Control of circular cylinder flow by the use of dimples

Measurements are reported of the drag coefficient and Strouhal number of a dimpled circular cylinder over the Reynolds number range from 2 x 104 to 3 x 10s. The ratio of the depth of the dimples to the diameter of the cylinder is 9xlO~ 3. In common with sand-roughened cylinders, the dimpled cylinder has a lower critical Reynolds number than a smooth cylinder. After the drag coefficient minimum, the CD does not rise to the high values that are typical of cylinders with sand roughness but is found to be closer to that for a smooth cylinder. Over a Reynolds number range from about 4xl04 to 3xl05, a dimpled circular cylinder has a lower drag coefficient than a smooth cylinder.