Steady and unsteady loading on a roughened circular cylinder at Reynolds numbers up to 900,000

This paper describes steady and unsteady loading in incompressible flow on a roughened circular cylinder in crossflow in the Reynolds number range from 50,000 to 900,000. The experiments were conducted on a cylinder of 38 mm diameter with aspect ratio 10. Measurements were made in smooth flow and in two levels of turbulence. Dynamic lift and drag measurements were made via two high-frequency force balances mounted at the ends of the model. The results demonstrate that with the level of roughness employed in this investigation, strong coherent shedding re-emerges in smooth flow for Reynolds numbers in excess of 750,000, whereas in smooth flow such shedding re-commences only for Reynolds numbers in excess of several million. It is also shown that turbulence serves to decrease the Reynolds number at which coherent shedding re-commences.