The evolution of the cellular structure of the two-dimensional creeping flow induced by a rotating circular cylinder set in the centre of a rectangular channel is studied numerically and experimentally when the aspect ratio A increases from 1 to 7. In the calculations, depending on the value of A, either only series in terms of polar coordinates, or both matched polar and Cartesian coordinates series are employed to represent the stream function and an efficient least-squares method, very easy to program, is selected to satisfy some of the boundary conditions. For the experiments, a special technique which visualizes intermittently the paths of solid tracers during long times of exposure permits us to observe the fluid motion in the whole domain, even in the regions where the velocities are very small. An excellent measure of agreement between the numerical and experimental results is found. Thus it is clearly shown how, in the region beyond the rotating flow directly driven by the cylinder, the two main corner cells visualized at A = 1, develop with increasing A and then coalesce, to finally merge and give rise to a single central cell. This central cell develops in its turn, tending finally to the unbounded channel reference cell, after passing through a maximum length however. Owing to the very high precision of the calculations, many details of the flow development have been clearly shown, in particular the periodicity, with increasing A, of all the different phases, progressively inducing a succession of cells. The prediction that the angle of separation of the fluid boundaries of the cells tends towards the theoretical limit of 58.61° when the aspect ratio becomes large is also confirmed.

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Complex matter may take various forms from granular matter, soft matter, fluid-fluid, or solid-fluid mixtures to compact heterogeneous material. Cellular automata models make a suitable and powerful tool for catching the influence of the microscopic scale in the macroscopic behavior of these complex systems. Rather than a survey, this paper attempts to bring out the main concepts underlying these models. A taxonomy is presented with four general types proposed: sandpile, latticegas, lattice-grain, and hybrid models. A discussion follows with general questions; namely, grain-size, synchronization, topology and scalability, and consistency of the models.

In this work, Discrete Element Method (DEM) is used in order to calculate the motion of granular material in rotating dryers. We are particularly interested in analysing the effect of flight shape on the behaviour of spherical particles in the cross section of the dryer. We will be using two segments flights and three different profiles : a straight flight (180 • between both segments), an angled flight (with an angle of 120 •) and a rightangled flight (90 •). The results show that the profile of the flight affects significantly the motion of the particles in the cross section of the dryer. Changing the angle between the segment's flight, changes the flight loading and thus the material holdup which leads to different discharging profiles of the flight. For a right angled flight, the range of the discharge angle increases leading to a more uniformized cascade pattern in time and an enlarging of the area occupied by the curtains of particles. The specific durations (discharging time, falling time) are also determined and studied as a function of the flight shape.