Analyzing single and multicomponent supercritical jets using volume-based and mass-based numerical approaches

The injections of cryogenic and non-cryogenic fluids in a supercritical environment, respectively, liquid N-2 into gaseous N-2 and n-dodecane into gaseous N-2, are investigated. The two systems are analyzed under dynamic and thermal similarity (same reduced temperatures, reduced pressures, and Reynolds numbers) using the same simplified two-dimensional configuration for the totality of the simulations. This work contributes to provide insight into the interpretation of numerical studies on single- and multicomponent systems under supercritical conditions. A comprehensive comparison of the results obtained from two numerical approaches, based on the volume of fluid and on the homogeneous mixture assumption, making use of two distinct thermophysical and mixing rule frameworks, is presented. Results show very similar and consistent fluid mechanics and mass diffusion processes predicted by the two approaches, but different thermal behaviors for binary-species configurations. The two different mixing models are found to have the greatest impact on the temperature predictions. Also, isobaric-adiabatic mixing, which is obtained with the mass-based homogeneous approach, leads eventually to a larger extension of the predicted two-phase region. Such findings have large implications in energy systems operating at high pressure, where accurate local temperature predictions are crucial.