In the present numerical study, implicit large eddy simulations (LES) of non-reacting multi-components mixing processes of cryogenic nitrogen and n-dodecane fuel injections under transcritical and supercritical conditions are carried out, using a modified reacting flow solver, originally available in the open source software OpenFOAM®. To this end, the Peng-Robinson (PR) cubic equation of state (EOS) is considered and the solver is modified to account for the real-fluid thermodynamics. At high pressure conditions, the variable transport properties such as dynamic viscosity and thermal conductivity are accurately computed using the Chung transport model. To deal with the multicomponent species mixing, molar averaged homogeneous classical mixing rules are used. For the velocity–pressure coupling, a PIMPLE based compressible algorithm is employed. For both cryogenic and non-cryogenic fuel injections, qualitative and quantitative analyses are performed, and the results show significant effects of the chamber pressure on the mixing processes and entrainment rates. The capability of the proposed numerical model to handle multicomponent species mixing with real-fluid thermophysical properties is demonstrated, in both supercritical and transcritical regimes.
Large-eddy simulations (LES) of hydrogen jets under highly under-expanded conditions are carried out. Computational fluid dynamics (CFD) analysis appears extremely useful to fully understand and optimize the hydrogen injection process, like in internal combustion engines. This work aims to analyze hydrogen high-pressure injection in the near-nozzle region, investigating the formation process and the structure of the Mach disks and the transition to turbulent jets, for nozzle pressure ratios (NPR) of 5.8 and 30. A real fluid model is utilized and compared against the simpler ideal gas model, for injections into an ambient pressure environment. Furthermore, hydrogen-air mixing evolution is investigated in the far-field region. Average quantities obtained from statistical analysis on LES simulations are compared with available data. The near nozzle region, except for the initial transient part, is better captured by accurate spatial discretization methods, while properly predicting far-field effects, like turbulence and acoustic effects, seems to be mostly related to time discretization schemes.
Complexity behind physical phenomena of supercritical and transcritical jet flows, still leaves an ambiguous understanding of such widespread technology, with applications ranging from diesel and liquid rocket engines to gas turbines. In this present numerical study, a new open-source CFD model construction is presented and validated using a liquid-rocket benchmark comprised of liquid-oxygen (LOX) and gaseous-hydrogen (H2) streams. Mixing process of liquid oxygenhydrogen streams under liquid rocket engine (LRE) relevant conditions is scrutinized using the pressure-based solution framework implemented in the versatile computation platform Open-FOAM. The model accounts for real fluid thermodynamics and transport properties, making use of the cubic Peng-Robinson equation of state (PR-EOS) and the Chung transport model. The solver capability to capture the mixing layer between the two separated streams is discussed as well as its capability to predict with adequate accuracy the thermophysical quantities. Following the thorough validation, a comparison of the contribution of the accurate laminar transport properties vs. the large eddy simulation (LES) subgrid scale (sgs) turbulent values is conducted in order to assess the relative importance of the turbulent viscosity. By means of an assessment of the pressure-based numerical framework with available data in the literature, this work contributes to a better understanding of well resolved simulations. In addition, it enables the further development of a real fluid pressure-based multi-species solver as an open-source code.
The injections of cryogenic and non-cryogenic fluids in a supercritical environment, respectively, liquid N2 into gaseous N2 and n-dodecane into gaseous N2, 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.
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