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Transitional air flow patterns at the mid-plane of gap between co-rotating disks in a stationary cylindrical enclosure are visualized under the acceleration condition of disks. The flow visualization is performed using olive oil particles with a laser sheet and CCD camera. On disk spinning-up, the transition flow patterns are clearly observed. The affect of magnitude of acceleration on the onset of transition and the relations of the number of vortex cells in fully turbulent regime of the flow in an outer region of the flow field to the rotating speed are also investigated. The centrifugal effect of particle is evaluated from the comparison with visualization results using hollow glass spheres.

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The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. The distribution of pressure disturbance on disks has relation to flow structure. To investigate the flow structure, the circumferential velocity was obtained using hot-wire measurements for the flow between the center pair of four disks of common radius R 2 co-rotating at angular velocity Ω in a fixed cylindrical enclosure. Disk radius is about 4 times larger than usual one of HDD to detect detail velocity profile. Hot-wire supporter acts as an obstruction in this case. The effects of rotating speed on large flow oscillation in outer region with hotwire supporter were investigated.