VORTEX - Grupo de Mecânica dos Fluidos de Escoamentos Complexos


Flutuações e Dispersão em Sedimentação com Estratificação na Vertical, (1998)

Autor: Otávio Luiz Silva Rosa

Orientador: Francisco Ricardo Cunha

Resumo
The main subjects studied in this work are the velocity fluctuations and hydro- dynamic dispersion in monodisperse dilute suspensions of rigid spherical particles at low Reynolds number. Each particle is treated as a point of force with excluded volume shell. The sedimentation is held in a rectangular box with periodic sides and impenetrable bot- tom and top. The particles are distributed regularly in the perpendicular to the gravity directions and random and independently in the parallel to the gravity direction. The purpose of this rather unusual inicial microstructure is to try to eliminate the possible ocurrence of secondary convective flows in the horizontal directions that influence the settling velocity variances. The fluctuations in the velocity of individual particles are due to the varying configurations of neighbouring particles and the viscous hydrodynamic interactions between the particles. The variances of the mean velocity of the particles in the initial configurations considered here are depended of the size of the system. Time evolutions of the positions of the particles inside the box are produced during the simu- lations. The long time behavior of the sedimentation process is analysed by the velocity fluctuation self-correlations. The hydrodynamic self-diffusion coeficients are calculated and found to be also depended of the dimensions of the settling reservoir. The diffu- sion process is strongly anisotropic and the impenetrable bottom plays a vital role in the amount of anisotropy. To finish the research, two simulations of sedimentation with blobs are made in order to obtain preliminary results for the problem.

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