Steady flow around a square cylinder near a plane boundary

Steady flow around a square cylinder placed near a plane wall boundary is investigated experimentally in the present work covering the range of Reynolds number of Re = 7.34 x 10(4)-4.12 x 10(5), gap ratios of G/D = 0-3 with two different freestream turbulent intensity I-u = 1% and 9%. The influence of Reynolds number, gap ratios and turbulent intensity on the hydrodynamic characteristics have been studied systematically. Two-dimensional Large-eddy simulation (LES) were employed for flow visualizations. It is found that the hydrodynamic forces on a square cylinder are independent of Re even for the very small gap ratio cases. For the influence of the low turbulent intensity (I-u = 1%), the hydrodynamic features and vortex shedding are insensitive to the gap effect as G/D > 1. With the decrease of G/D, the increase of the base pressure C-pb results in the decrease of the drag coefficient CD. The amplitude of the periodic fluctuations of the vortex shedding process decreases with the vortex shedding process continuing. As G/D < 0.3, the vortex shedding is observed to be completely suppressed. The blockage effect leads to an entrainment of the flow passing through the gap and a low-speed recirculation is formed at the plane boundary in the region of x/D < 7.75. High turbulence tends to increase the base pressure and reduce the drag coefficient of the square cylinder for large gap ratio. For G/D <= 0.8, the high turbulence triggers the growth of separated shear layer and inherent instabilities for the near-wall cylinder, which results in the higher fluctuating drag and lift coefficient. The critical gap ratio for the vortex shedding suppression is reduced to G/D = 0.2.