Ricerc@Sapienza

The main focus of this research is on the fluid-dynamic phenomena involved in a space transportation system design process. More specifically, a major improvement of the predictive and surrogate models generation capabilities is expected in the fields detailed in the following. 1) External flow of space launcher characterization in the lift-off and ascent phases will be carried out by means of Reynolds Averaged Navier Stokes (RANS) approaches for turbulent three-dimensional flows. 2) The hypersonic flows for atmospheric re-entry description will be attained via density-based RANS approaches, while finite rate chemical kinetics will be employed for the dissociative processes taking place under such conditions. The solutions are computed using a commercial code coupled with an "in-house" mesh-adapting procedure applied in the shock region to align the mesh to the bow shock. 3) The interaction between turbulent motions and chemical reaction in Liquid Rocket Engines (LRE) will be inquired following a variable fidelity approach. The entire chamber will be modeled via RANS approaches coupled with passive scalar based approaches, while a hi-fidelity direct numerical simulation (DNS) approaches will be employed for a detailed a-priory study of interactions between turbulent motions and chemical reactions. 4) The combustion chamber characterization in Solid Rocket Motors (SRM), and Hybrid Rocket Engines (HRE) will include detailed analysis of phenomena like fluid-surface interaction, radiation, entrainment, pyrolysis, turbulent mixing and combustion of supercritical paraffin. Direct numerical simulations, will be designed to provide a better understanding of the underlying physics and results will be used to develop, improve, calibrate and validate models for RANS computations. 5) The liquid spray injection, atomization, vaporization and combustion in Liquid Rocket Engines (LRE) will be addressed resorting to a variable fidelity approach. The liquid break-up and atomization will be inquired by a volume of fluid (VOF) approach implemented in a direct numerical simulation framework. The dynamics of the ensuing droplets will be tracked by a Lagrangian approach for the disperse phase. 6) The estimation of the wall heat fluxes and cooling system of LRE is one of the most critical aspects that has to be faced since an over-sized cooling system leads detrimental effects on the engine performances, especially for new fuels, such as methane, whose cooling properties still require to be determined. Reduced 1D and 2D models and RANS-based approaches will be exploited for the design optimization process [8], where parametric studies can be easily carried out to assess the effects of the most important design parameters, such as the characteristic dimension of the ribs, evaluating also the performance of different wall materials. 7) Wall flows characterization in cooling channels of LRE is a key aspect in improving engine performance, hence an high fidelity DNS campaign, taking into account supercritical equation of state and transport properties, will be carried out to inquire the basic physics undergoing the wall heat transfer and to gain insights aimed at the fine tuning of the reduced model generation. 8) Shock-wave oscillations in overexpanded nobles during the sea-level startup produce dynamic side-loads that reduce the safe life of the engine and can lead to a failure of the nozzle structure. The self-excited shock wave oscillations in three-dimensional overexpanded nozzles turbulent flow will be investigated by means of Detached Eddy Simulations (DES). 9) Thermo-chemical model reduction for propulsive applications will allow to strongly reduce the computational burden arising from the need of taking into account chemical kinetics, playing a dominant role in reactive flow inside the thrust chambers as well as in the hypersonic flows typical of atmospheric re-entry. The employed techniques rely on CSP methods and allow for the generation simplified/reduced chemical mechanisms tailored on the specific needs on a case-by-case basis.