Direct numerical simulation of different finite cylinders rolling on a horizontal surface: The thickness effects on the aerodynamics

Abstract

The flow around a cylinder rolling along a horizontal ground plane is investigated using direct numerical simulation for a Reynolds number based on the cylinder diameter, D, of ReD=3×104. Three cylinder thicknesses, T/D=0.040, 0.126, and 0.400, are considered. The time-averaged drag coefficients are found to be 0.87, 0.69, and 0.97 for the three cylinders, respectively. The non-monotonic variation in drag coefficient with thickness suggests a transition in the proportion of contributions of friction and pressure drag to the total drag which changes about 30% with thickness increase. Indeed, the ratio of friction drag to pressure drag varies from 0.333 to 0.085 and finally to 0.013 for the three cylinders. The pressure coefficient become more negative in the aft of the thicker cylinders, because the cylinder become more bluff body which suggests more pronounced pressure drag. 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 cylinder to positive lift on the thick cylinder is associated with elevated surface pressure just upstream of the ground contact point as thickness increases. As the flow is more detached from the cylinder sides, the friction lift is less significant with thickness increase. Furthermore, the pressure coefficient is negative spatially larger in the top of the thicker cylinders which the expansion offers a more significant upward pressure lift.