Experimental study of the flow-structure interactions in an air- or helium-filled hard disk drive geometry

Abstract

The increased rotating speed of the hard disk drive (HDD) causes an unsteady flow field between each stack of disks and leads to flow induced vibration on the slider suspension unit (SSU). This flow induced vibration can reduce the positioning accuracy of the SSU and lead to failure to read or write data. Therefore, reduction of turbulence kinetic energy around the SSU is an important step to improve the performance of the HDD. Several modifications have been investigated in air to decrease the direct effect of unsteady flows on the SSU (e.g. spoiler, damper, or divider in the region upstream of the arm). However, these methods are not fundamental solutions for reducing the vibrations on the SSU. Since the HDDs currently in use are filled with air, helium was selected to compare the flow pattern due to the differing inertial property. To visualize the flow pattern, particle image velocimetry (PIV) measurements were performed at the inter-disk mid-plane between a pair of disks near the arm and the SSU. The geometry is an expanded 2× model simulating Seagate cheetah 2.5-inch drive. For both the air and the helium filled drives, measurements have been performed for two different locations of the SSU for two different angular velocities of 1,000 and 3,000 rpm, corresponding to 5,000 and 15,000 rpm in the commercial drive. The results reveal that the flow patterns of the air and the helium flow are quite similar. However, with respect to the turbulence intensity around the SSU, the helium flow shows a drastic decrease compared with that of the air flow, resulting in much reduced positioning errors. As such, helium-filled drives have merit and should be looked into.