Two-dimensional topology analysis on the complex flow driven by corotating disks mounted in a non-axisymmetric enclosure

We have investigated fluid flow in a hard disk drive (HDD) with particle image velocimetry (PIV). Corotating disks mounted in an enclosure creates a three-dimensional unstable flow. The unstable flow results in errors in positioning the magnetic head that reads and writes data. We observed the flow through visualization and conducted measurements of flow velocities based on PIV performed in a simplified experimental HDD model. The refractive index of the working fluid was matched to that of the model made of poly methyl methacrylate (PMMA). We divided the flow into four quadrants and acquired particle image sets. Some of the flow statistics are coordinate-dependent and difficult to interpret the pure mechanism of the flow. In this study, tensor invariants were calculated as coordinate-independent statistics at the evaluation. We used velocity data obtained in a two-dimensional PIV and calculated invariance coefficients. The critical points were classified into five flow patterns based on the signs of the similarity invariant coefficients. The larger the arm insertion angle, the greater the obstruction to flow, so the instability factor was stronger in a quadrant containing the arm. The complex flow around the shroud opening confirmed the spirally spreading flow.