Drag and Flow Characteristics around the Circular Cylinder with Grooves.

It is well-known the dimples on the surface of a golf ball increase in flying distance and the drag force of the pipe jumper that used as the conductor of the high-voltage transmission is decreased by the grooves on the surface of the pipe jumper. But it has not been clarified completely how dimples and grooves manipulate the flow. The final goal of our research is to make clear the drag reduction mechanism of grooves and dimples and the detailes of the related flow structures. As the first stage of this research, this paper deals with the influence of the depth of grooves on the cross-flow around a circular cylinder. Pressure distribution and drag and lift coefficients were measured in a uniform flow in the Reynolds number range of 8.6×103≤Re≤5×105. The Reynolds number regime was classified by the variation in the drag coefficient with Reynolds number. Pressure distributions and drag and lift coefficients showed the characteristic changes for subcritical, critical, and supercritical Reynolds number ranges, respectively. As the depth of grooves decreased, drag coefficient became lower, and the critical points shifted into the high Reynolds number range. Lift was generated in the range of critical Reynolds number, even though a circular cylinder was not rotating.