Fluid Mechanics for Civil Engineers: SI edition

369 Pages·1971·11.963 MB·\369

by  N.B. Webber (Author)

FLUID MECHANICS FOR
CIVIL ENGINEERS

FLUID MECHANICS
FOR CIVIL ENGINEERS
S.I. Edition
N. B. WEBBER B.Sc.(Eng.), M I C E.,
M.Am.Soc.C.E., M.I.W.E., M.I.Struct.E.
,
Formerly Senior Lecturer in Civil Engineering University of Southampton
CRC Press
(eve
Taylor & Francis Group
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© 1971 N.B. Webber
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ISBN-13: 978-0-412-10600-2 (pbk)
ISBN-13: 978-1-138-43398-4 (hbk)
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Contents
page
Preface to S.I. Edition viii
Preface to Imperial Edition ix
List of Principal Symbols with Derived Dimensions xii
Properties of Fluids xv
Conversion Factors and Useful Constants xvi
1 Historical Note 1
2 Properties of Fluids 6
1. General Description 6
2. Density 6
3. Specific Weight 6
4. Specific Gravity 7
5. Bulk Modulus 7
6. Ideal Fluid 7
7. Viscosity 7
8. Surface Tension and Capillarity 9
9. Vapour Pressure 10
10. Atmospheric Pressure 10
3 Hydrostatic Pressure and Buoyancy 12
1. Hydrostatics 12
2. Pressure Intensity 12
3. Pressure Measurement 13
4. Pressure Force on a Submerged Surface 16
5. Buoyancy 21
6. Stability of Floating Bodies 21
4 Basic Concepts of Fluid Motion 25
1. Introduction 25
2. Types of Flow 26
3. Stream Lines 29
4. Continuity Equation 30
5. Bernoulli Equation 31
6. Applications of Bernoulli Equation 33
v
CONTENTS
7. Momentum Equation 40
8. Applications of Momentum Equation 41
9. Flow in a Curved Path 44
10. Flow Nets 50
11. Behaviour of a Real Fluid 53
12. Dimensional Considerations 68
5 Analysis of Pipe Flow 76
1. Introduction 76
2. Laminar Flow - Poiseuille Equation 76
3. Turbulent Flow - Darcy-Weisbach Formula 78
4. The Contribution of Osborne Reynolds 79
5. Experimental Investigations on Friction Losses in Turbulent Flow 83
6. Semi-empirical Theory of Pipe Resistance 86
7. Colebrook and White Transition Formula 95
8. Empirical Formulae 99
9. Deterioration of Pipes 103
10. Non-circular Pipes and Conduits 104
11. Minor Losses in Pipes 104
12. Summary of Formulae 108
6 Pipelines and Pipe Systems 110
1. Hydraulic and Energy Gradients 110
2. Power Transmission 111
3. Discharge under Varying Head 113
4. Simple Pipe Systems 114
5. Distribution Mains 119
6. Transient Behaviour 129
7 Uniform Flow in Channels 143
1. Introduction 143
2. Laminar Flow 144
3. Fundamental Relationships 146
4. Empirical Formulae 151
5. Best Hydraulic Section 158
6. Enclosed Conduits 161
7. Scouring and Silting 164
8 Non-uniform Flow in Channels 168
1. Introduction 168
2. Specific Energy and Critical Depth 168
3. Transition through Critical Depth 177
4. General Equation of Gradually Varied Flow 185
5. Classification of Surface Profiles 187
6. Control Points 191
7. Outlining of Surface Profiles 193
8. Profile Evaluation 195
9. Bridge Piers 202
10. Translatory Waves in Channels 204
vi
CONTENTS
9 Hydraulic Structures 211
1. Introduction 211
2. Sluices and Gates 211
3. Sharp-crested Weirs 214
4. Solid Weirs 221
5. Special Types of Weir 224
6. Throated Flumes 226
7. Spillways 231
8. Inflow-outflow Relationship at a Reservoir 246
10 Pumps and Turbines 252
1. Introduction 252
2. Head 253
3. Synchronous Speed 256
4. Types of Pump 257
5. Types of Turbine 263
6. Elementary Theory 272
7. Performance 279
8. Specific Speed 287
9. Cavitation Considerations 292
10. Design of a Pumping Main 295
11 Hydraulic Models 297
1. Introduction 297
2. Hydraulic Similarity 299
3. Conformance with Similarity Laws 302
4. Types of Model Investigation 307
5. Measuring Instruments and Techniques 322
Appendix 324
General Publications Relevant to Hydraulic Engineering 324
Name Index 327
Subject Index 330
vii
Preface to S.I. Edition
The decision by Britain and many other countries to adopt the S.I.
system of units has made it desirable to publish an edition using these
units.
The S.I. system (Systeme International d’Unites) is a rationalized
selection of metric units, whose principal merit lies in the fact that it
comprises no more than six basic units. This is in contrast to the non­
coherent English system with its multiplicity of units and a convention
that is not always logical or consistent. Civil engineering hydraulics
makes use of a wide range of quantities and units, and in the process of
conversion the author has been impressed by the inherent simplicity of
the new system and the economy of working which results.
The opportunity has been taken to up-date and revise the text where
this has been considered necessary or desirable.
Again, the author is considerably indebted to Dr T. L. Shaw of
Bristol University for his encouragement in the task and for his subse­
quent critical scrutiny of the manuscript. The advice and co-operation
of the publishers is also gratefully acknowledged.
N. B. WEBBER
The University,
Southampton,
July, 1971
NOTE ON REPRINT
In reprinting, the opportunity has been taken to introduce certain
desirable amendments and to bring up-to-date the references for further
reading.
Preface to Imperial Edition
A glance at the list of textbooks on the subject of fluid mechanics (see
appendix) would appear to indicate no lack of suitable material. But the
treatment is almost invariably very broad and, with the degree of
specialisation unavoidable in our engineering curricula today, there does
seem a need for a book which would be concerned primarily with the
civil engineering aspect. This was the author’s aim in writing the
present book, and the experience of seven years of undergraduate teaching
preceded by more than ten years of engineering practice has been drawn
upon in its compilation.
The subject matter embraces the field normally covered in a complete
hydraulics course at undergraduate or comparable level. It provides the
groundwork that is necessary before proceeding to the more specialised
studies of hydraulic engineering. Without detracting from a considera­
tion of the fundamentals, an attempt has been made to bridge the gap,
still too wide, between theory and practice. In this way it is hoped that
the book will also appeal to practising engineers, for there is now an
increasing awareness of the value of the more soundly based and
rational approach afforded by modem fluid mechanics.
Fluid mechanics, as the name implies, is a branch of applied
mechanics. Its foundations are the laws of motion enunciated by
Newton. The concepts are rational, being based on sound physical
reasoning, mathematics, and the results of experiments. By analytical
means it seeks to derive equations that are of a general nature, repre­
senting these where possible in dimensionless form. This is in contrast
with empirical hydraulics where, because of the limited experimental
data on which formulae have been established, certain reservations must
be placed on their range of application.
The text commences with a short historical note which serves as an
introductory background. This is followed by four chapters concerned
primarily with the presentation of fundamental principles, embracing
both fluid statics and dynamics. Topics include the phenomena associ­
ated with turbulent flow and a rational theory for pipe resistance. The
remaining chapters deal with the practical application of these principles.
By devoting the last chapter to a consideration of model testing recogni-