Flow Patterns Around a Sphere in Terms of Wall Proximity

Flow over a sphere exhibits three-dimensional phenomena even at lower values of Reynolds number (Re). Nonetheless, three-dimensional flow structures may also be affected by boundary layers on the rough walls. For this reason, the effects of wall proximity are very significant for the present case. Regarding these issues, flow characteristics of a sphere have been examined for several gap ratios from G* = 0.01 to G* = 2 at Re = 250. The influence of jet flow between the sphere and the wall has increased by decreasing the gap ratio. Although symmetrical flow patterns have been observed for G* = 1 and G* = 2, this situation is not valid for G* ≤ 0.5 in the present study. It is clearly observed in the wake regions for G* ≤ 0.25 and the positive cross-stream velocity components become more dominant, especially for G* = 0.1 and G* = 0.25, respectively. The positive spanwise vorticity component becomes more dominant; however, the negative one is more dominant for G* ≤ 0.1 in terms of gap ratios. For the case of G* ≤ 0.05, the drag coefficients are less than CD = 0.47 and these values are so close to each other. For G* = 0.1, it is around CD = 0.5 for the present problem. By increasing the gap ratios, drag coefficient values also indicated an increasing trend. Moreover, CD = 0.579 has been attained for the case of G* = 0.25 and it is approximately CD = 0.68 for G* = 0.5 as observed. On the other hand, the values of G* = 1 and G* = 2 approached the values of the uniform flow conditions and the effect of the wall proximity by the boundary layer of the bottom surface disappeared.