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.
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