Solid-Body Rotation and Implication of Secondary Flow Downstream the Obstruction and Partial Shroud of a Rotating Flow in an Enclosed Corotating System

Abstract

Corotating disk systems such as hard disk drives (HDDs) used for data storage, exhibit complex three-dimensional flow structures that affect head positioning accuracy and disk vibration. In this study, we experimentally investigated rotating flow in the inter-disk region of an HDD obstructed by an arm. We used two-dimensional, two-component Particle Image Velocimetry to measure velocity fields in cylindrical coordinates, varying the arm insertion depth between deep and shallow angles. Our results highlight the presence of a critical radius across all angles, with transition scales varying based on insertion depth. Shallow insertion was dominated by solid-body rotation towards the edge of the hub, whereas deep insertion was dominated by the sheared flow region towards the edge of the disk. Solid-body rotation is fully developed at different downstream locations of the inserted arm for both deep and shallow insertion angles. Implication of centrifugal secondary flow occurred downstream and upstream regions of the inserted arm. Even though the Reynolds number remains in the transitional regime, some elevated strain and Reynolds stresses remained localized near the shroud opening and the vicinity of the inserted arm. Turbulent kinetic energy decayed rapidly downstream, which indicates that the flow is not fully turbulent but transitional and predominantly shear driven. This underscores the operating conditions of helium-filled systems, known to operate predominantly in the laminar-to-transitional flow regime due to the low density of helium compared to air. The localized turbulence has not been reported in previously simplified axisymmetric studies.