Date of Award

2009

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

Keywords

Water Resources Engineering.

Supervisor

Balachandar, Ramaswami (Civil and Environmental Engineering)

Rights

info:eu-repo/semantics/openAccess

Abstract

A comprehensive study was carried out to understand the effects of roughness, seepage and ice cover on the turbulence characteristics of flow in an open channel. To this end, tests were conducted with four different types of bed surface conditions. This includes the use of an impermeable smooth bed, impermeable rough bed, permeable sand bed and an impermeable bed with distributed roughness. Both suction and injection seepage tests were conducted covering a range of seepage rates. For the ice cover tests, two different cover conditions were used. The tests were conducted at two different Reynolds number (Re = 47,500 and 31,000). The bed roughness effect on the turbulence characteristics is seen to have penetrated through most of the flow depth, disputing the wall similarity hypothesis initially proposed by Townsend (1976). The results show that the distributed roughness shows the greatest roughness effect. Although the same sand grain is used to create the different rough bed conditions, there are differences in turbulence characteristics, which is an indication that specific geometry of the roughness has an influence. Roughness increases the contribution of the extreme turbulent events which produces very large instantaneous Reynolds shear stress and can potentially influence the sediment transport, resuspension of pollutant from the bed and alter the nutrient composition, which eventually affects the sustainability of benthic organisms. For the tests with seepage, injection increases the magnitude of the various turbulent characteristics and suction reduces the values in comparison to no-seepage condition. Effect of seepage on different turbulent characteristics is not restricted to the near-bed region but can be seen through out the flow depth. The results from the analysis of turbulent bursting events clearly show a distinct effect of seepage well beyond the near-bed region. The introduction of ice cover causes a change in mean velocity profile and increases total resistance of the channel. The magnitude of this change depends on both the bed and the cover roughness. The change in turbulent characteristics seems to be bound to the upper half of the flow and the changes can be significant with the rougher cover.

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