Modeling and simulations of high-pressure injection in aerospace propulsion systems

This thesis is devoted to the numerical modeling and simulation of aerospace propulsion systems based on combustion and operating under high-pressure thermodynamic conditions. Several in- jection regimes, ranging from sub- and near-critical pressure conditions to supercritical states, are considered. The numerical models used to describe the behavior of fluids under extreme thermo- dynamic conditions are discussed, introducing real-fluid equations of state for the numerical simu- lation of reacting flows, then introducing the concept of vapor-liquid equilibrium thermodynamics to characterize both the multiphase equilibrium regime and interfacial phenomena, and discussing its application. Subcritical pressure injection phenomena are considered first, and the evaluation of non-ideal fluid modeling for droplet evaporation in jet-like conditions is addressed. This analysis aims to quantify the impact of a comprehensive framework for investigating the droplet evapora- tion process, including non-ideal fluid modeling, on both thermodynamic and transport properties, as well as the treatment of the high-pressure vapor-liquid equilibrium interface, and to further understand the actual role of the latter in practical applications. Then, using a combined Eulerian- Lagrangian and Bayesian uncertainty quantification framework, the influence of intrinsic modeling uncertainties on combustion observables in a subcritical turbulent spray flame relevant to liquid rocket engine applications is addressed. Several approaches are proposed to investigate supercrit- ical pressure injection. The development of a tabulated pressure-based solver for highly stratified flows, addressing both non-reacting and reacting flows, is discussed, and improvements are pro- posed to address liquid rocket engine relevant conditions. In this context, a high-fidelity simulation of the supercritical mixing layer is performed, and the framework architectures are validated against state-of-the-art solvers. A systematic analysis of the role of molecular diffusion modeling in high Reynolds number flows is then performed. Concurrently, highly resolved large eddy simulations of transcritical and doubly transcritical flames are presented. The goal is twofold: on the one hand, to provide high-fidelity simulations of the doubly transcritical case, which is of particular relevance to the community given the still limited studies on this peculiar case; on the other hand, to provide a consistent definition of the turbulent pseudo-boiling rate for the reacting mixture within a LES framework. The developed dataset is used to study the statistical properties of the mass transfer rate under pseudo-boiling conditions and its interplay within a turbulent flow.