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.

Automated summary

This study systematically investigated the hydrodynamic characteristics of a square cylinder near a plane wall boundary under different Reynolds numbers, gap ratios, and turbulent intensities. The findings suggest that the hydrodynamic forces on the cylinder are independent of Reynolds number for small gap ratios, and low turbulent intensity has little effect on the vortex shedding process at larger gap ratios. Additionally, the suppression of vortex shedding was observed with decreasing gap ratios, with the base pressure increasing and drag coefficient decreasing as a result.