Recondensation behavior modeling in a liquid methane-oxygen common bulkhead tank by a modified level set method

Computational fluid dynamics is a vital method for discovering physical mechanisms behind experimental phenomenon. To simulate storage behaviors efficiently and accurately in cryogenic propellant tanks, a new approach that incorporated a modified level set method and the standard k-ε turbulence model was developed. The proposed simulation method provides a unified computational framework that eliminates the need for a two-step calculation process in the original level set method, while ensuring volume conversation by incorporating the effects of heat ingress and the associated variation in interface curvature. It was validated against experimental data for both an individual liquid oxygen tank and a nonadiabatic common bulkhead tank containing liquid oxygen and liquid methane on either side. In the common bulkhead tank, the maximum temperature gradient and self-pressurization rate were 75.90 K/m and 19.34 kPa/h, corresponding to only 33.53 % and 65.38 % of those in the individual tank. Notably, a unique re-condensation phenomenon was observed at the lower surface of the common bulkhead partition, which is absent in individual tanks. It enhances condensation of the boil-off gas and suppresses self-pressurization behavior. Additionally, a critical liquid oxygen filling ratio of 76 % was identified that significantly influences the no-venting storage duration of common bulkhead tanks. Unlike the individual tank, the maximum lossless storage duration in the common bulkhead tank increases with higher liquid oxygen filling ratios, with an 18.13 % extension observed once the threshold was exceeded. The methodology offers guidance for predicting the storage characteristics of cryogenic propellants in tanks.