Observations of the Oscillatory Behavior of a Confined Ring Vortex

Ring chambers with annular inflow and outflow through a radial exit tube find wide application in axial-flow turbomachinery as exit chambers to collect and divert the throughflow off-axis. Visual observations and detailed measurements of the flow in an idealized model exit chamber reveal that the flow in the ring is dominated by the vortex generated by the annular inflow. Coriolis forces, arising as a result of the longitudinal curvature imposed on the basic swirling flow, cause the vortex to adopt a helical form within the confines of the ring. Also, an interaction between the two ends of the vortex within the exit tube gives rise to oscillations of the flow which are strongly periodic for certain values of the ratio of the annular width t to the ring radius R. The periodic oscillations are characterized by a constant Strouhal number//?/ ^«0.03, where/is the fundamental frequency and V the inflow velocity. Although the flow oscillations can be suppressed by installing a splitter plate in the exit tube, when the vortex ends are separated and so cannot interact, the splitter plate has no direct influence on the vortex, the spatial structure of which is largely unaltered.