Liquid oxygen turbopumps are an important component of rocket engines. The instability induced by cavitation flow in turbopumps has received considerable attention because of thermodynamic effects. In this study, unsteady numerical simulations of a turbopump with thermodynamic effects were performed. The frequency composition and source of pressure fluctuations in a turbopump were analyzed, and the difference in pressure fluctuations with/without thermodynamic effects was revealed. The results showed that the pressure fluctuations were mainly caused by the interaction between the impeller and diffuser, and the thermodynamic effects slightly increased the amplitudes of the characteristic frequencies. In addition, in the inducer and impeller, three characteristic frequencies (4.089fn, 2.519fn, and 3.238fn, where fn is the rotational frequency) were confirmed. Analyses revealed that the 4.089fn was due to the periodic shedding of cavitation structures on the suction surfaces at the inducer outlet, 2.519fn was induced by the periodic occurrence and collapse of cavitation on the suction surfaces at the impeller inlet; and 3.238fn was from the periodic shedding of cavitation structures on the suction surfaces at the impeller middle blades. The existence of thermodynamic effects decreased the frequency of cavitation shedding and increased the frequency of the periodic occurrence and collapse of cavitation.

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Dynamic gas-liquid mass transfer behaviors are widely encountered in the chemical, environmental, and engineering fields. Referring to the Singhal full cavitation model, Henry's law, and Zhou's experiments, we innovatively developed a computational model for dissolved and released mass-transfer to revolutionize the independent unidirectional gas-to-liquid or liquid-to-gas theory. From a new perspective, coupled dissolution and evolution mechanisms were defined similar to how condensation and evaporation were redefined, where dissolution and release mass-transfer prediction methods that can be applied to three-dimensional calculations were integrated for the first time. The dissolved gas saturation concentration was the criterion for determining the direction of mass transfer. According to the theoretical derivation, the driving forces behind the dissolution and evolution are the remaining undissolved gas and real-time solution concentration, respectively. We confirmed the validity of the proposed dynamic model using an unsteady simulation after a grid independence study and an experimental verification of dissolved oxygen concentration in plug-discharge flow. The difference in dissolved oxygen concentration between simulations of this computational model and experiments could be low as 2.0%. A higher dissolved oxygen concentration was distributed in the flow separation and throat gas-liquid blocking zones, indicating that a surge in the flow velocity led to an increased mass transfer rate. In addition, a parametric study was conducted to consider the impact of the oxygen volume fraction and initial dissolved oxygen concentration on the real-time concentration.

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