Numerical Investigation of the Gravity Effects on Two-Phase Cryogenic Methane Flow in a 90° Bend Feed Pipe

Abstract The dynamic behaviour of liquid-gas methane two-phase flow within cryogenic feed systems is critical for advanced aerospace propulsion, particularly under different gravitational conditions encountered during spaceflight. This study presents a detailed numerical investigation of two-phase flow characteristics in a 90-degree bend feed pipe under Earth gravity and microgravity (10−4g) environments, considering two flow orientations: vertically upward (against gravity) and horizontally downward (along gravity). The Volume of Fluid (VOF) method was employed to capture the phase distribution, regime transitions, velocity evolution, and interfacial dynamics at superficial liquid velocities of 0.05 m/s and 0.1 m/s, with a fixed superficial gas velocity of 0.344 m/s. Flow features are analysed using volume fraction contours, probability density functions (PDFs), velocity magnitude profiles, streamline behaviour, and radial velocity distributions. The results reveal that in vertical upward flow, gravity hinders vapour progression, causes phase separation, and leads to lower outlet velocities. The PDF analyses support the identification of flow regimes, such as mist, annular, or core-annular, depending on the flow orientation and gravity level. The study demonstrates that gravity and flow direction have a significant impact on the development and performance of two-phase flow. These findings are instrumental for designing cryogenic propulsion, refuelling, and storage systems in terrestrial and microgravity environments, where precise control of phase behaviour is essential.