Phd in AERONAUTICS AND SPACE ENGINEERING

Thesis title: Multi-physics thermal characterization of rocket combustion chambers

This thesis is devoted to the numerical modeling and thermal characterization of technological devices based on combustion and operating under severe thermodynamic conditions. Several approaches are proposed throughout the thesis, sharing the same tabulated chemistry approach for the turbulent combustion modeling and the implementation in Unsteady Reynolds Averaged Navier-Stokes settings. First, single-region solvers will be discussed, dealing only with the modeling of the fluid domain. This approach is selected to collect a significant amount of data at a reasonable computational cost, allowing therefore parametric investigations and the development of data-driven models. Such analyses will be mainly devoted to the assessment of the effect of geometrical and injection parameters over the flow field and thermal load in a combustion chamber. The information gathered through the parametric analyses is then used as stepping stone for the preliminary implementation of a data-driven model for the thermal characterization of complex multi-injector geometries. The fidelity of the approach will be then increased including also the description of the heat transfer across different continua, through the simulation of multi-region test cases and hence introducing the coupled simulation of fluid and solid domains. In order to do so, a multi-region solver for Conjugate Heat Transfer is developed, featuring an interface boundary condition that guarantees temperature and heat flux continuity across the interfaces between an arbitrary number of solid and fluid domains. Also, an efficient coupling strategy aimed to the further reduction of the computational costs in convection-dominated phenomena is developed, based on the alternation between the two major approaches for coupled simulations found in the literature: directly coupled approach with Conjugate Heat Transfer and thermally chained simulations. Such a strategy will allow for the description of laboratory-scale test cases for the entire duration of the experimental runs. An extension of the solver will be also presented, accounting for pressure-dependence effects and allowing therefore the simulation of low-to-high Mach number flows such as the nozzle expansion downstream a combustion chamber. The main applications to which the thesis work is devoted are non-premixed, turbulent flames in combustion chambers under high pressure operating conditions, representative of the conditions encountered in Liquid Rocket Engines, simulated in both two-dimensional and three-dimensional settings. Nonetheless, a brief excursus on premixed injection modeling, relevant to gas turbine and aeronautical applications, will be given in the final section of the thesis, with particular reference to the peculiar challenges raised by this type of flames. More specifically, the topic of premixed hydrogen combustion will be tackled. Hydrogen flames present several modeling challenges, starting from the higher flame temperatures and laminar flame speeds compared to other conventional fuels, to the intrinsic instabilities that characterize premixed flames, that can be generated by either thermo-diffusive or hydrodynamic effects. A data-driven tabulated chemistry approach for premixed hydrogen combustion modeling will be proposed.