Numerical Analysis of Fluid-Structure Interactions in an Air or Helium-Filled Hard Disk Drive

Kil, Sae Woong, Mechanical and Aerospace Engineering - School of Engineering and Applied Science, University of Virginia
Haj-Hariri, Hossein, Department of Mechanical and Aerospace Engineering, University of Virginia

From the advent, the HDD has been the most effective and important medium of data storage. To satisfy trends of the data storage industry, the design of the HDD has continued to evolve. The modern trend in the HDD tries to minimize the dimensions for better portability, and to maximize the data density on the disk surface for enhanced capacity. These trends require quite high positioning accuracy of Slider Suspension Units (SSU), which support the magnetic head. Another important demand is faster rotating speeds so that the data transfer time of the HDD can remain competitive with other storage devices such as flash memory. However, the increased rotating speed of the disk induces turbulent flow in the HDD and deteriorates the positioning accuracy of the SSU. Many investigations have tried to reduce the turbulent flow and the magnitude of the flow-induced vibration on the SSU by installing blockages upstream of the SSU to decrease the local turbulent flow. However, such geometrical modifications are ad hoc and have little basis in the underlying physics.
The goal of the present research is to reduce the flow-induced vibration of the SSU by changing the fluid medium inside the HDD. The fundamental nature of the flow field between the co-rotating disks is investigated in the presence of the actuator arm and the SSU. Helium is chosen as an alternative medium inside the HDD. The physical properties of helium decrease the fluid forces on the SSU and the turbulent kinetic energy around the SSU by stabilizing the flow field. To analyze the flow field in the space between the disks, numerical calculations were executed by employing commercial software ANSYS-CFX. To find a fundamental correlation between the flow oscillation and the vibration of the SSU at high rotating speeds, a FEM code (ANSYS) was fully coupled with ANSYS/CFX. By employing the coupled calculation technique, the underpinning physics of the SSU vibration is exposed. Also, it is demonstrated that the magnitude of the vibration is reduced substantially by using helium instead of air in the HDD.

PHD (Doctor of Philosophy)
Fluid-Structure Interaction, Flow-Induced Vibration, CFD, FEM, Coupled Analysis, Hard Disk Drive
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