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No description available.

The spatial variability in turbulent flows over water-worked gravel beds has been studied. Spatially distributed measurements of velocity were obtained using Particle Image Velocimetry for a range of hydraulic conditions over two water-worked gravel beds. A different approach to bed formation was achieved by feeding sediment into a flume to form deposits that result from the, arrangement of the grains by the flow, as would be observed in a river. It was shown that, even over macroscopically flat deposits, time-averaged streamwise velocities display considerable spatial variability. However, the level of variability was a magnitude lower for time-averaged vertical velocities. The degree of spatial variability in both streamwise and vertical velocities was shown to increase with relative submergence. Spatial flow variability was present in the logarithmic and outer regions of the flow, which contradicts previous thinking that spatial variability is only present in the near bed form-induced sublayer. The time-averaged flow velocities displayed a considerable degree of organisation over both beds, indicating the existence of spatially coherent time-averaged flow structures. Form-induced stresses caused by the spatial heterogeneity in the flow were estimated. These were found to be significant for flows over both beds, and did not disappear above the form-induced sub layer as previously thought. Measurements of Reynolds stress alone, whether spatially-averaged or not, cannot be used to determine the mean bed shear stress over water-worked gravel beds. Increases in relative submergence resulted in changes in the level of momentum carried by spatial deviations in the flow, and by inference, those carried by the turbulent fluctuations. This occurred even when the average rate of momentum transfer at the bed was the same. It was concluded that relative submergence could have a more important influence on the spatial variability of fluid stresses than the bed surface topography of water-worked gravel deposits.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

An experimental and theoretical investigation is reported on the asymmetric, quasi-parallel flow of turbulent incompressible fluids. The experimental programme consisted of providing detailed measurements of mean and turbulent characteristics of the fully developed flow in a plane channel having one smooth wall, while the other was roughened by transverse square ribs. The dissimilar wall conditions imposed a strong asymmetry upon both mean and turbulent flow fields bringing into prominance several interating features that are concealed in the symmetric flow situations. The theoretical investigation concerned the provision of a procedure capably of accurate prediction of strongly asymmetric quasi-parallel flows. The research was concentrated upon the physical aspect of the problem, that is the establishment and testing of an approximate closed set of the transport equations, sufficient for the accurate description of the considered flows. Two physical models have been explored, both of which used the Spalding-Patankar numerical method for the solution of resulting equations. The first model, based upon the extension of Kolmogaa Prandtl eddy viscosity formula was tested in plane all-smooth and smooth-rough channels. It showed several deficiencies and was subsequently discarded. A second model was established that is described by a closed set of four partial differential equations for conservation of mean momentum, turbulent shear stress, turbulent kinetic energy and its clissipation. This model was extensively tested is several types of duct flows, wall boundary layers and quasi-parallel free flows. With a single set of empirical constants, the model yielded predictions of various flow properties which were in good agreement with experiments.