Titolo della tesi: Modeling and Simulations of High-Pressure Injection in Aerospace Propulsion Systems
This thesis is dedicated to the numerical modeling and simulation of aerospace propulsion devices based on combustion and operating under high-pressure thermodynamic conditions. Several injection regimes are considered, ranging from sub- and near-critical pressure conditions to supercritical regimes. The numerical models used to describe the behavior of fluids under extreme thermodynamic conditions are discussed, introducing real-fluid equations of state for the numerical simulation 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.
First, 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 evaporation 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 on a subcritical turbulent spray flame relevant to liquid rocket engine applications will be addressed.
Several approaches are proposed to investigate supercritical pressure injection. The implementation of a tabulated pressure-based solver for highly stratified flows, addressing both non-reacting and reacting flows, is discussed and improvements are proposed 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.