E-Mail: juergen.czarske[at]tu-dresden.de

Background and Research Purpose Hard disk drives (HDDs) are among the most widely spread data storage devices. The development of HDDs goes toward higher data densities and increased rotation speeds with a continuously growing demand for larger storage capacity and faster data access speed. On the other hand, the next generation of HDDs is expected to be smaller in size and to consume less energy. The distance between the read-and-write head and the disk surface reaches into the range of 10 nm for recently developed HDDs. The disk rotation entrains the surrounding air and lets three-dimensional complex flow structures develop in a HDD. The complex flow induces disk vibrations, which may lead irreparable damage to the disks. Many investigations have been reported on the disk vibrations or/and on the flow structures in a HDD, but the detailed mechanism of the flow-disk interaction remains still yet to be understood. The air flow in a HDD can be roughly divided into three different regions: inner, outer and shroud regions [1] as depicted in Fig. 1. Region I (0≤rd/R2≤0.4) is the “inner region ” where flow exhibits the solid body rotation (rd: the radial coordinate originating from the spindle exterior, R2: the disk radius). Region II (0.4≤rd/R2≤0.75) is the “outer region ” where distinct vortical structure is observed. Region III (0.75≤rd/R2) is the “shroud region ” where significant turbulent production occurs due to the strong shear at the shroud wall. Fig. 1: Sketch of the flow regions in a co-rotating disk system