Flow past a square cylinder with an angle of incidence Phys. Fluids 22, 043603 (2010); 10.1063/1.3388857Characteristics of two-dimensional flow around a rotating circular cylinder near a plane wallThe steady motion of a viscous fluid in a cylindrical container with a partially rotating bottom wall and a free surface is investigated by means of axisymmetric Navier-Stokes simulations. The flow above the spinning disk at the center of the bottom wall is dominated by an Ekman boundary layer that drives the fluid radially outward. In contrast, an inward flow ensues along the outer, stationary part of the bottom wall, where the radially increasing pressure distribution set up by the rotating fluid motion near the free surface is not balanced by a corresponding centrifugal force. As a result, flow separation occurs at an intermediate radial location close to the outer edge of the rotating disk. Thus a flow configuration results that is dominated by a meridional vortex above the spinning disk, and a counterrotating vortex above the stationary part of the bottom wall. Simulations are conducted for various aspect ratios and Reynolds numbers, in order to evaluate the resulting changes in the vortex breakdown configurations. As the ratio of container radius to disk radius increases above a value of about 2.3, the influence of the lateral container wall on the features of the central flow in the neighborhood of the spinning disk becomes insignificant. By means of a simplified model problem, it is demonstrated that this rapid loss of influence is due to the exponential decay of the azimuthal surface velocity beyond the edge of the disk. This exponential decay is confirmed by the numerical data, and it reflects the fact that as the lateral wall moves outward, the stationary part of the end wall becomes the main sink for the azimuthal momentum of the fluid.

In continuous casting, the molten steel is poured from the ladle to the tundish through a nozzle located at the bottom of the ladle. This process, however, must be stopped before the ladle is completely emptied to avoid slag carryover to the tundish. The amount of steel that remains unteemed in the ladle is usually significant, so steel plants are highly interested in studying different ways to improve the process. In the present work, experimental studies using water models and numerical simulations have been employed to analyse the conditions needed for vortex formation and investigate the influence of geometrical and flow parameters on the amount of wasted steel. Both experimental and numerical results lead to the conclusion that no vortex formation is expected to take place during ladle drainage under industrial conditions.

In this paper, the onset of motion of an isolated cylinder partially exposed to a shear flow is experimentally investigated. The experiments are performed in a small narrow channel which provides a vertical shear layer flow whose sizes correspond with the channel width. The bottom of the channel is smooth except in the test zone, at long distance from the inlet, where the cylinder is placed with its principal axis perpendicularly directed to the main flow. The geometry of the channel bottom at the test zone is such that the cylinder is partially buried and presents different expositions to the incident flow. In this way, the geometrical constraints imposed by the sediment bed on a single particle in a natural sediment transport situation are reproduced in an idealized context. The results are interpreted in terms of the relation between the particle mobility parameter at the critical condition and the here defined particle burial degree with respect to the bed geometrical constraints beta . We emphasize the role played by this burial degree that is dependent on the particle exposure to the incident flow E and the resistance to the motion by mechanical contacts with its surroundings given by the so-called static pivot angle varphi .

This contribution presents particle image velocimetry measurements for an open channel stationary uniform and fully developed flow of water over a horizontal flat bed of uniform glass beads in presence of a staggered array of vertical cylindrical stems. The main objective was to explore and quantify the influence of the stems-to-flow relative submergence, h v / h, over the mean flow and local turbulence intensities. A comparison with measurements for the non-vegetated flow over the same granular bed is presented. Results indicate a remarkable influence of h v / h over the whole flow field. The time-average mean flow presents a strong spatial variation in the layer of the flow occupied by the stems. The local velocity fluctuations are strongly affected by the presence of the stems, with regions in between the stems where they reach peaks that are several times larger than those encountered in the flow in absence of vegetation. The turbulence intensity profiles are noticeably different when compared to those measured in the non-vegetated flow conditions. From previous works it was possible to derive an equation for the mean velocity, U v , of the flow through the vegetated layer of height h v . The prediction of this equation is in good agreement with the uniform value for the double-average longitudinal velocity profile in this layer. A final brief discussion about the possible impact of these vegetated-flow features on the sediment transport is presented.

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