A PIV study of co-rotating disks flow in a fixed cylindrical enclosure

This study investigates the coherent flow between enclosed co-rotating disks using flow visualization and particle image velocimetry (PIV). To simulate the 3.5-inch hard disks the tested disks have a diameter of 275 mm and a gap-to-disk radius ratio of 0.09. In the flow measurements the Reynolds number is fixed at Re = 5.25 × 105 corresponding to a disk rotating speed of 12,000 rpm. The rotation speed and disk space selected above is for the next generation hard disk consideration, and the related parameters are determined through the Reynolds dynamic similarity Re(model,water30°C)=Re(prototype,air30°C). The results show that the flow between the disks can be characterized by eight sub-flow regions: namely 1st solid body rotation region, 2nd large-scale vortex structure region, 3rd detached shear layer region, 4th boundary layer region, 5th core region, 6th Ekman layer region, 7th Stewartson layer region, and 8th shroud shear layer region. Among these sub-flow regions the 5th to 7th flow regimes are not identified previously. In addition, the additional measurements of the circumferential velocity component in the 5th core region reveal that a pair of circular flow structure acts like an annular chain to surround the 2nd sub-region large-scale vortex. This finding is also not reported in the literature. Moreover, the present PIV phase velocity measurements provide the physical explanation of the cyclic variation in the 1st solid body rotation region reported previously by our Laser Doppler Velocimetry spectra measurements.