Unsteady Flow in the Obstructed Space Between Disks Corotating in a Cylindrical Enclosure

Abstract

Time-resolved measurements of the circumferential velocity component were obtained with a laser-Doppler velocimeter in the space between the center pair of four disks corotating in air in an axisymmetric cylindrical enclosure. The separate influences on the flow of two obstructions of similar shapes but having different lengths were investigated. The results show that both obstructions significantly alter the mean and rms distributions of velocity in quantitatively different but qualitatively similar ways. Both obstructions also alter the characteristic frequencies of flow oscillations associated with large scale motions present in the flow, apparently of the type that arise in unobstructed configurations. The measurements suggest that an obstruction can induce bimodal states of motion over frequency ranges that depend on the obstruction’s length. The presence of an obstruction increases the strength of the cross-stream secondary motion in the inter-disk space by redirecting fluid moving in the circumferential direction towards the radial direction. While this reduced the magnitude of the velocity deficit in the obstruction wake, for the cases investigated the flow did not recover within one revolution from the effects of either obstruction.

A Study on the Efficacy of Flow Mitigation Devices in Hard Disk Drives

“…They primarily reported mean and RMS values of circumferential velocities and the corresponding frequency content. Usry et al [9] also conclude that once the flow separates by flowing over the obstruction, "the flow does not recover within one revolution from the effects of the obstruction. "…”

“…10, the flow field is similar to M0, except that the upstream spoiler acts as another source of generation of turbulent eddies. The eddies shed from the top and bottom edges cause added velocity fluctuations in the upstream portion of the flow field (see (9) in Fig. 10).…”

“…Several authors [7]- [9] performed several laser-Doppler velocimetry experiments of rotating disks with and without an obstruction. They primarily reported mean and RMS values of circumferential velocities and the corresponding frequency content.…”

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

“…Using a laser Doppler velocimeter (LDV) technique, Usry et al (1993) obtained the circumferential velocity and corresponding RMS for the flow within a pair of corotating disks enclosed by a cylindrical shroud. Two obstructions geometrically similar with a taper toward the rotating center, but having different lengths were used.…”

Numerical analysis of off-track vibration of head gimbal assembly in hard disk drive caused by the airflow

“…The studies conducted by Abrahamson et al [3,4] revealed that the flow structures generated by the arm are dissipated in a short circumferential distance in the wake of arm. Usry et al [5] observed that the presence of an arm reinforces the cross-stream secondary flow in the radial direction. Gross [6] reported that the profile of arm leading edge has a significant effect on the flow velocity fluctuations measured in the vicinity of arm tip.…”