ABSTRACT

In this study, a numerical study has been conducted to investigate the behavior of the vortical wake created by a square cylinder placed in a laminar boundary-layer llow. The calculations are performed by solving the unsteady 2D Navier-Stokes equations with a finite-volume method. The Reynolds-number regime investigated is from 500 to 1500. Another parameter that is varied is the location of the cylinder placed from the wall. The initial and subsequent development of the vortex shedding phenomenon are investigated. The presence of the wall is tbund to have strong efl~ects on the properties of these vortices, as well as lift, drag, and Strouhal number.

INTRODUCTION

The problems of vortex shedding from bluff bodies have been extensively studied since the pioneering work of Strouhal (1878) and Von Karman (1912). Excellent surveys of vortex-induced oscillations of bluff bodies havc been given by Bearnaan (1984) and Williamson (1996). Whcn a ~all or ground is present in the flow the shear efl)ct makes the velocity of the approaching stream vary in the direction normal to the bluff body. Then the behavior of vortex shedding behind an obstacle parallel to the ground will be affected significantly. Typical examples are the vibrations of pipe-lines laying on the sea-bottom under the effect of the sea-currents; pipelines and bridges under the effect of the wind, etc. The presence of a wall modifies in a certain number of ways the behavior of the vortical shedding behind a cylinder. When a twodimensional square cylinder is attached to a plane wall, regular vortex shedding is absent (Good and, Ioubert, 1969). When there is a gap between the cylinder and the wall the onset of vortex formation appears at a critical gap height. Fanigushi et al. (1983) found that this value is 0.5 times the side of a square cylinder.

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