Unsteady Characteristics of Flow around a Circular Cylinder with Grooves

概要

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The flow around a cylinder in uniform flow in many kinds of behavior due to the effects of Reynolds number. In particular, the sudden decrease in the drag force at a certain Reynolds number is well known. Although this phenomenon occurs nearby Re=3×10^5,the same phenomenon occurs at a lower Reynolds number in the case that there exist grooves or roughnoss on the cylinder surface. This phenomena is applied to the dimples on a golf ball and the grooves on the low wind pressure cable and the pipe jumper covering the cable and is very important from the point of view of engineering, too. The flying distance of a golf ball is increased by the dimples, and the drag force acting on the cable can be decreased by virtue of the grooves on the low wind pressure cable and the pipe jumper. In this report, in order to make clear the unsteady flow characteristics around a cylinder with grooves, the unsteady flow analysis was performed applying the turbulent model to a flow around a cylinder with grooves each of whose section shapes being as same as that of a dimple on a golf ball, with changing Reynolds number. This result made clear the unsteady characteristics of lift and drag, Strouhal number, flow pattern behind the cylinder, pressure distribution and separation points. Moreover, the time averages of these values almost agreed with the experimental valucs.
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