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ISSN 在线: **2379-1748**

ISBN 打印: **978-1-56700-517-2 (Flash drive)**

5-6th Thermal and Fluids Engineering Conference (TFEC)

The flow around a cylinder rolling along a horizontal ground plane is investigated using direct numerical simulation for a Reynolds numbers based on the cylinder diameter, *D*, of Re_{D} = 3 × 10^{4}. Three cylinder thicknesses, *T/D* = 0.040, 0.126, and 0.400, are considered, with the aspect ratio of the thinnest cylinder
approximating that of a bicycle tire, and the thickest representative of an automotive vehicle tire. The timeaveraged
drag coefficients are found to be 0.87, 0.69, and 0.97 for the three cylinders, respectively. The nonmonotonic variation in drag coefficient with thickness suggests a transition in the proportion of contributions from friction and pressure drag to the total drag. Indeed, the ratio of friction drag to pressure drag varies from 0.333 to 0.085 to 0.013 for the three cylinders. Temporal fluctuations in the drag coefficient associated with vortex shedding events increase monotonically with thickness, though the root-mean-square of the drag
coefficient follows the same trend as the mean drag coefficient. The lift coefficients are −0.057, 0.066, and
0.64 for the three respective cylinders. The negative value for the thinnest cylinder indicates down force. The transition from negative lift on the thin wheel to positive lift on the thick wheel is associated with elevated surface pressure just upstream of the ground contact point as thickness increases.

**Video presentation**