| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 106 === Though Magnus effect and its application had been widely investigated by many scientist and researchers, its behavior under the influence of the near ground effect has recently acquired much attention. However, most studies considered the ground effect as a static surface without relative velocity towards the subject. Therefore, this research is aimed to numerically and experimentally investigate the flow interaction around a rolling cylinder that shifts towards a flat surface in a uniform flow. Further, the results in the dy- namic case were compared to the static cases under both 2 dimensional and 3 dimensional aspects.
Some important normalized parameters of the rolling cylinder being discussed through- out the entire investigation are the rotation ratio α, declining velocity ratio β, and the spac- ing gap between the cylinder and the flat surface SG. The range of interest for α is from 0 to ±0.2, and SG from 5D to 0.5D, where D is the diameter of the rolling cylinder chosen to be 2 cm and 3 cm. Note that three types of classification are distinguished according to the rotation motion of the cylinder: One is when the cylinder has non-rotation (α = 0); another would be the cylinder rotating in counterclockwise direction (α > 0); and the other is the clockwise rotation (α < 0) of the cylinder.
The results show that the flow pattern significantly varies in each of the three distin- guished types of rotation motion. In the first case, when the cylinder is non-rotation, the ground effect mitigates eddies behind the subject and leads to a higher lift and drag. In the second case, when the cylinder is counterclockwise-rotation, as SG is decreasing, the lift and drag drops, and the separation frequency increases. The vortex around the cylinder is alleviated by the ground effect, and the separation occurs at a lower portion behind the cylinder due to the effect of the incoming flow and declining motion. In the last case, when the cylinder is clockwise-rotation, As SG decreases, the lift and the separation frequency decreases, and the drag increases. The vortex is strengthened by the ground effect, and the separation occurs at a higher portion with the same reasoning. Further, the stability analysis is applied to the three distinguished motions to check for their stability.
As a result, the phenomenon of the flow patterns are consistent in both static and dynamics cases, but the force exerted on the cylinder is smaller for the dynamic case.
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