An experimental study of three-dimensional vortical structures between co-rotating disks

Abstract

In this study, we experimentally investigate the flow between co-rotating disks in a stationary cylindrical enclosure. Here, the gap between disks is much narrower than disk radius. This flow is often non-axisymmetrical and complicated. This flow sometimes induces magnetic-head oscillations in disk storage devices of PCs. We carry out flow visualisations using a high-speed camera, and time-successive three-dimensional PIV (Particle Image Velocimetry) analyses of visualised pictures. We focus on the relation and combination of axial modes with circumferencial modes. Tested cases are two, that is, A (Re = 1.2 × 104 and δ = 0.12) and B (Re = 1.0 × 105 and δ = 0.20). Here, Re is the rotating Reynolds number, and δ is a non-dimensional gap. Case A is in axial mode II and circumferencial mode 8-9, and case B is in axial mode III and circumferencial mode 4. Axial modes are related with the symmetry of a pair of toroidal-vortical structures and circumferencial modes are related with the radial fluctuation of these structures as well as the solid-body-rotation core. As a result, in case A, the vortical structures are mainly influenced by axial mode (II) in the z direction, but not influenced by both axial mode (II) and circumferencial mode (8-9) in the r direction. In case B, the vortical structures are mainly influenced by axial mode (III), but influenced by circumferencial mode (4) in the r direction.