Study on drag reduction of a circular cylinder with grooves

Abstract

In the flow around a circular cylinder, a sudden decrease in the drag force occurs at a high Reynolds number, but the same phenomenon occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In previous study of authors, in order to investigate the effect of the depth and number of grooves on a circular cylinder for both arc and triangular grooves, the drag coefficient, pressure, turbulence intensity and velocity distribution were measured. Moreover, the flow around circular cylinders was analyzed by applying the RNG k-ε turbulent model. From these studies, it was found that in order to reduce a drag in a wide range of Reynolds number, the depth and number of grooves is increased and the circular cylinder surface is made to change to a turbulent boundary layer in a low Reynolds number. Furthermore, it was clarified that in order to prevent generating of a separating bubble, capacity of groove is made small and separation is retarded. In this paper, new shape of grooves was developed on the basis of the factor of above-mentioned drag reduction. As a result, the separation point of the circular cylinder with grooves of curved sectional shape shifts to the most downstream side and the drag coefficient becomes the smallest. ©2013 The Japan Society of Mechanical Engineers.