Floating ring bearings (FRBs) are widely used in automobile turbochargers. However, there is no satisfying explanation of phenomenon that ring rotation speed levels off when the shaft speed reaches a certain value under low oil-supplied pressure condition. The traditional opinion that effective viscosity decreases with increasing temperature cannot completely explain this phenomenon. In this study, the air entrainment effect is introduced and evaluated using computational fluid dynamics (CFD). CFD results considering air entrainment, viscous heating, and heat transfer are compared with experimental results to evaluate each effect. The decrease in effective viscosity as a result of air–oil–thermal coupling effect is the mechanism behind the abovementioned phenomenon. This study provides calculated data and visual results of the air entrainment in low oil-supplied pressure FRB.

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