Liquid Rocket Engines (LREs) represent a widespread technology in the space industry and are undergoing a deep innovation process in order to meet both the demanding requirements of performance, reliability and costs and the recently emerged issue of reusability. Crucial in the propulsion system design process is the thermal load characterization, being the engine operating life strongly dependant on the wall temperature. Concurrently a reliable modeling of the propellants is needed to properly describe their fluid-dynamic and reactive behavior inside engine components such as cooling channels, injectors and combustion chamber. This is of paramount importance when considering that propellants in LREs operate in a region referred to as "trans-critical", since they are stored at temperature below their critical values but operate in the combustion chamber and its cooling system at high pressure exceeding the critical point. In such a condition the mixture behavior deviates by the ideal model being dominated by real gas effects. Among the most recently proposed fuels, methane is showing many advantages over other commonly used hydrocarbons in terms of efficiency and storability easiness, however its fluid dynamics in proximity of the critical condition is still widely unknown, thus requiring further understanding and modeling.
This research project proposes the development of a solver capable of simulating the propellant turbulent flow and combustion inside the various engine components and the heat exchange with the solid walls, thus being predictive on the wall thermal loads. Simulation will be supported by an accurate thermophysical model describing high pressure turbulent flames and a near-wall treatment consistent with the LRE-like conditions.
Conjugate heat transfer of supercritical fluids in LRE-relevant conditions is state of the art problem. The present research project aims to be active support in the process of propulsion systems design and optimization, satisfying both the demand for CFD simulations of high pressure, turbulent and reactive flows inside rocket combustors, and the challenging request to predict the thermal behavior of LRE thrust chambers.
The first novelty of the proposed project consists in the suggested numerical framework: flamelet-based method are well posed in the low Mach approximation for the description of turbulent non-premixed combustion. Moreover this approach allows to efficiently model LRE relevant features as real-gas thermodynamics and non-adiabatic combustion [1]. Flamelet modeling combined with solid heat transfer description will provide a complete solver suitable both for high-fidelity simulations of subsystems and lower-order description of integrated engine, helping to understand the wall heat transfer mechanisms inside rocket combustion chambers. Concurrently the construction of a DNS database will provide physical insight on the phenomena characterizing super/trans-critical flames [2], constituting a reference for validation and development of lower-order models.
Bibliography
[1] P. E. Lapenna, G.Indelicato, R. Lamioni, F. Creta, "Modeling the equation of state using a flamelet approach in LRE-like conditions", Acta Astronautica, Vol. 158, 2019, pp. 460469.
[2] P. E. Lapenna, F. Creta, "Direct Numerical Simulation of Transcritical Jets at Moderate Reynolds Number", AIAA Journal, Vol. 57 (6), pp. 2254-2263, 2019.