Investigations on flow field characteristics of the through-hole cylinders

When the fluids pass a cylinder at certain velocity, the flow separation appears on the cylinder surface, and the separation induced vortexes will also shed from the wall surface to form typical vortex street. These phenomena can lead to the increase of cylinder drag as well as its vibration, and may also collapse the cylinder under certain conditions. In order to decrease the drag and vibration on the cylinders, the large eddy simulation is used to investigate numerically the flow field and force characteristics of both the through-hole circular and square cylinders at Re ? 2.2×105, and obtain their corresponding vortex structures and the drag and lift coefficient curves. After comparing the calculated results of both circular and square cylinders with and without through-holes, the through-hole can not eliminate the vortex shedding, but the vortexes induced by the hole can decrease the size of vortexes shedding from the cylinder, which results in decreasing drag and vibrating amplitude of lift. Therefore, the through-hole of a cylinder can be considered as a simple and practical passive control method of reducing the cylinder drag and vibration.