Flow induced oscillations of two interfering circular cylinders

Abstract

Flow interference between two circular cylinders in various arrangements imposes continuous and discontinuous changes in vortex shedding. The resulting oscillations induced by the vortex shedding are considerably modified by and strongly depend on the arrangement of the two cylinders. A systematic classification of flow interference regimes is linked to the observed vortex shedding responses for a wide range of arrangements. The discontinuous change of flow regimes in some arrangements can excite and maintain large amplitude oscillations beyond a certain critical velocity. The critical velocity and magnitude of oscillation strongly depends on the initial location and subsequent displacement of the cylinder by the fluid-elastic forces. The wide variety of fluid-elastic responses can be categorized at least into three characteristic types for two cylinders with identical properties: (1) instability rapidly builds up to extremely large amplitude predominantly in the streamwise direction; (2) instability slowly builds up amplitude to a certain level, the oscillations being mostly in the streamwise direction; (3) instability gradually builds up to large amplitude predominantly in the transverse direction. It has been found that all types of the fluid-elastic oscillations were related to the regions of interference.