SECTIONAL LIFT FORCES FOR AN OSCILLATING CIRCULAR-CYLINDER IN SMOOTH AND TURBULENT FLOWS

Measurements of sectional lift forces are presented that were obtained using a circular cylinder with forced cross-flow oscillation in smoot h and turbulent wind tunnel flows at a Reynolds number of 1.6 x 10(5). Maximum oscillation amplitudes were 3% of diameter. By employing vari able-frequency forcing, the dimensionless oscillation frequency could be altered while the Reynolds number was held constant. With six trans ducers set out equispaced along the cylinder span it was possible to e stimate spanwise correlation of lift based on simultaneous measurement s, in addition to sectional lift coefficients. Decomposition of lift f orces into components correlated and uncorrelated with cylinder motion indicated that it was reasonable to assume that the uncorrelated comp onent was unaffected by cylinder motion and that the observed increase in spanwise correlation of lift could be accounted for by the motion- correlated component. For smooth Bow, examination of the magnitude and phase angle of lift force showed that lock-in was an intermittent occ urrence at the amplitudes of motion employed. Motion-correlated forces were found to be less significant in turbulent flows, with changes in oscillation frequencies producing little observable effect. (C) 1997 Academic Press Limited.