Effect of Helical Strakes on Hydrodynamic Forces on an 8-Shaped Oscillating Cylinder

摘要

The purpose of this paper is to clarify the effects of height and pitchrnof helical strakes on the VIV reduction efficiency, and to investigate thernhydrodynamic phenomena of an 8-shaped oscillating cylinder with andrnwithout helical strakes. Hydrodynamic force measurements of forced inlinernoscillating cylinders with helical strakes of various configurationsrnwere performed. These results showed that the helical strakes with thernheight of 0.06D and the pitch of 2.5D are most effective for reducingrnthe lift force in the present cases. Hydrodynamic force measurementsrnand flow visualizations of forced 8-shaped oscillating cylinders withrnand without helical strakes were also carried out. These resultsrnsuggested that the helical strakes with larger diameter, e.g. height =rn0.12D, are necessary to suppress the 8-shaped oscillation in the presentrncases, and a circulating flow, which induces an asymmetric vortexrnshedding, occurs around an 8-shaped oscillating cylinder without helicalrnstrakes.