Effect of the cross-sectional shape of the recirculation channel on expulsion of air bubbles from FDBs used in HDD spindle motors

Abstract

This paper experimentally and numerically investigated the behavior of air bubbles in the oil lubricant of operating fluid dynamic bearings (FDBs) with a cross-sectional recirculation channel (RC). Experiments were performed to visually observe the behavior of trapped air bubbles in operating FDBs with crescent and circular cross-sectional RCs, respectively. Furthermore, a numerical study was carried out to investigate the phenomenon of air bubble expulsion from the FDB. The flow field of a FDB was calculated by the Navier-Stokes equation, continuity equation and volume of fluid (VOF) method. Results indicated that a crescent cross-sectional RC generates a larger pressure difference between the upper and lower regions of the RC and a faster flow velocity along the RC than a circular cross-sectional RC, because the former has larger wall shear stress than the latter, mainly due to a longer perimeter. Finally, we designed a novel RC that efficiently expels air bubbles.