MULTIPHYSICS NUMERICAL INVESTIGATION OF AN AERONAUTICAL LEAN BURN COMBUSTOR

摘要

The importance of the combustion chamber has been underestimated for years by aeroengine manufacturers that focused their research efforts mainly on other components, such as compressor and turbine, to improve the engine performance. Nevertheless, stricter requirements on pollutant emissions have contributed to increase the interest on combustor development and, nowadays, new design concepts are widely investigated. To meet the goals of ACARE FlightPath 2050 and future ICAO-CAEP standards one of the most promising results is provided by the Lean Burn technology. As this combustion mode is based on a lean Primary Zone, the air devoted to liner cooling is restricted and advanced cooling systems must be exploited to obtain higher overall effectiveness. The pushing trends of Turbine Inlet Temperature and Overall Pressure Ratio in modern aeroengine are not supported enough by the development of materials, thus making the research branch of liner cooling increasingly relevant. In this context, Computational Fluid Dynamics is able to predict the flow field and the complex interactions between the involved phenomena, supporting the design of modern Lean Burn combustors in all stages of the process. RANS approaches provide a solution of the problem with low computational cost, but can lack in accuracy when the flow unsteadiness dominates the fluid dynamics and the strong interactions, as in aeroengine combustors. Even if steady simulations can be easily employed in the preliminary design, their inaccuracy can be detrimental for an optimized combustor design and Scale-Resolving methods should be preferred, at least, in the final stages. Unfortunately, having to deal with a multiphysics problem as Conjugate Heat Transfer (CHT) in presence of radiation, these simulations can become computationally expensive and some numerical treatments are required to handle the wide range of time and space scales in an unsteady framework. In the present work the metal temperature distribution is investigated from a numerical perspective on a full annular aeronautical lean burn combustor operated at real conditions. For this purpose, the U-THERM3D multiphysics tool was developed in ANSYS Fluent and applied on the test case. The results are compared against RANS and experimental data to assess the tool capability to handle the CHT problem in the context of scale-resolving simulations.