WIND TUNNEL INVESTIGATION OF JET FAN AERODYNAMICS by KUDA RONALD MUTAMA B.Sc.

194 Pages·2009·4.41 MB·English

WIND TUNNEL INVESTIGATION OF JET FAN AERODYNAMICS
by
KUDA RONALD MUTAMA
B.Sc.(Hons.), University ofLeeds (England, U.K.)
M.Sc., University ofManchester (U.M.I.S.T.), (England, U.K.)
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
in
THE FACULTY OF GRADUATE STUDIES
(Department ofMining and Mineral Process Engineering)
We accept this thesis as conforming
to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
April 1995
© Kuda R. Mutama 1995
_________________________________
_____________
In presenting this thesis in partial fulfilment of the requirements for an advanced
degree at the University of British Columbia, I agree that the Library shall make it
freely available for reference and study. I further agree that permission for extensive
copying of this thesis for scholarly purposes may be granted by the head of my
department or by his or her representatives. It is understood that copying or
publication of this thesis for financial gain shall not be allowed without my written
permission.
(Signature)
Department of MuJ tJ& -I- I’kL1\J4L JJ&
The University of British Columbia
Vancouver, Canada
Date
DE-6 (2/88)
11
ABSTRACT
This study has investigated the performance aerodynamics ofjet fans in order to identify
and understand the fundamental parameters in their use in mine and tunnel ventilation.
Despite their advantages over other ventilation methods,jet fans have not been often used
in mining due to an inability to predict performance accurately. They have been used in
longitudinal ventilation of vehicle tunnels and other installations with encouraging results
despite the fact that such systems have been designed with limiteddata.
The current studies used a wind tunnel to study jet fan ventilation. The fan was simulated
by aluminum pipes ofdifferentdiameters connected to a centrifugal blower. The aluminum
pipes were inserted at the entrance section of the wind tunnel and jet outlet velocities
ranging between 20 and 40 m/s were used to produce the flow field. In order to study
passage wall effects on the flow thejet fan was traversed from a near-wall position to the
wind tunnel axis in equal successive steps. The axial pressure development for all positions
were determined together with a detailed velocity distribution and the overall entrainment
characteristics. Both the magnitudes of the pressure drop and rise depended on the jet fan
position from the walls. Near-walljet fan positions tended to have initially larger pressure
drops and lower pressure rises than positions farther from the wall which had lower
pressure drops and higher pressure rises. The consequence of this pressure variation was
that generally at near wall positions the jet fan entrained more air into the tunnel than at
positions farther from the wall. The smaller diameter jet fan produced higher friction
losses (as much as 15 % at the wall position) than the larger diameter fan with lower
outlet velocity which had about 8 %. The flow field was found to develop rapidly with
axial distance. The jet axis velocity developed faster than that of a free jet of the same
initial velocity andrevealed thatjetfans can move air over distances greater than 70jet fan
discharge diameters and still maintain a minimum air velocity of at least 0.5 in/s. For fan
111
positioning at F < 0.4, a region of backflow was identified. The backflow fraction was
0.72 and 0.55 for the smaller and larger diameter fan respectively. The performance
parameter E of the jet fan determined from pressure and flow (eturainment) ratio
considerations QT / Q(P F)/ (P P) was found to decrease as the jet fan was
— —
moved away from the tunnel wall despite higher friction losses at near-wall positions. The
jet fan performance parameter is generally below 12 % as verified by mathematical
derivations. The larger diameter (lower velocity, Uj = 21.4 mIs) jet fan had
performance values almost twice that of the smaller diameterjet fan (Uj = 40 mIs). The
value ranged between 4.5 to 6 % for the larger diameter fan. High entrainment ratios
achieved at nearwall positions generallyimprovejet fan performance.
Theoretical equations based on momentum and energy considerations were formulated.
These derivations identified a range of flow ratios (n = 0.1 to 0.9) which can be used to
design an effectivejet fan ventilation system. For each flow ratio (n) there is an optimum
area ratio (ce) for maximum induction ofsecondary flow.
The present studies have established a procedure for jet fan performance analysis using
wind tunnel investigations and have provided useful information for jet fan ventilation
design.
iv
TABLE OF CONTENTS
ABSTRACT ii
LIST OF FIGURES vii
LIST OF SYMBOLS x
ACKNOWLEDGMENTS xii
CHAPTER ONE 1
INTRODUCTION 1
1.1 Importance ofVentilation 1
1.2 Mine Ventilation Fans 2
1.2.lMainfans 2
1.2.2 Auxiliary Fans 4
1.2.2.1 Ducted auxiliary fans 4
1.2.2.3 Ductless Fans (Jet fans) 5
1.3 Research Objectives 8
1.4 Rationale 9
1.6 Remaining Chapters 11
CHAPTER TWO 22
LITERATURE SURVEY 22
2.1 Theoretical Considerations ofIncompressible Turbulent Jets 22
2.1.2 Jets in Coflow 28
2.1.3 Round Jets with Swirl 29
2.1.5 Summary ofPrevious Work on Confined Jets 31
2.2 Jet Fan Measurements in Mine Ventilation 32
2.3 Jet Fan Investigations in Vehicle Tunnel Ventilation 39
CHAPTER THREE 53
EXPERIMENTAL PROGRAM 53
3.1 Design and Construction ofExperimental Apparatus 53
3.1.1 Wind Tunnel 53
3.1.2 Construction ofthe Wind tunnel 56
3.1.3 Wind Tunnel Instrumentation 57
3.1.4 Wind Tunnel Testing 58
3.1.4.1 Test Results 58
3.2 Jet Fan Simulation and Arrangement 60
3.3 Experimental Description ofJetFan Perfoimance Measurements 62
3.3.1 Jet Fan VelocityField Measurements 62
3.3.2 Jet Fan Pressure Measurements 63
V
CHAPTER FOUR .78
DATA REDUCTION AND ANALYSIS 78
4.1 Analysis ofPressure Results 78
4.2 Analysis of Velocity Readings 79
4.2.1 Jet Axis Velocity Decay Profile 80
4.3 Backflow Analysis and Jet Expansion Angle Determination 80
4.3.1 Jet Expansion Angle Determination 81
4.4 Entrainment Results 81
4.5 Jet Fan Performance 82
4.7 Longitudinal Velocity Fluctuations 82
4.8 Uncertainty Analysis in Measured and Derived Quantities 83
CHAPTER FIVE 85
DISCUSSION OF PRESSURE FIELD RESULTS 85
5.1 Effect ofJet Fan Position FP on Axial Pressure Development 85
5.1.1 Pressure Results for DR=0.11 Without Tunnel Coflow 85
5.1.2 Pressure Results for DR 0.17 and Uj=21.4 (Re=21165) 87
=
5.2 Comparison ofPressure Variation forTwo Differing Jet Fan
Discharge Velocities 88
5.3 Comparison of Pressure Variation for Two Jet Fan to Tunnel
Diameter Ratios 89
5.4 Axial Static Pressure Variation in the Presence ofa Strong Tunnel
Coflow 90
5.5 Pressure Ratio as a Function ofJet Fan Position (Fe) Inside the
Tunnel 91
CHAPTER SIX 103
DISCUSSION OF THE JET FAN VELOCITY FIELD DEVELOPMENT 103
6.1 Velocity Distribution for Jet Fan to Tunnel Diameter Ratio DR=O.11
and Uj=40m/s 103
6.2 Velocity Distribution for Jet Fan to Tunnel Diameterratio DR=O.17
and Uj=21.4 rn/s 105
6.3 Jet Axis Velocity Decay Inside Tunnel for a Jet Fan at Various
Positions 106
6.4 Jet Expansion Angle and Reverse Flow Phenomena 107
6.4.1 Jet Expansion HalfAngles 107
6.4.2 Description ofReverse Flow 109
6.4.3 The Quantity of Reverse Flow as Fraction ofJet Discharge
and Total Tunnel Flow 112
CHAPTER SEVEN 134
DISCUSSION OF JET FAN PERFORMANCE ANALYSIS 134
7.1 Tunnel Axis Longitudinal Turbulence Levels 134
7.2 Entrainment Rate as Function ofJet Fan Position 135
7.3 Jet Fan Performance Assessment 137
vi
CHAPTER EIGHT 143
.
THEORETICAL TREATMENT OF JET FAN PERFORMANCE USING 143
MOMENTUM AND ENERGY CONSIDERATIONS 143
8.1 Jet Fan Nozzle Energy Equation 145
8,2 Momentum Balance in the Tunnel 146
8.4 Jet Fan Performance Efficiency 148
8.5 Theoretical Estimation ofthe Backflow Fraction 149
8.6 Jet Fan Analysis from Energy Considerations 150
8.7 Analysis ofthe Performance i 155
CHAPTER NINE 163
PRACTICAL APPLICATIONS OF JET FAN WIND TUNNEL STUDIES 163
9.1 Jet Fan Application Case Study 1 163
9.2 JetFan Application Case Study 2 165
CHAPTER TEN 170
CONCLUSIONS 170
CHAPTER ELEVEN 174
RECOMMENDATIONS 174
CHAPTER TWELVE 176
CLAIMS TO ORIGINAL RESEARCH 176
REFERENCES 177
APPENDIX 181
vii
LIST OF FIGURES
Figure Page
1.1 Schematic layout ofajet fan 12
1.2 Construction ofa centrifugal fan also showing blade types 13
1.3 Construction of an axial flow fan 14
1.4 Two booster fan system in an airway 15
1.5 Typical representation offlow losses (Linsell, 1953) 16
1.6 A simplifieddiagramofamine ventilation system 17
1.7 Ducted Auxiliary ventilation fan operatingin the exhaust mode 18
1.8 Ducted auxiliary ventilation fan operating in the forcing mode 19
1.9 Jet fan ventilation in amine heading 20
1.10 illustration ofa tunnelventilated by ajetfan 21
2.1 Ajet issuing into a fluid reservoir 45
2.2 Submerged turbulentjet (notto scale) 46
2.3 Submerged freejet in a coflowing stream 47
2.4 Ductedjet showing regions ofdevelopment (not to scale) 48
2.5 Mine heading test site (Matta et al. study) 49
2.6 Mine test area with an inadquate source offresh air 50
2.7 Mine test areaventilated by ajet fan (Matta et al. studies) 51
2.8 illustration ofMcElroy’s different phases ofvelocity decay ofa 52
freely expanding turbulentjet 64
3.1 Minimum length forcontractions, without separation 65
3.2 View ofwind tunnel showing support structure 66
3.3 Wind tunnel north wall showing static pressure holes 67
3.4 Wind tunnel south wall showing hotwire access holes 68
3.5 View ofwind tunnel layout 69
3.6 View of wind tunnelfrom the axial fan discharge end 70
3.7 Arrangement ofinstrumentation 71
3.8 Axial static pressure variation for two flow settings for the
working section ofthe wind tunnel 72
3.9 Wind tunnel inletvelocity variation with time 72
3.10 Velocity profiles at Re 219560 73
=
3.11 Velocity profiles at Re 427253 74
=
3.12 Pressure drop-Reynolds numberplot for wind tunnel contraction
piece 75
3.13 Schematic ofjet fan simulation mechanism 76
3.14 Photograph ofjet fan simulation arrangement 77
5.1 Axial pressure variation (1,F 0.06 to 0.17) 94
=
5.2 Axial pressure variation (1F, 0.22 to 0.5) 94
=
viii
5.3 Axial static pressure variation on tunnel side walls (1F, 0.06 and
=
0.94) 95
5.4 Axial static pressure variation on tunnel side wall (1F, 0.11 and
0.89) 95
5.5 Axial static pressure variationon tunnel side wall (1,F 0.17 and
0.83) 96
5.6 Axial static pressure variationon tunnel side wall (Fr, = 0.22 and
0.78) 96
5.7 Axial static pressure variation on tunnel side wall (0F = 0.44 and
0.56) 97
5.8 Axial static pressure variation on both sides ofthe tunnel (0F = 0.5) 97
5.9 Axial static pressure variation vs axial distance forjet fan D7R=O.l 98
5.10 Static pressure variation ofjet fan at two different Reynolds
numbers (1,F 0.17) 99
=
5.11 Static pressure variation ofjet fan at two different Reynolds
numbers (0F 0.33) 99
=
5.12 Comparison ofpressure variation for twojet fan diameterratios 100
5.13 Pressure variation forjet fan with tunnel coflow 100
5.14 Pressure variation with tunnel coflow (U= 3 m/s) 101
5.15 Comparison ofpressure variation with and without tunnel coflow 101
5.16 Plot ofvarious pressure ratios vsjet fan position (DR = 0.11) 102
5.17 Plot ofvarious pressure ratios vsjet fan position (DR = 0.17) 102
6.1 Velocity profiles ofjet fan at various positions (DR = 0.11) 116
6.2 Velocity profiles forjet fan inside tunnel (DR = 0.17) 117
6.3 Plot ofU/Umax for different fan positions (DR = 0.11) 118
6.4 Plot ofU/Umax for different fan positions (DR = 0.17) 119
6.5 Tunnelvelocity profiles atX1/D = 45.3 (jet fan DR = 0.11) 120
6.6 Tunnelvelocity profiles atX1/D = 30.2 (jet fan DR = 0.17) 121
6.7 Jet axis velocity decay (jet fan DR = 0.17) 122
6.8 Jet axis velocity decay (jet fan DR = 0.11) 122
6.9 Jet axis velocity decay for twojetfan sizes 123
6.10 Plot ofjet expansion angle vsjet fan position (DR = 0.11) 124
6.11 Plot ofjet expansion angle vsjetfan position (DR = 0.17) 124
6.12 Tunnel cross sectional backflow velocity profile forjet fan at
-
(1X/D 18.2) 125
=
6.13 Plot ofbackflow velocity profile vs distance across tunnel 126
6.14 Width ofbackflow atvariousjet fan positions (DR = 0.11) 127
6.15 Width ofbackflow at variousjet fan positions (DR = 0.17) 127
6.16 Backflow width forjet fan with tunnel coflow velocity of0.5 m/s 128
6.17(a) Flow visualizationphotographs (DR = 0.11) 129
6.17(b) Flow visualizationphotographs (DR = 0.17) 130
6.18 Extent ofbackflow length vsjet fan position (DR = 0.11) 131
ix
6.19 Extent ofbackflow length vsjet fan position (DR = 0.17) 131
6.20 QR/QT vs X1/D forjetfan diameterratios DR = 0.11 and 0.17 132
6.21 Plot ofbackflow fraction vsjet fan position 133
6.22 Backflow fraction and vsjet fan position 133
Q1R/Q QR/QT
7.1 Tunnel centreline longitudinal turbulence levels 140
7.2 Flow ratio vsjet fan position inside windtunnel (DR = 0.11) 141
7.3 Flow ratio vsjetfan position inside wind tunnel ((DR = 0.17) 141
7.4 Jet fan performance vsposition (DR = 0.11) 142
7.5 Jet fan performance vs position (DR = 0.17) 142
8.1 Schematic description ofjet fan tunnel system 158
-
8.2 Velocity decay ofan axisynimetric freejet showing mixing concept 159
8.3 Figure 8.3 Plot oftheoretical performance vs flow ratio n 160
8.4 Figure 8.4 Plot oftheoretical performance vs flow ratio (n) for
variousjet fan positions (friction loss factors) 160
8.5 Optimum flow ratio andperformancevs optimum pressure ratio 161
8.6 Figure 8.6 Friction loss ç vsjet fan position F 161
8.7 Figure 8.7 Performance vs area ratio forvarious flow ratio n 162
8.8 Figure 8.8 Flow ratio n vs optimum arearatio 162
9.1 Figure 9.1 Example ofjetfan used in through flow to increase
167
airflow in other mine ventilation districts
9.2 Figure 9.2 Jet fan used in a closed heading with curtain to reduce
168
return airentrainment
169
Figure 9.3 illustration offlow ratio vs total flow for a 5 and 10
m3/sjet fan
169
Figure 9.4 Jet fan fitted with an entrainment tube as in an ejector