Drag crisis instability of a slender pole: A case study

The circular cylinder is the classic shape that has received the most attention in the literature. This is due in part to its widespread use as a structural form where flow-induced vibrations are a concern ranging from cooling towers and chimney stacks to risers in offshore oil drilling operations to heat exchanger tube arrays. It is also due to the fact that the seemingly benign shape poses the most difficulty from an experimental or design point of view because of the well-known sensitivity of the aerodynamics to factors such and turbulence, vibration amplitude and most importantly, Reynolds number (Re). This paper presents a case study of an aeroelastic instability unique to the circular cylinder due to the dependence of the drag loading on Re. Specifically, the change in drag coefficient through transition Reynolds numbers referred to as the drag crisis. While known as a theoretical instability for some time, the authors are not aware of another case of the drag crisis instability in air flow.