On the critical Reynolds number of the drag coefficient for a circular cylinder

Drag coefficient of a circular cylinder in a uniform flow shows a steep fall when the Reynolds number increases from about 3.0 x 10(exp 5) to about 3.8 x 10(exp 5) in our experiments. At about Re = 3.6 x 10(exp 5), the drag coefficient curve is not continuous, but has a jump, and also a lift force actually acts on the cylinder. This phenomenon results from the sudden and asymmetric appearance of separation bubbles on both sides of the circular cylinder. The asymmetric formation of separation bubbles is the origin of lift. The Reynolds number, Re = 3.6 x 10(exp 5), is appropriately called the critical Reynolds number for the drag coefficient of a circular cylinder.