Revisiting the Flow Instability of Shrouded Corotating Disk Systems

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Abstract In disk drive systems, flow-induced vibration, often attributed to turbulent fluid motion, presents a significant challenge due to its wide-ranging frequency spectra. Helium-filled enclosures have been introduced to mitigate this issue by reducing the force exerted by fluid motion, owing to the lower gas density compared to air. This density reduction leads to a decrease in the inertia force relative to the viscous force, lowering the Reynolds number by nearly an order of magnitude and resulting in an anticipated transition from turbulent to laminar flow. However, the transitional regime poses challenges, potentially causing intermittently alternating flow motion between turbulent and laminar states, characterized by velocity fluctuations of larger magnitude. Our experimental study involved a series of tests with a system comprising five 3.5-inch disks enclosed within a cylindrical casing. Varying the disk rotation speed from 600 rpm to 7200 rpm resulted in Reynolds numbers ranging from about 1 × 104 to 1 × 105. While air-filled configurations consistently exhibited fully turbulent flow, helium-filled setups demonstrated laminar characteristics at lower Reynolds numbers. Our findings suggest transitional behavior at intermediate Reynolds number ranges, indicating a shift from stable to unstable flow patterns. These observations underscore the potential challenges associated with helium-filled disk systems.

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