cm.
Figure 4.35 shows also the static pressure distribution of the second form of the
unequal jets where the two jets have equal velocity strength (jet1 & jet2) and the third
jet has 50% strength. It can be noticed that the pressure profile at x/tp=8 looks little
straight but not symmetric due to the difference in the jets strength, the pressure values
are slightly low across the flow field and the lower static pressure value at y/s=0.35.

94
0.04
0.08
0.12
0.16
0.2
0.24
0.28
0.32
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2
y/s
x/tp=8
x/tp=56
2
1
1
2
O
P
U
H=45 cm
The figure also shows the static pressure profile of the unequal jets at axial distance
x/tp=56. It is obvious from the figure that when the lateral distance from the centerline
of the jets increases the static pressure also increases until y/s=0.5 in the strong jets
region and y/s=0.35 in the weak jets region , where it starts to decrease later with
further increase in the lateral distance until it reaches near atmospheric pressure. The
pressure distribution profile is clearly seen asymmetric around the centerline as a result
of the difference in the jets strength.
Figure 4.35 Static pressure distribution across the ground horizontal plate for
three unequal strenghth jets(Uo1=Uo2=2Uo3) at H=45 cm.
At this plate distance also of H=45 cm, the measurements of mean velocity and axial
velocity fluctuation of three unequal jets were taken, for two different exit velocity
ratios, namely Uo1=Uo3=0.5Uo2 and Uo1=Uo2=2Uo3. The resulting flow fields are
shown in Fig. 4.36 and Fig. 4.37 respectively.

95
Jet 1
Jet 3
Vertical plate
Jet 2Jet 3
Figure 4.36 Flow visualization of three un equal impinging jets (Uo1=Uo3=.5 Uo2)
at H=45 cm.
Figure 4.37 Flow visualization of three un equal impinging jets (Uo1=Uo2=2 Uo3)
at H=45 cm.
Figure 4.38 shows the mean velocity profile of the unequal jets at the axial distance
x/tp=80. The figure also includes the velocity profiles of equal jets at the same axial
measuring distance. As can be seen from the figure that the velocity profile shape of
the unequal jets where (Uo1=Uo3=0.5Uo2) behaves as if it were a single jet , the two
weak jets do not have any effect on the strong jet , they only merge with the strong jet
and then combined together to produce a nearly single jet. The velocity profile of the
other three unequal jets where (Uo1=Uo2=2Uo3) has two bell shapes, this indicates
that the middle strong jet attract the weak jet and combined together to form a single
Vertical plate
Jet 3 Jet 2 Jet 1

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