This work deals with an investigation on real gas effects of underexpanded hydrogen jets in airbreathing engines for flight propulsion. This subject is very important for the optimization of the engine performance, for the reduction of emissions and also for safety reasons, in the case of sudden leaks from a high-pressure hydrogen containment vessel [1, 2]. In this work, the assumption of thermally perfect gas is considered and compared with two real gas models to analyse the influence of real gas condition on the complex structure of underexpanded jets, due to the presence of Mach disks, barrel shocks, expansion waves and reflected shocks [3-5]. The results show that the use of a real gas equation of state noticeably affects the flow-field simulation. The extent of the real gas modelling on the flow structure has proven to be strongly dependent on the thermodynamic conditions not only of the injected hydrogen, but also of the ambient air in which the jet penetrates. In fact, in the case of a high temperature hydrogen injection, the results, in terms of temperature and Mach number distributions, seem to be affected by the real gas assumption. Specifically, differences in temperature profiles between the ideal gas law and real gas state equations reach values up to 8%.
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