Computational Fluid Dynamics and Experimental Visualization of Time-Variable Air Flow Pattern Inside Hard Disk Drives

The time-variable air flow pattern inside hard disk drives (HDDs) was analyzed using computational fluid dynamics (CFD) and experimental flow visualization. The existence of a rotating polygonal flow pattern inside an actual HDD was directly confirmed both through simulation and experiment for the first time. Even though earlier studies reported time-invariant polygonal flow pattern inside fully shrouded co-rotating disks, we found that the polygonal flow pattern varied its polygonal number repeatedly with time in not fully shrouded actual HDD. Triangular, tetragonal, pentagonal, and hexagonal flow patterns were observed both in simulation and experimental visualization. We also observed peaks in the power spectrum density of the simulated air velocity and these corresponded to the polygonal flow patterns. It was also found that each of these frequencies basically coincides with the frequency expected by the relation between the polygonal number and the vortex frequency which has been reported by earlier studies using fully shrouded co-rotating disks.