Investigation into the physical relationships between water-worked gravel be armours and turbulent in-channel flow patterns
| Project acronym: | HY3-Hull-01 |
| Name of Group Leader: | Dr Katinka Koll, TU Braunschweig, Leichtweiß-Institut für Wasserbau, Braunschweig, katinka.koll@tu-bs.de |
| User-Project Title: | Investigation into the physical relationships between water-worked gravel be armours and turbulent in-channel flow patterns |
| Facility: | Total Environment Simulator |
| Proceedings TA Project: | Investigation into the physical relationship between water-worked gravel bed armours and turbulent in-channel flow patterns |
| Data Management Report: | Data Management Reports Page You will need to login to view this page |
Summary:
Traditional methods for describing turbulent flow account for the effects of a rough sediment boundary using a representative grain size. However, recent studies of gravel bed structure have shown that grain orientation differs for static and dynamic armour layers. Both bed types may be characterised by the same roughness height and surface grain size distribution, but the different arrangement of surface grains results in different longitudinal and transverse roughness scales. The first objective of this study is to investigate how the systematic difference in surface structure affects the spatial and temporal organisation of near bed turbulent flow. The second objective is to compare techniques used to measure velocity and turbulence over rough sediment beds using both Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA). The third objective is to use the data collected to better understand the influence of bed structure on the transfer of fluid momentum both within the roughness elements of the bed and throughout the flow.
The spatially-averaged streamwise velocity profiles and distributions of form induced stresses for the same flow conditions show that grain arrangement has a significant influence on flow roughness. The results indicate that representative surface grain size or bed surface roughness height based on simple statistics of bed elevations cannot accurately account for the resistance imposed by a water-worked gravel bed on the flow. The shape of the vertical profiles as well as the absolute values obtained by PIV measurements depend only marginally on the number of verticals (168 compared to 20). Compared to LDA data, only the longitudinal velocity component shows good agreement. This result is partly associated with the chosen experimental set-up, which aimed at the description of the complete flow field rather than a small section.
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Figure 1. View looking downstream showing one of the sediment trays being lifted before being rotated. |
Figure 2. Experimental instrumentation showing LDA on central gantry support, and PIV light tube on the left with external submersible cameras in black tube to the right. |
| Publication References |
| Observation of the near-bed flow field over gravel bed surfaces with different roughness length scales, in River Flows 2008, Turkey, September 3-5, 2008. Cooper, J.R., Aberle, J., Koll, K., McLelland, S.J., Murphy, B.J., Tait, S.J., Marion, A. 2008. |
| Estimating flow turbulence characteristics over water-worked gravel beds using LDA and PIV measurement systems, in River Flows 2008, Turkey, September 3-5, 2008. Koll, K., Tait, S.J., Cooper, J.R., Aberle, J., McLelland, S.J., Murphy, B.J., Massaro, G. 2008. |