A 3D coupled approach for the thermal design of aero-engine combustor liners

The recent limitations imposed by ICAO-CAEP towards a drastic reduction of NOx emissions is driving the development of modern aeroengines towards the implementation of lean burn concept. The increased amount of air dedicated to the combustion process (up to 70%) involves several technological issues, including a signicant reduction of coolant available for the thermal management of combustor liners. This, from a design perspective, involves the continuous research for effective cooling schemes, such as effusion cooling, and the necessity of more accurate methodologies for the estimation of metal temperature, so as to properly assess the expected duration of hot gas path components. The flame stabilization through swirler characterized by large effective area leads to extended recirculating zones, which interact considerably with the liner cooling system. As highlighted in the first part of this dissertation, the impact on the near-wall flow field makes any consideration based on a correlative approach untrustworthy, demanding for more reliable evaluations through CFD analysis. Unfortunately, the application of effusion cooling entails a huge computational effort due to the high number of film cooling holes involved, therefore many approaches have been proposed in literature with the aim of modelling the coolant injection through mass sources. This work presents SAFE (Source based effusion model), a methodology for the CFD simulation of the entire combustor, which is based on the local coolant injection through point sources and a calculation of mass flow rate according to local flow conditions. A further step in reduction in the computational effort is represented by a different methodology, called Therm3D, which involves the simulation of the flame tube, whereas the solution of the remaining part of the combustor is fulfilled through the modelling of an equivalent flow network, which provides for the estimation of flow split and cold side heat loads. Ultimately, this work introduces innovative approaches for the CFD investigation of effusion cooled combustor, with a special focus on the metal temperature prediction. A model for the film cooling injection is proposed to overcome the issues related to the necessity of meshing the perforation, nevertheless several improvable aspects have been highlighted, pointing the way for further enhancements.