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namely- increasing U/V reduces the proportion of the jetted sediment that lands in the lee slope (modes Ml and M2) and increases the proportion that is carried to the downstream crest (M6 and M7) . The M3 and M4 trajectories are changed only slightly perhaps because this model coincides with the timeaveraged reattachment point. We say this because the ratio of separation length to bedform height is often said to be about 3 (Nezu & Nakagawa, 1991), corresponding to the M4 model (ie at 0.15m). The sedimentation rate onto each site expressed as a percentage of total sedimentation for these runs has been discussed previously - As a correlation basis for practical applications, our data sets were fitted with the exponential function S=bXm where S is the sedimentation rate and X is the distance downstream. Figure 23 shows best fit values of exponent (m) and intercept (Lnb) plotted against U/V. They vary nearly linearly with U/V, giving a good fit at high U/V values. This implies that the local sedimentation rate at any U/V can be expressed as a function of U/V and X. From the gradients of the two lines in figure 23 we have as correlation fit to our data: iJ rrj where S T is the total sedimentation rate of the jetted load, ie the bedload transport rate. There is no obvious significance to this formula, but at least it provides an approximation for 3-15
likely distributions. 4 DISCUSSION For any given flow rate over a flat bed or over a bedform carrying a wide particle size range we can divide the total sediment transport into bedload, suspended load or wash load; Gyr (1983) . Flow separation causes essential differences in the bedform system, mainly by producing a distinctively inhomogeneous vorticity distribution which is available to interact with the sediment. Our experiments were designed to highlight visually this behaviour and to characterise important suspension mechanisms around such bedforms. Although direct visualisation made for tedious retrieval of quantitative information (25,000 footprints from 2500 trajectories), it nevertheless provided an opportunity to identify a new phenomenon in sandwave transport which is reported in chapter 4. The use of fixed bedforms and model particles facilitated independent observation of sediment suspension from different areas of the bedform. In closing this section we define an "interactive fraction" for sediment suspension from jetted load and consider how this concept may be utilised for field application. 3-16
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FLUID-PARTICLE TRANSPORT DYNAMICS O
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SYNOPSIS The local dynamics of sand
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TABLE OF CONTENTS LIST OF FIGURES C
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CHAPTER 3: JETTING EXPERIMENTS Summ
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2 Numerical scheme 6-5 3 Results 6-
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LIST OF FIGURES Chapter 1 Figure 1.
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U=830mm/s. Figure 16. Thomas et al
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in the boundary layer. a) The forma
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Chapter 3 Figure 1. After Alien (19
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at various values of U/V from 2.7 t
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y Coanda-flapping of the free shear
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of a sandwave crest in the estuary
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Figure 7h-i. The temporal fluctuati
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inclined downwards whereas the time
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starting position (X,Y) at zero ini
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d Sand grain diameter (m) Fi Number
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G Vortex core growth rate (tn/s) ki
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1 INTRODUCTION Sand forms the botto
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where U is the depth-averaged veloc
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The wavelengths of dunes primarily
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detached and then confined within a
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The vortex radius rn and apparent w
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Recent work by Nezu & Nakagawa (199
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found in the outer streaks. 4 MODEL
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(1987), for example, modelled gas-s
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Profiles of shear stress and turbul
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6ft v "' ' Re In the limit of large
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that the particle radius was much s
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and travels downstream at speed }*U
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capture by transient large eddies s
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Chapter 1 Figure 3. Alien (1984). L
Page 63 and 64: Chapter 1 10 8 e 4 I 08 •- 02 Yal
Page 65 and 66: Chapter 1 bw speed fluid Figure 11.
Page 67 and 68: Chapter 1 Figure 16. Thomas et al (
Page 69 and 70: Chapter 1 StCMl STRESS SCALE « K /
Page 71 and 72: Chapter 1 Haiht Vdodty Figure 22. S
Page 73 and 74: Chapter 1 Time = 1.2 2.4 ' ' :•
Page 75 and 76: 1 INTRODUCTION AND DESIGN CONSIDERA
Page 77 and 78: Initial costing for a flume of the
Page 79 and 80: flanges and a maximum flow rate of
Page 81 and 82: could be wound above or below the l
Page 83 and 84: 4 EXPERIMENTAL SETUP AND METHODS He
Page 85 and 86: 4.2 Flow visualisation and model pa
Page 87 and 88: any divergence from the beam and to
Page 89 and 90: even flow over 0.45m width and up t
Page 91 and 92: Chapter 2 Opt 1 h(m) 0.01 Max D(m)
Page 93 and 94: Chapter 2 Part of side section Putt
Page 95 and 96: Chapter 2 Suction tank Bypass Disch
Page 97 and 98: Chapter 2 QUncorrectedflow £ Corre
Page 99 and 100: Chapter 2 60 r 501 40? 30r 20 r lOr
Page 101 and 102: 1_ INTRODUCTION The main features o
Page 103 and 104: 2 EXPERIMENTAL METHODS A detailed d
Page 105 and 106: the relationship is then simply ^ -
Page 107 and 108: number about 0.14. They were taken
Page 109 and 110: along the stoss slope. Figures 8 an
Page 111 and 112: 3.3a) Jetting trajectories when U/V
Page 113: errors increase substantially due t
Page 117 and 118: Our suggestion here is akin to that
Page 119 and 120: not accommodate the differing migra
Page 121 and 122: considered by proponents of numeric
Page 123 and 124: Chapter 3 C,;: Figure 3a-j. The pla
Page 125 and 126: Q CO 23 Figure 6. Distribution of p
Page 127 and 128: Chapter 3 X(cm) 1 2 3 4 5 6 7 8 9 1
Page 129 and 130: Chapter 3 U(m/s) V(m/s) U/V M1+M2 M
Page 131 and 132: O I r+ 21 CO 2 5 8 11 14 17 20 23 >
Page 133 and 134: 8 11 14 17 20 23 25 + Position Figu
Page 135 and 136: Chapter 3 U/V= B5.7 Q9.3 BlO.7^12.8
Page 137 and 138: Chapter 3 Band 1 2 3 4 U(m/s) 0.2 0
Page 139 and 140: 1 INTRODUCTION In chapter 3 we cons
Page 141 and 142: velocity for a maximum of 40% of th
Page 143 and 144: layer vortices extending over the d
Page 145 and 146: 2.2 Methods for measuring Coanda-fl
Page 147 and 148: Section 3.4 considers suspension fr
Page 149 and 150: This same flow structure has also b
Page 151 and 152: 3.2b) Effect of varying inter-crest
Page 153 and 154: those with fall speed 0.060m/s for
Page 155 and 156: 3.4 Particle capture from stoss slo
Page 157 and 158: are discussed in the context of est
Page 159 and 160: jetted grains settling to the lee s
Page 161 and 162: Chapter 4 ENTRAINED FLOW Figure 1.
Page 163 and 164: Figure 3a-j. The plates show partic
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Chapter 4 Percentage occurrence •
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Chapter 4 Interval (s) 60 80 100 12
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Chapter 4 0.024m Conc=8% Figure 12.
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Chapter 4 Figure 16. A cloud of par
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1 INTRODUCTION We use a Rankine vor
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effective particle fall speed in th
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particle velocity Vx=0. The initial
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the vortex axis. Vortex circulation
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dimensional fall times T^ for diffe
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horizontal component lift force (fi
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corresponds to the trajectory trave
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stepping the calculation in VT . Do
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averaged exclusion of the coherent
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C from figure 11 (ie 2.2) then we h
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PflRTICLE DENSITY=1000.000 Kg/n3 LI
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Chapter 5 ft) J k I Figure 4. Varyi
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Chapter 5 Relative Fall Time va Sta
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Chapter 5 Figure 7a. Trajectories o
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Chapter 5 Velocity X —Inertia X L
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Chapter 5 Velocity X —Velocity Y
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Chapter 5 Velocity Y Inertia Y Lift
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Chapter 5 DENSITY PARTICLE=2850.000
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Chapter 5 Rad = 0.006 Rad=0.003 Rad
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Chapter 5 H3 Y=0 Oy=i m Y=2 D-y=3
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CHAPTER 6: NUMERICAL SIMULATION OF
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next. If we now adopt the classical
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st = (4) Where p p was the particle
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3 RESULTS 3.1 Specified 6 and V Fig
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the blue squares to double loops an
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A0fl0 = 1.25V-0.33G-0.005 (7) and f
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Conversely, the upper line of the p
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equations. Such a discrete vortex m
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Figure 1. Schematic of the shear la
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Chapter 6 J G H K M Figure 3. Seven
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Chapter 6 1 T V=0.161 0.1 -- V41185
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Chapter 6 - DataV=0.0335, G=0.01
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CHAPTER 7: RECAPITULATION AND RECOM
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were shown to compare well with pre
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We have shown Coanda-flapping makes
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figure 5, was critically dependant
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stoss slope suspension studies of c
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Figure la-g. The seven trajectory m
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Chapter 7
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Chapter 7 0.0351 0.03 " 03 0.025 0.
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Flow 16 (1) pp 19-34. Bernal LP (19
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Mechanics of Sediment Transport. Is
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turbulence near a smooth wall in a
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moderate Reynolds number shear laye
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Spalding (1961). A single formula f
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USA. 1-12
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APPENDIX 1: BOUNDARY LAYER STUDIES
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(1967) used hydrogen bubble visuali
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The burst-sweep dynamics study of U
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Horseshoe vortex Vortex filament Ho
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APPENDIX 2: FAST9003.HR(RW)/NHT - P
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of the vorticity shed into the near
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transport dynamics of multiphase fl
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APPENDIX 3: FUNDAMENTAL NAVIER-STOK
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APPENDIX 4: CLOSURE METHODS 1 ZERO
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where cr k and CD are empirical con
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K = CDe^ 2 p 2 \U2 -U1 \=e 1e 2 c (
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APPENDIX 6: K-e MODEL OF JOHNS ET A
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They then defined a hydrodynamic co
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with respect to the rest of the vor
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The vorticity equation can be split
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around the crest and the motion of
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micrometers, with mean of 80 microm
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i——COMPARISON WITH PREVIOUS WOR
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width speed (metres) ^(cm/s) 11 Fig
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U (33) = 1.16ms-' Depth = 2.65 m Fi
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APPENDIX 9 : DERIVATION OF FORCES O
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APPENDIX 10 : MODEL CODE FOR CALCUL
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APPENDIX 11: MODEL CODE FOR GROWING
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105 if (scancode .eq. 57) stop GOTO
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