Coherent Flow Structures at Earth's Surface

Coherent Flow Structures at Earth’s Surface......Page 3
Contents......Page 7
List of Contributors......Page 9
Preface......Page 13
About the Companion Website......Page 15
1.1 Introduction......Page 17
1.2 From random turbulence to coherent flow structures......Page 18
1.3 Coherent flow structures in low Reynolds-number flows over smooth boundaries......Page 20
1.4 Large-scale, high Reynolds-number coherent flow structures......Page 23
1.5 Does scale matter?......Page 26
1.6 What is the difference between the mean flow and CFS?......Page 27
1.7 Coherent flow structures within geophysical flows: future research needs......Page 28
References......Page 30
2.1 Introduction......Page 33
2.2.2 Hairpins and hairpin vortex packets......Page 34
2.3 Interactions of eddies on different scales......Page 37
2.5 Conclusions......Page 38
References......Page 39
3.1 Introduction......Page 41
3.2 Experiments......Page 43
3.3.1 Instantaneous velocity fields......Page 46
3.3.2 Single-point statistics......Page 48
3.3.3 Two-point velocity correlations......Page 50
3.5 Conclusions......Page 55
References......Page 56
4 Coherent Flow Structures in the Pore Spaces of Permeable Beds underlying a Unidirectional Turbulent Boundary Layer: A Review and some New Experimental Results......Page 59
4.2 Flow across a permeable boundary layer: background......Page 60
4.3.2 Turbulence structure in the freeflow......Page 62
4.4.1 Conceptual models......Page 65
4.4.2 Experimental observations of coherent flow structures in the transition layer and their evolution......Page 66
4.4.3 Turbulence penetration into the bed: preliminary quantification using a novel refractive index matching (RIM) experimental approach......Page 71
4.6 Summary and challenges for future work......Page 74
Notation......Page 75
References......Page 76
5.1 Introduction to Kelvin–Helmholtz and Holmboe instabilities......Page 79
5.2 One-sidedness......Page 81
5.3 Application of the Taylor–Goldstein equation to asymmetric profiles......Page 82
5.4 Mixing......Page 83
5.5 Field observations......Page 85
References......Page 86
6.1 Introduction......Page 89
6.3 Scope......Page 91
6.4.1 The Turbulent flux budget......Page 92
6.4.2 Gradient-diffusion closure for the triple moment......Page 95
6.4.3 Linking the triple moment to the ejection-sweep cycle......Page 96
6.4.4 Scalar variance......Page 97
6.4.5 Scalar spectra......Page 100
6.4.6 Scalar co-spectra......Page 102
6.4.7 Scalar fluxes, fine-scale turbulence and ramp patterns......Page 104
6.6 Acknowledgements......Page 107
References......Page 108
7.1 Introduction......Page 113
7.2.1 SLTEST experimental setup......Page 115
7.2.2 Assessing the thermal stability regime......Page 116
7.3.1 Experimental setup......Page 117
7.4 Results......Page 118
7.4.1 A qualitative picture of large scale structures in the wall region......Page 119
7.4.3 A quantitative picture of ramplike structures......Page 120
References......Page 123
8 Critical Reflections on the Coherent Flow Structures Paradigm in Aeolian Geomorphology......Page 127
8.1 Introduction......Page 128
8.2.1 Topographically unconstrained......Page 129
8.2.2 Topographically forced......Page 130
8.3.1 Wind unsteadiness and quadrant signatures in aeolian transport......Page 131
8.3.2 Aeolian streamers as manifestations of coherent flow structures......Page 132
8.3.3 Flow structures around small obstructions......Page 135
8.4.1 Macro-scale structures......Page 138
8.4.2 Signatures of turbulence in flow over dunes......Page 141
8.5 Discussion......Page 142
8.6 Summary and conclusions......Page 145
References......Page 146
9.1.1 Canopy geometry......Page 151
9.2.1 Stem-scale coherent structures......Page 152
9.2.2 Coherent structures at a single canopy edge......Page 153
9.2.3 Canopies with two flow-parallel edges......Page 155
9.2.4 Circular patch......Page 157
References......Page 161
10.1 Introduction......Page 165
10.2.1 Field observations......Page 166
10.2.2 Large-eddy simulation......Page 167
10.3 Buoyancy forcing......Page 169
10.3.1 Similarity of momentum and scalar transport......Page 171
10.3.2 Influence of boundary-layer scale circulations......Page 172
10.4 Summary and conclusions......Page 174
References......Page 175
11.1 Introduction......Page 177
11.2.1 Wind tunnel......Page 178
11.2.3 Stereoscopic PIV setup......Page 179
11.3.1 Analysis of instantaneous velocity fields......Page 180
11.3.2 One-point statistics......Page 181
11.3.3 Two-point statistics......Page 182
11.3.4 Length scales of turbulent structures......Page 183
11.3.5 Qualitative evidence of very-large scale structures......Page 185
11.3.6 Conditional averaged velocity fields......Page 186
11.4 Discussion and conclusion......Page 187
References......Page 189
12.1 Introduction......Page 191
12.2 Method of LES......Page 194
12.3.1 Flow over smooth, rough and permeable beds......Page 195
12.3.2 Flow through vegetation......Page 200
12.3.3 Flow over dunes......Page 205
12.4 Conclusions......Page 210
References......Page 211
13.1 Introduction......Page 215
13.2.2 Flow measurement......Page 217
13.3 Methodology......Page 219
13.3.1 Velocity measurements......Page 220
13.4 Results......Page 221
13.4.2 The flow contained within each structure......Page 224
13.4.3 Linking trajectories of flow to flow structures......Page 225
13.5 Discussion......Page 227
References......Page 228
14.1.1 The COHSTREX project......Page 231
14.1.2 The cool skin effect and infrared remote sensing......Page 232
14.2 Stratified flow experiment......Page 233
14.2.1 Infrared signatures of thermal variability......Page 234
14.2.2 Acoustic imaging of boils......Page 235
14.2.3 Model for vertical boil propagation......Page 237
14.3 Unstratified flow experiment: thermal imaging......Page 239
14.3.1 Small-scale surface velocity......Page 241
14.3.2 Large-scale river flow......Page 244
14.4 Summary......Page 245
References......Page 246
15.1 Introduction......Page 247
15.2.2 Field campaign......Page 248
15.3.3 Turbulence parameters......Page 249
15.4.2 Hydrodynamic and sedimentological characteristics......Page 250
15.4.5 Flow structure during cloud observation......Page 251
15.4.6 Coherent flow and SSC structure variability on a tidal cycle......Page 252
15.5.1 The origin of the suspension clouds......Page 254
15.5.2 Hydrodynamic threshold for the occurrence of suspension clouds......Page 255
15.6 Conclusions......Page 256
References......Page 257
16.1 Introduction......Page 259
16.2.1 Field studies of pool hydrodynamics......Page 260
16.2.2 Flume and numerical experiments......Page 263
16.3.2 Instrumentation......Page 264
16.3.4 Experimental runs......Page 265
16.4.1 Distribution of flow and turbulence......Page 266
16.4.2 Large-scale flow structures......Page 268
16.4.3 Sensitivity to channel geometry......Page 270
16.5 Discussion and conclusion......Page 272
References......Page 274
17.1 Introduction and research context......Page 277
17.2.1 Data sampling......Page 279
17.2.2 Data analysis......Page 281
17.3.1 Time series characteristics......Page 284
17.3.2 Flow pulsation detection......Page 285
17.3.3 Flow pulsation scalings......Page 286
17.4 Discussion......Page 287
17.5 Implications and conclusions......Page 288
References......Page 289
18.1 Introduction......Page 291
18.2.2 Water-worked gravel bed......Page 294
18.2.3 Particle image velocimetry (PIV) flow measurement......Page 295
18.3.1 Streamwise flow velocities......Page 296
18.3.2 Secondary flow velocities......Page 297
18.3.3 Turbulence......Page 299
18.4.1 Secondary flow circulation cells......Page 300
18.5 Conclusions......Page 303
References......Page 304
19.1 Introduction......Page 305
19.2 Grain-flow interaction: recent developments......Page 307
19.3 Fluctuating fluid forces......Page 309
19.4 Particle dislodgement paradox......Page 311
19.5 Resolution of the particle dislodgement paradox......Page 312
19.6 Analytical formulation......Page 314
19.7.1 Fluctuating force measurements on an instrumented immobile grain......Page 315
19.7.2 Measurements of mobile grain entrainment......Page 317
19.8 Thoughts on coherent structures and grain entrainment......Page 318
19.9 Some additional thoughts on the impulse concept and particle entrainment......Page 319
Notation......Page 320
References......Page 321
20.1 Introduction......Page 325
20.2 Methods......Page 327
20.3.1 Variations in suspended sediment concentration......Page 328
20.3.2 Time-mean and turbulent flow using clear-water conditions......Page 329
20.3.3 Sediment-laden versus clear-water turbulent flow conditions......Page 330
20.4 Discussion......Page 333
20.5 Conclusions......Page 336
References......Page 337
21.1 Introduction......Page 339
21.1.1 Experimental setup and data collected......Page 341
21.2.1 Physical characteristics of bed topography......Page 342
21.2.2 Multiscale statistics of bed topography......Page 343
21.3.1 Streamwise and vertical velocity spectra: implications for grain sorting......Page 346
21.4 Turbulence patterns modulated by bed forms......Page 349
21.5 Sediment transport modelling......Page 351
21.7 Acknowledgements......Page 352
References......Page 353
22.1 Introduction......Page 357
22.2.1 General methodology......Page 359
22.2.2 Estimating sand elevation......Page 361
22.2.3 Sediment transport......Page 362
22.2.4 Turbulence measurements......Page 363
22.3.1 Turbulence data......Page 365
22.3.2 Sediment transport relation for sand......Page 369
22.4 Conclusions......Page 370
References......Page 371
23.1 Introduction......Page 375
23.3.1 Location and conditions......Page 376
23.3.2 Measurements and sampling mode......Page 377
23.4.2 Frontal structure and turbulence......Page 378
23.4.3 Frontal mixing......Page 379
23.5 Comparison to prior field and laboratory results......Page 383
23.6 Summary......Page 384
References......Page 385
24.1 Introduction......Page 387
24.2.2 Data reduction and analysis......Page 390
24.3 Results and discussion......Page 391
References......Page 397
Index......Page 401