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

The adoption of lean burn combustion to limit NOx emissions of modern aero-engines imposes a drastic reduction of air dedicated to cooling combustor dome and liners. In the latest years many aero-engine manufacturers are hence implementing effusion cooling, which provides uniform protection on the hot side of the liner and significant heat removal within the perforation. With an industrial perspective, the development of such components is usually carried out with different strategies depending on the level of accuracy required in the design phase involved (i.e preliminary or detailed). In the collaboration between GE Avio and University of Florence, the preliminary design of these devices is carried out with Therm1D, an in-house thermal flow-network solver based on the 1D correlative approach proposed by Lefebvre. This strategy, however, is not capable of taking into account the complexity of the three-dimensional nature of the flow field and the interaction between swirling flow and liner cooling, making necessary the use of Computational Fluid Dynamics (CFD) in the most advanced phases of the design process. Nevertheless, notwithstanding the increasing popularity of CFD, even a RANS simulation of a single sector of an annular combustor still presents a challenge, when the cooling system is taken into account. This issue becomes more critical in case of modern effusion cooled combustors, which may contain thousands of holes for each sector. With the aim of of increasing the fidelity of the prediction, keeping in mind the industrial needs for limited computational efforts, a new tool has been developed: Therm3D. This approach involves the CFD simulation of the combustor flametube by modelling effusion cooling with point mass sources, whereas the fluid dynamic prediction of the remaining part is fulfilled exploiting the equivalent flow-network solver implemented in Therm1D, which provides the estimation of flow split and cold side heat loads. The solution is coupled with two separate calculations aimed at solving flame radiation and heat conduction within the metal. This paper describes the main findings of the application of Therm3D to a lean annular combustor. The results obtained have been compared to experimental data and the above mentioned numerical tools employed during the design process.