A volume-filtered Large-Eddy Simulation (LES) of oscillatory flow over a rippled mobile bed is conducted using an Euler-Lagrange approach. As in unsteady marine flows over sedimentary beds, the experimental data, referenced in this work for validation, shows quasi-steady state ripples in the sand bed under oscillatory flow. This work approximately reproduces this configuration with a sinusoidal pressure gradient driven flow and a sinusoidally rippled bed of particles. The LES equations, which are volume-filtered to account for the effect of the particles, are solved on an Eulerian grid, and the particles are tracked in a Lagrangian framework. In the Discrete Particle Method (DPM) used in this work, the particle collisions are handled by a soft-sphere model, and the liquid and solid phases are coupled through volume fraction and momentum exchange terms. Comparison of the numerical results to the experimental data show that the LES-DPM is capable of capturing the mesoscale features of the flow. The large scale shedding of vortices from the ripple peaks are observed in both datasets, which is reflected in the good quantitative agreement between the wall-normal flow statistics, and good qualitative agreement in ripple shape evolution. Additionally, the numerical data provides three insights into the complex interaction between the three-dimensional flow dynamics and bed morphology: (1) there is no observable distinction between reptating and saltating particle velocities, angular velocities or observed Shields parameters; (2) the potential motion of the mobile bed may create issues in the estimation of the bed shear stress used in classical models; and, (3) a helical pairing of vortices is observed, heretofore not known to have to have been identified in this type of flow configuration.

Made available in DSpace on 2014-12-17T15:01:17Z (GMT). No. of bitstreams: 1 NorbertoAM.pdf: 1190502 bytes, checksum: 15fc3890db7720ac4fcdf9c75747130a (MD5) Previous issue date: 2005-12-15 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / This work aims to use a different hydrodynamic condition applied to a new design of mixer-settler on treating wastewater produced by petroleum industry, called MDIF (Misturador-Decantador ? Invers?o de Fases/ Mixer-Settler based on Phase Inversion MSPI). The use of this different hydrodynamic behaviour is possible due to vertical disposition of the device and the principle of Phase Inversion that controls the MDIF, providing the generation (creation) of a cascade of drops, into an organic layer, that works as micro-decanters, thus making possible the formation of a bed of non-coalesced drops, called Bed Formation . The use of this new hydrodynamics condition allows to increase the residence time of the oil carrier drops, into an organic layer, and the device can treat a greater volume of wastewater. In view of to get this condition it is necessary to operate at high throughput (58,6 m3.m-2.h-1). By results, the condition of Bed Formation is the best one to be used when MSPI operates with throughput up to 58,6 m3.m-2.h-1. The results using the condition of Bed Formation show that increasing the height of the bed of non-coalesced drops and/or decreasing the volumetric ratio (O/A) an increase of the separation efficiency is detected / Este trabalho objetiva utilizar uma diferente condi??o hidrodin?mica aplicada a um novo design de misturador-decantador aplicado ao tratamento de ?guas produzidas da ind?stria do petr?leo, que vem sendo denominado de MDIF (Misturador-Decantador ? Invers?o de Fases). A utiliza??o do regime hidrodin?mico de Leito Denso ? poss?vel devido a disposi??o vertical do aparelho e ao princ?pio de invers?o de fases que rege o MDIF, proporcionando a gera??o de uma cascata de gotas, na regi?o de leito org?nico, que funcionam como micro-decantadores, possibilitando assim a forma??o de um leito de gotas n?o-coalescidas, denominado de Leito Denso. A utiliza??o desta nova condi??o hidrodin?mica permite o aumento do tempo de resid?ncia da gota transportadora de ?leo, na regi?o de leito org?nico, e o trata um maior volume de ?gua produzida, visto que para se atingir esta condi??o ? necess?rio se operar a altas vaz?es (58,6 m3/m2h). A partir dos resultados obtidos, a condi??o de regime de leito denso mostra-se como a melhor condi??o a ser utilizada quando se opera o misturador-decantador ? invers?o de fases com vaz?es espec?ficas acima de 58,6 m3.m-2.h-1. Os resultados utilizando o regime de leito denso mostram que elevando-se a altura do leito de gotas n?o-coalescidas e/ou diminuindo a raz?o volum?trica org?nico/aquoso aumenta a efici?ncia de separa??o do aparelho