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Partial and Full Aerodynamic Bypass for a Disk Storage Device

IP.com Disclosure Number: IPCOM000023877D
Publication Date: 2004-Apr-01
Document File: 7 page(s) / 265K

Publishing Venue

The IP.com Prior Art Database

Abstract

This article presents an aerodynamic flow channeling geometry and arrangement that shields the HDD actuator/arm/slider and disk(s) from aerodynamic excitation (buffeting). The problem solved is the alleviation of of a strong and unsteady airflow present upstream of the actuator arm, suspension and slider assembly. One prevalent solution to the disk buffeting problem is tight shrouding of the disk pack. Another is (nearly) completely stripping the air from the disks and re-routing substantially all of it around the actuator. However, the latter requires room for channeling which is very difficult to obtain. Through careful design of an aerodynamic bypass that efficiently removes much of the flow energy upstream from the actuator, the arm, suspension and slider can be sheltered while providing an additional benefit in the form of enhanced cooling of the actuator coil. In particular, a pronounced corner in the shroud that provides a path for the airflow to exit tangentially from the disk pack.

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Partial and Full Aerodynamic Bypass for a Disk Storage Device

The core idea is an aerodynamic structure that diverts the bulk of the rotational flow energy away from the actuator arm. While this energy is largely dissipated, additional benefits are

1. Reduction or avoidance of trace flutter
2. Reduction of flow induced vibration of the disk by the arm wake
3. Enhanced cooling of the actuator coil.
a. Partial Bypass: It is obvious from figure 2 that this benefit can be attained without further modification.
b. Full Bypass: A slot, hole, or vent can be placed along the internal guiding wall near the VCM to achieve this benefit.

How it works: A large pressure buildup on the actuator arm shown in Figure 1 is generally accompanied by turbulent fluctuations which occupy a frequency band that is objectionable to the HDD servo system. We have found - using computational fluid dynamic simulations - that the flow diverter schemes shown in Figures 2 and 3 are effective in preventing large pressure buildup on the actuator arm. The pressure profiles in the mid-plane between two disks of both schemes are shown in Figures 4 and 5. Note the pressure scale: the dynamic pressure generated by corotating disks is of the order of the air density "rho" multiplied by the square of a characteristic velocity such as the product of the angular velocity "omega" and the disk radius "radius."

Centrifugal effects cause the pressure distribution among corotating disks to be roughly parabolic in the radial distance from the spindle axis. Thus one finds low pressure near the hub (small radius) and high pressure near the rim (large radius). This general pattern is locally disrupted by the arm, especially when there is no bypass channel. The flow field for the "end disks" in a disk pack are different because instead of a corotating disk, there is now a wall at which the flow velocity (because of the no-slip condition) is zero. the flow velocity in these end regions is roughly one half of what one observes between two disks for the same radius. For that reason, flow induced vibrations in the end region are less severe. Despite that, the flow velocities may still be sufficiently large to add to the overall flow induced vibrations.

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          FIGURE 1 Pressure Distribution of a Typical HDD

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     FIGURE 2 Partial Bypass Configuration

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     FIGURE 3 Full Bypass Configuration

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          FIGURE 4 Pressure Distribution of a Typical HDD with Partial Bypass

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          FIGURE 5...