A5.3 - Velocity Measurements of Gap Flows at a Computer Hard Disk Model

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A5 - Flow Sensors II
J. Czarske, L. Büttner, K. Shirai - Technische Universität Dresden (Germany), S. Obi - Keio University, Yokohama (Japan)
123 - 128


The gap flow in the tip clearance of a hard disk drive model has been investigated with optical measurment techniques. The flow was driven by co-rotating disks inside a cylindrical enclosure in order to simulate a hard disk drive for data storage devices. The main focus of the investigation was the understanding of the complex flow behaviors in the narrow region between the disk tip and the outer shroud wall, which is supposed to be one of the causes of flow induced vibrations of the disks. Experiments in the past have never been able to examine the flow in this region due to the lack of the spatial resolution of sensors. In the present investigation, the flow velocity in the tip clearance region was examined at four different conditions containting two different dimensions of the tip clearances and the shapes of the shroud walls with and without ribs. The velocity measurements were carried out both with a conventional laser Doppler velocimetry and a laser Doppler velocity profile sensor with a spatial resolution in the micrometer range. The circumferential velocity component was evaluated along the axial and radial directions. The steep gradients of the mean velocity in the both directions were successfully captured with a high spatial resolution, which was achieved by the velocity profile sensor. It was found that the spatial resolution of a sensor has a significant influence on the resulting velocity statistics through spatial averaging process in measurements if the spatial resolution is not sufficient compared to that of the flow. The gap flow in the tip clearance region shows different flow behaviors depending on the tip clearance and the shroud shape. In the case of the flat shroud without ribs, when the tip clearance decreases, the boundary layers developing over the disk surfaces penetrate into the tip clerance region and interact with the one developing along the shroud wall. The interactions of these two boundary layers seem to be the source of the complex three-dimensional behaviors of the flow in
the tip clearance region. In the case of the ribbed shroud wall, the velocity fluctuation was found to increase in the tip clearance region, while it is reduced in the inter-rib region.