This paper focuses on the sediment particle while it is transported at the limit of deposition in storm sewers, i.e. as bed load at the limit of concentration that leads to sediment deposition. Although many empirical sediment transport equations are known in the literature, there is only limited knowledge concerning particle velocity. Sediment particle and sphere velocity measurements were carried out in two pipe channels and these results led to the development of a semi-theoretical equation for sediment transport at the limit of deposition in sewers. Even in the transport process without deposition, sediment movement is slower than water velocity and depends on the angle of repose of sediment with a diameter d on the roughness k of the pipe channel. Instead of classical dimensionless bed shear stress ψ, a modified dimensionless bed shear stress ψ (d/k)(2/3) was suggested, based on the angle of repose and this parameter was proved to be significant for quantifying the transport capacity. The main purpose of this article is to emphasize the importance of careful observation of experiments. Not only number of tests, but physical understanding are essential for better empirical equations.
This paper presents a comparative study between results obtained in two-dimensional computational simulations performed with three different turbulence models: constant viscosity; Elder Model and k˗Ꜫ Model. The simulations were performed using the software Telemac 2D. These results were compared to data obtained from a study in experimental channel with trapezoidal cross-section and composed of straight stretches and curves. The main objective of this comparison is to explore how turbulence models affect the general behavior of the simulated flow. To support these comparisons, statistical analysis were adopted to quantify the differences between the velocity fields obtained in the simulations and that observed in the experimental channel. The results showed that, despite the theoretical limitations, the use of the simpler turbulence closure model, that is the constant turbulent viscosity, can lead to results as good as or better than those obtained with more sophisticated models.
Flaring Piers and Slit Buckets are structures that can improve the process of energy dissipation and have been implanted in Chinese spillways for at least four decades. These structures basically narrow the passages of the outflow through the spillway, promoting changes in the effluent jets, reducing their erosion potential. However, the literature available on the subject is very limited, and the benefits are disseminated only qualitatively. In order to learn more about how these structures perform, a test program on a hydraulic model was carried out, using a spillway originally designed with a conventional ski jump. The results indicate that there is a correlation between the angle of deflection of the walls that narrow the chute and the depth of the scour hole formed downstream. One of the alternative tests had scour depth 60% smaller than that generated by the spillway without the device, indicating that they can be promising solutions.Keywords: Ski jump; Erosion; Flaring piers; Slit bucket.
RESUMOFlaring Piers e Slit Buckets são estruturas que propiciam melhorar o processo de dissipação de energia e que vem sendo implantadas em vertedouros de barragens chinesas há pelo menos quatro décadas. Trata-se basicamente da implantação de estreitamentos na passagem do escoamento pelo vertedouro que promovem alterações no jato efluente, reduzindo seu potencial erosivo. No entanto, a bibliografia disponível sobre o assunto é bastante restrita e os benefícios são divulgados de forma apenas qualitativa. Visando aprofundar o conhecimento sobre o desempenho dessas estruturas, foi realizado um programa de ensaios em modelo reduzido utilizando um vertedouro projetado originalmente com salto de esqui convencional. Os resultados indicam existir uma correlação entre o ângulo de deflexão dos paramentos que estreitam a calha e a profundidade da fossa de erosão formada a jusante. Uma das alternativas ensaiadas teve profundidade máxima de erosão 60% menor do que aquela gerada pelo vertedouro sem o dispositivo, indicando que podem ser soluções promissoras.
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