Hydrodynamic damping of a cylinder at beta approximate to 10(6)

This paper describes delicate, but large-scale, experiments aimed at measur ing the hydrodynamic damping of a circular cylinder oscillating in still wa ter and transversely in a current. Attention is concentrated on the regime of very small Keulegan-Carpenter numbers, in which the drag coefficient is inversely proportional to the Keulegan-Carpenter number. Measurements in st ill water at beta = 650 000 and 1 250 000 point to drag coefficients about twice those appropriate to two-dimensional laminar flow, in common with ear lier measurements at beta approximate to 10(5). In the presence of a slowly varying transverse current (generated by placing the cylinder at the node of standing waves of long period), the damping increased with the reduced v elocity of the ambient flow at a rate that increased with the Reynolds numb er. (C) 2000 Academic Press.