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Bed-Load effects on hydrodynamics of rough-bed open-channel flows

Bed-Load effects on hydrodynamics of rough-bed open-channel flows
Bed-Load effects on hydrodynamics of rough-bed open-channel flows
The extent to which turbulent structure is affected by bed-load transport is investigated experimentally using a nonporous fixed planar bed comprising mixed-sized granular sediment with a d50 of 1.95?mm. Three different sizes of sediment (d50 = 0.77, 1.99, and 3.96?mm) were fed into the flow at two different rates (0.003 and 0.006?kg/m/s), and subsequently transported as bed load. Particle image velocimetry (PIV) was used to determine the turbulence characteristics over the fixed bed during clear water and sediment feed cases. Mean longitudinal flow velocities at any given depth were lower than their clear water counterparts for all but one of the mobile sediment cases. The exception was with the transport of fine grains at the higher feed rate. In this case, longitudinal mean flow velocities increased compared to the clear water condition. The coarse grains tended to augment bed roughness, but fine grains saturated the troughs and interstices in the bed topography, effectively causing the influence of bed irregularities to be smoothed. The PIV technique permitted examination of both temporal and spatial fluctuations in flow variables: therefore many results are presented in terms of double-averaged quantities (in temporal and spatial domains). In particular, the form-induced stress, which arises from spatially averaging the Reynolds averaged Navier–Stokes equations and is analogous to the Reynolds turbulent stress, contributed between 15 and 35% of the total measured shear stress in the roughness layer. Flow around protrusive roughness elements produced a significant proportion of the turbulent kinetic energy shear production, suggesting that this process is highly intermittent near rough beds
576-585
Campbell, L.
55f0f877-c982-4898-b9c0-b03474d3656c
McEwan, I.
c768d60c-6fe7-4b35-89a2-105cbf0a19b5
Nikora, V.
eb1445fd-f8be-429c-af56-2d24d0b9ff7d
Pokrajac, D.
bf6480dd-6965-46f1-880b-8290c86f6965
Gallagher, M.
6d35475a-560d-4926-8f22-fbd5ad558146
Manes, C.
7d9d5123-4d1b-4760-beff-d82fe0bd0acf
Campbell, L.
55f0f877-c982-4898-b9c0-b03474d3656c
McEwan, I.
c768d60c-6fe7-4b35-89a2-105cbf0a19b5
Nikora, V.
eb1445fd-f8be-429c-af56-2d24d0b9ff7d
Pokrajac, D.
bf6480dd-6965-46f1-880b-8290c86f6965
Gallagher, M.
6d35475a-560d-4926-8f22-fbd5ad558146
Manes, C.
7d9d5123-4d1b-4760-beff-d82fe0bd0acf

Campbell, L., McEwan, I., Nikora, V., Pokrajac, D., Gallagher, M. and Manes, C. (2005) Bed-Load effects on hydrodynamics of rough-bed open-channel flows. Journal of Hydraulic Engineering, 131 (7), 576-585. (doi:10.1061/(ASCE)0733-9429(2005)131:7(576)).

Record type: Article

Abstract

The extent to which turbulent structure is affected by bed-load transport is investigated experimentally using a nonporous fixed planar bed comprising mixed-sized granular sediment with a d50 of 1.95?mm. Three different sizes of sediment (d50 = 0.77, 1.99, and 3.96?mm) were fed into the flow at two different rates (0.003 and 0.006?kg/m/s), and subsequently transported as bed load. Particle image velocimetry (PIV) was used to determine the turbulence characteristics over the fixed bed during clear water and sediment feed cases. Mean longitudinal flow velocities at any given depth were lower than their clear water counterparts for all but one of the mobile sediment cases. The exception was with the transport of fine grains at the higher feed rate. In this case, longitudinal mean flow velocities increased compared to the clear water condition. The coarse grains tended to augment bed roughness, but fine grains saturated the troughs and interstices in the bed topography, effectively causing the influence of bed irregularities to be smoothed. The PIV technique permitted examination of both temporal and spatial fluctuations in flow variables: therefore many results are presented in terms of double-averaged quantities (in temporal and spatial domains). In particular, the form-induced stress, which arises from spatially averaging the Reynolds averaged Navier–Stokes equations and is analogous to the Reynolds turbulent stress, contributed between 15 and 35% of the total measured shear stress in the roughness layer. Flow around protrusive roughness elements produced a significant proportion of the turbulent kinetic energy shear production, suggesting that this process is highly intermittent near rough beds

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Published date: July 2005
Organisations: Energy & Climate Change Group

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Local EPrints ID: 204087
URI: https://eprints.soton.ac.uk/id/eprint/204087
PURE UUID: 340dff33-47c2-414f-8b55-e55d2d850769

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Date deposited: 24 Nov 2011 10:06
Last modified: 18 Jul 2017 11:07

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