Measurements within self-aerated flow on a large spillway

388 Pages·2014·20.55 MB·English

by  Paul Cain

MEASUREMENTS WITHIN SELF-AERATED FLOW
ON A LARGE SPILLWAY
A thesis presented for the degree of
Doctor of Philosophy in Civil Engineering
at the University of Canterbury,
Christchurch, New Zealand.
by
PAUL CAIN
April 1978
FRONTISPIECE Self-Aerated Flow on the Spillway of Aviemore Dam, Waitaki River, New Zealand.
Spillway gates open 600 mm except central gate open 300 mm.
ENGINEERING
Lt&RAI\Y
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ABSTRACT
Instruments were developed and were used to obtain measurements
of the most important flow parameters within self-aerated flows on the
spillway of Aviemore dam.
Compressibility effects within self-aerated flows are examined.
It is shown that Mach numbers as large as 2 will occur in localised
aerated regions on large structures.
A probe was developed which measured stagnation pressure and air
concentration. The compressible nature of self-aerated flows is taken
into consideration in formulating a relationship between these measurements
and the velocity of the water. This expression is found to overestimate
the velocity by about 7% over a wide range of flow conditions.
A velocity probe was also developed, based on a cross-correlation
technique. This latter probe was the more successful and is recommended
for future measurements within self-aerated flows.
Profiles of stagnation pressure, air concentration and velocity
were measured at each of five positions down the spillway for each of two
discharges. These are.the most comprehensive and detailed measurements
yet obtained on a large structure.
The regions of non-aerated, partially aerated and fully aerated
flow down a spillway are distinguished. A dimensional analysis is used
to indicate the important variables effecting the distribution of air
downstream of the point of inception. This forms the basis for plotting
the measurements from Aviemore plus the available measurements from
laboratory flumes.
The shear stress on the spillway surface at Aviemore is calculated
from the measurements.
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ACKNOWLEDGEMENTS
The writer gratefully acknowledges the opportunity to undertake
research within the Civil Engineering Department, University of Canterbury,
and expresses his sincere thanks to the following persons:
Professor I. R. Wood who supervised this research, providing
inspiration, guidance and encouragement.
Mr. A. Stokes who constructed much of the test equipment and
assisted with the field tests.
Messrs. C. Rowe and D. Chambers of DAVCO who developed the
electronics for the field tests. Mr. c. Rowe also provided invaluable
assistance throughout all phases of the research.
Mr. P. J. Robinson who constructed electrical equipment and
assisted with the field tests.
Messrs. K. D. McCool, L. Newbury and G. Symes of the New Zealand
Electricity Department for their co-operation that made the field tests
possible. Also, the staff at Aviemore who assisted with the measurements.
Messrs. s. M. J. Smith and J. Crawford of the Ministry of Works
and Development who provided the equipment for access onto the spillway.
Also, Dr. R. J. Keller who assisted with the field tests.
w.
Mr. K. Kennedy of the Electrical Engineering Department who
generously assisted with data analysis.
i i;
Those University staff, technicians and post-graduate students,
too numerous to mention individually, whose interest and help is
appreciated.
My friends, family and Lynnie for their moral support.
This study was financially supported by the University Grants
Committee.
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CONTENTS
ABSTRACT i
ACKNOWLEDGEMENTS ii
CONTENTS iv
LIST OF SYMBOLS ix
CHAPTER 1 - INTRODUCTION 1
1.1 Summary 1
1.2 Introduction 1
1.3 Flow Description 1
1.4 Literature Survey 9
1.5 Existing Test Facilities at Aviemore 13
1.6 Test Conditions 16
1.7 Initial Instrument and Test Design
Considerations 16
CHAPTER 2 - VELOCITY PREDICTION FROM AIR CONCENTRATION
AND STAGNATION PRESSURE. 20.
2.1 Summary 20
2.2 Introduction 20
2.3 Flow Relationships 21
2.4 Velocity Prediction in Aerated Flows 27
2.5 Pressure Scales 40
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CHAPTER 3 - AIR CONCENTRATION MEASUREMENT
41
3.1 Swnmary 41
3.2 Introduction 41
3.3 Resistance Method of Air Concentration
Measurement 42
3.4 Measurement of Resistance 47
3.5 Probe Design 48
3.6 Input-Output Relationship 55
3.7 Choice of Reference Resistance 70
3.8 Partially Submerged Electrodes 72
CHAPTER 4 - STAGNATION PRESSURE MEASUREMENT 74
4.1 Summary 74
4.2 Probe Design Criteria 74
4.3 Pressure Transducer Response .76
4.4 Theoretical Analysis of Dynamic Response 79
4.5 Test Methods for Determining Dynamic Response
of Pressure Transducers Plus Pressure
Transducers and Inlet Tubes 84
4. 6 Pressure Transducer Selection 90
4.7 Pressure Inlet Tube used in Initial Field Tests 95
4.8 Pressure Inlet Tube Used in Final Field Tests 102
CHAPTER 5 - BUBBLE AND VELOCITY PROBES 112
5.1 Summary 112
5.2 Bubble Probe 112
5.3 Velocity Probe 118
5.4 Analysis of Aviemore Velocity Data 129
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Page
CHAPTER 6 - LABORATORY CALIBRATION TESTS 133
6.1 Summary 133
6.2 Introduction 133
6.3 A Flow Simulator 134
6.4 B Flow Simulator 137
6.5 Calibration Tests 143
CHAPTER 7 - FIELD TEST EQUIPMENT 160
7.1 Summary 160
7.2 Introduction 160
7.3 Spillway Instrument Assembly 160
7.4 Electrical System 168
7.5 Recording Equipment 174
CHAPTER 8 INITIAL FIELD TESTS 177
8.1 Summary 177
8.2 Introduction 177
8.3 Test Program 178
8.4 Results 179
8.5 Major Faults 180
8.6 Modifications for Final Field Tests 181
CHAPTER 9 - FINAL FIELD TESTS 182
9.1 Summary 182
9.2 Description 182
9.3 Mains Frequency Variations 186
9.4 Spillway Gate Opening Variations 191
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Page
CHAPTER 10 - RESUL'I'S 195
10.1 Summary 195
10.2 Introduction 195
10.3 Data Reduction 196
10.4 Velocity Prediction 233
10.5 Adjusted Air Concentration Profiles 261
CHAPTER 11 - DISCUSSION OF RESULTS 274
11.1 Summary 274
11.2 The Different Flow Regions 274
11.3 Non-Aerated Region of Flow 276
11.4 The Region Downstream of the Point of
Inception 281
11.5 Partially Aerated Region 287
11.6 Fully Aerated Region 305
CHAPTER 12 SUMMARY AND CONCLUSIONS 313
12.1 Summary 313
12.2 Instrumentation Appraisal and Conclusions 313
12.3 Summary of Results 319
12.4 Proposals for Future Research 320
REFERENCES 322
APPENDIX A - PHOTOGRAPHS OF FLOW SURFACE A.l
APPENDIX B - DERIVATION OF VELOCITY RELATIONSHIPS IN AIR-WATER
MIXTURES B.l
APPENDIX C - RANGE OF FLOW PARAMETERS C.l
APPENDIX D - FREQUENCY RESPONSE OF ELECTRODES 0.1
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APPENDIX E - ELECTRICAL SPECIFICATIONS E.l
APPENDIX F - SOURCE FREQUENCY F.l
APPENDIX G - INLET TUBE DESIGN FOR OPTIMUM DYNAMIC RESPONSE G.l
APPENDIX H - PRESSURE WAVE ANALYSIS H.l
APPENDIX I - VELOCITY INSTRUMENT CIRCUIT DIAGRAM I.l
APPENDIX J - DESCRIPTION OF EAI 590 HYBRID COMPUTER J.l
APPENDIX K - CROSS-CORRELATION PROGRAM K.l
APPENDIX L - GAMMA RADIATION ABSORPTION L.l
APPENDIX M - MAINS FREQUENCY VARIATIONS M.l
APPENDIX N - DATA ARRAYS N.l
APPENDIX P - INTERMITTENCY PARAMETER, PLOTS P.l