I am wondering about the drag coefficient for a flow past a cylinder. I am reading this article.
I understand why the drag is high to begin with (point 2), when the boundary layer separates and the recirculations appear, the pressure behind the cylinder (where the wakes are located) will drop, creating a drag. This is similar to what happens when vortices appear at the end of an airplane wing, the result is a drag force.
However, I am wondering about the following:
1) Why does the drag decrease as the Re goes up?
2) Why does the drag coefficient take a dive at point 5
3) Why does it rise after point 5?
The text doesn't really explain why the drag coefficient is increasing or decreasing.