Experimental Investigation on the Stability of Parallel and Oblique Plates as Suppressors of Vortex-Induced Vibration

Abstract

Experiments have been carried out on models of free-to-rotate parallel and oblique plates fitted to a rigid section of circular cylinder to investigate the effect of plate length and oblique angle on the stability of this type of VIV (vortex-induced vibration) suppressor. Measurements of the dynamic response and trajectories of motion are presented for models with low mass and damping which are free to respond in the cross-flow and streamwise directions. It is shown that, depending on a combination of geometric parameters — such as plate length, plate angle and gap between plates and cylinder — devices might not be able to completely suppress VIV for the whole range of reduced velocities investigated. Plates with larger oblique angles turned to be less stable than parallel plates and induced high-amplitude vibrations for some specific reduced velocities. An undesirable steady lateral force was also observed to occur for all configurations and might be related to the existence of a large gap and oblique angles. Systems may present streamwise vibration due to strong flow separation and reattachment on the outer surface of plates with large oblique angles. Large angles may also increase drag. Experiments with a plain cylinder in the Reynolds number range from 3,000 to 20,000 have been performed to serve as reference. Reduced velocity was varied between 2 and 13.