Numerical Simulation of Inlet Void Fraction Affecting Oil-gas Two-phase Flow Characteristics in 90° Elbows

Air can have an adverse effect on the performance of an aero-engine lubrication system. A numerical analysis was conducted to explore the influence of inlet void fraction and pipe layout on the characteristics of oil-gas two-phase flow in a 90° elbow. The pipes were arranged horizontally and vertically with inlet void fractions of 0.05-0.15. The laws governing flow velocity, void fraction, and pressure along the pipe were determined separately. The results revealed the formation of large-scale vortices with high gas volume fractions inside both types of elbows, which exacerbate oil-gas separation and cause additional head loss. The maximum pressure drop was observed at approximately one pipe diameter downstream of the elbow outlet, which initially increases with the inlet void fraction and then gradually stabilizes. Asymmetric secondary flow vortices in the horizontal elbow were found to enhance oil-gas separation and accelerate lubricating oil to greater extent than in a vertical elbow under the same conditions. Consequently, the maximum pressure drop caused by flowing through the horizontal elbow is higher than that in the vertical elbow.