Skip to main content
Article thumbnail
Location of Repository

Coherent flow structures in a depth-limited flow over a gravel surface : the role of near-bed turbulance and influence of Reynolds number.

By R. J. Hardy, J. L. Best, S. N. Lane and P. E. Carbonneau

Abstract

In gravel bed rivers, the microtopography of the bed exerts a significant effect on the generation of turbulent flow structures. Although field and laboratory measurements have indicated that flows over gravel beds contain coherent macroturbulent flow structures, the origin of these phenomena, and their relationship to the ensemble of individual roughness elements forming the bed, is not quantitatively well understood. Here we report upon a flume experiment in which flow over a gravel surface is quantified through the application of digital particle imaging velocimetry, which allows study of the downstream and vertical components of velocity over the entire flow field. The results indicate that as the Reynolds number increases (1) the visual distinctiveness of the coherent flow structures becomes more defined, (2) the upstream slope of the structures increases, and (3) the turbulence intensity of the structures increases. Analysis of the mean velocity components, the turbulence intensity, and the flow structure using quadrant analysis demonstrates that these large-scale turbulent structures originate from flow interactions with the bed topography. Detection of the dominant temporal length scales through wavelet analysis enables calculation of mean separation zone lengths associated with the gravel roughness through standard scaling laws. The calculated separation zone lengths demonstrate that wake flapping is a dominant mechanism in the production of large-scale coherent flow structures in gravel bed rivers. Thus, we show that coherent flow structures over gravels owe their origin to bed-generated turbulence and that large-scale outer layer structures are the result of flow-topography interactions in the near-bed region associated with wake flapping

Topics: Gravel bed rivers, Coherent flow structures, Wavelet analysis.
Publisher: American Geophysical Union
Year: 2009
DOI identifier: 10.1029/2007JF000970
OAI identifier: oai:dro.dur.ac.uk.OAI2:7334
Journal:

Suggested articles

Citations

  1. (2005). 1 min in the life of a river: Selecting the optimal record length for the measurement of turbulence in fluvial boundary layers,Geomorphology,68, 77–94,
  2. (2000). A field study of turbulence and sediment dynamics over subaqueous dunes with flow separation,
  3. (1972). A First Course in Turbulence,
  4. (1998). A practical guide to wavelet analysis,
  5. (1973). A visual study of turbulent shear flow,
  6. (1999). Application of an acoustic particle flux profiler in particle-laden open-channel flow,
  7. (1999). Are weakly mobile-bed flows a special class of wall-bounded flows?,
  8. (1998). Assessment of DEM quality for characterizing surface roughness using close range digital photogrammetry,
  9. (1992). Burst-like sediment suspension events in a sand bed river,
  10. (1992). Changes in velocity profiles at roughness transitions in coarse grained channels,
  11. (1996). Coherent flow structures in smooth-wall turbulent boundary layers: Facts, mechanisms and speculation, in Coherent Flow Structures in Open Channels,
  12. (2003). Cost-effective non-metric close-range digital photogrammetry and its application to a study of coarse gravel river beds,
  13. (2005). Development and testing of a numerical code for treatment of complex river channel topography in three-dimensional CFD models with structured grids,
  14. (1991). Digital particle image velocimetry,
  15. (1949). Dynamics of Alluvial Flows
  16. (2007). Emergence of coherent flow structures over a gravel surface: A numerical experiment,
  17. (1992). Estimation of flow resistance in gravel-bedded rivers: A physical explanation of the multiplier of roughness length,
  18. (1992). Evolution of coarse gravel bed forms: Field measurements at flood stage,
  19. (1985). Experimental study of secondary currents in open channel flow, paper presented at 21st IAHR Congress,
  20. (2001). Field investigation of three dimensional flow structure at stream confluences,
  21. (2000). FlowMap: Particle image velocimetry instrumentation,
  22. (1997). Fundamental of digital particle image velocimetry,
  23. (1990). Fundamentals of the Dynamics of Alluvial Flows (in Russian),
  24. (1996). Generalized scaling of coherent bursting structures in the near-wall region of turbulent flow over smooth and rough boundaries, in Coherent Flow Structures in Open Channels,
  25. (1966). Investigation of the flow turbulent structure (in
  26. (2004). Junction flow systems: Mechanics and implications for natural flows,
  27. (1978). Kinematic studies of the flow around free or surface mounted obstacles: Applying topology to flow visualization,
  28. (1973). Laboratory investigations of the kinematic structure of turbulent flow over a rough bed (in Russian), Trans. State Hydrol.
  29. (1984). Large-scale structure of turbulent flow in a rectangular flume (in Russian), Trans. State Hydrol.
  30. (2001). Macroturbulent structure of openchannel flow over gravely beds,
  31. (1973). Measurements of structure of Reynolds stress in a turbulent boundary layer, doi
  32. (1989). Mechanics of flow over ripples and dunes, doi
  33. (1993). Monitoring and analysis of turbulence in geophysical boundaries: Some analytical and conceptual issues, in Turbulence: Perspectives on Flow and Sediment Transport, edited by
  34. (1981). New aspects of turbulent boundary layer structure,
  35. (2004). Numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment,
  36. (1997). On errors of digital particle image velocimetry,
  37. (1991). On the dynamics of near-wall turbulence,
  38. (1986). On the vortex formation in the mixing layer behind dunes,
  39. (1953). Principal results of experimental study of the structure of turbulent flows, inProblem of Channel Processes
  40. (2000). Rainfall-runoff relations for karstic springs. Part II: Continuous wavelet and discrete orthogonal multiresolution analyses,
  41. (1988). River Turbulence (in Russian),
  42. (1995). Role of near-bed turbulence structure in bed load transport and bed form mechanics, doi
  43. (2001). Scales of boundary resistance in coarse-grained channels: Turbulent velocity profiles and implications,
  44. (1996). Scales of turbulent coherent flow structures in a gravel bed river,
  45. (1999). Sediment-laden flow in open-channels under noncapacity and capacity conditions,
  46. (1986). Simultaneous flow visualization and Reynolds stress measurement in a turbulent boundary layer,
  47. (2004). Size, shape and dynamics of large-scale turbulent flow structures in a gravel-bed river,
  48. (2007). Spatial scale partitioning of in situ turbulent flow data over a pebble cluster in a gravel-bed river,
  49. (2001). Statistical evidence of hairpin vortex packets in wall turbulence,
  50. (1971). Structural features of turbulent flow over smooth and rough boundaries,
  51. (1989). Suspended sediment concentration in relation to surface-flow structure in Squamish River estuary,
  52. (1971). The production of turbulence near a smooth wall in a turbulent boundary layer,
  53. (1986). The three dimensional structure of turbulent shear flow in an open channel, paper presented at
  54. (1990). The variability of critical shear stress, friction angle, and grain protrusion in water-worked sediments,
  55. (1990). The wavelet transform: Some applications to fluid dynamics and turbulence,
  56. (2002). Throughwater close-range digital photogrammetry in flume and field environments,
  57. (1997). Turbulence characteristics of New Zealand gravel-bed rivers, doi
  58. (1993). Turbulence driven secondary flows and the formation of sand ridges,
  59. (1991). Turbulence in Water Flows
  60. (1974). Turbulence of Open-Channel Flows
  61. (1982). Turbulence structure and transport mechanism at the free surface in an open channel flow,
  62. (1988). Turbulence structure in free-surface channel flow,
  63. (1989). Turbulent boundary layer separation,
  64. (1979). Turbulent flow in a depth limited boundary layer, doi
  65. (1991). Velocity distribution and bed roughness in high-gradient streams,
  66. (1982). Visualisation of the mixing layer behind dunes, in Mechanics of Sediment Transport,
  67. (1986). Visualization of longitudinal eddies in an open channel flow, in Flow Visualization IV:
  68. (1991). Vortical structures and coherent motion in turbulent flow over smooth and rough boundaries,
  69. (1991). Vortices in hydraulics,
  70. (1992). Wavelet transforms and their application to turbulence,

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.