Assessment of Aero-Thermal Design Methodology for Effusion Cooled Lean Burn Annular Combustors

Increasingly stringent limitations imposed on aircraft engine emissions have led many manufacturers toward lean combustion technology, which involves a relevant increase in mass flow rate dedicated to primary combustion, leading as a consequence to a reduction of air dedicated to cooling of liners. One of the most promising cooling techniques in such conditions is represented by effusion cooling, which consists of an array of closely spaced discrete film cooling holes. This cooling method is based on a protective layer of cooling flow on the hot side of the liner, enhancing at the same time the heat removal within the holes. In the latest years many aero engine manufacturers have increased the research and technology investment on this combustion technology. Working in partnership with the University of Florence, specific component design tools and experimental techniques have been improved by Avio Aero for combustor gas turbine investigation. From a design perspective, CFD analysis has become a key tool up to the early stages of novel combustor design process, producing affordable direct 3D optimization of combustor aerodynamics. Nevertheless, a RANS simulation of even only 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 up to two thousand holes for the single sector. For this reason, many efforts have been devoted to develop methodologies based on film cooling modeling. Among the approaches published in the literature, models based on local sources represent a good compromise between simplicity and accuracy, with the capability to automatically perform a Conjugate Heat Transfer analysis. This type of methodology has been already defined and validated by the authors, with comparison on effusion cooled plates in terms of experimental overall effectiveness measurements as well as the application on a tubular combustor test case. In the context of this work, the proposed approach has been applied to the analysis of a lean annular combustor with the purpose of investigating pressure losses, flow split and metal temperature field. The results obtained have been compared to experimental data and different numerical tools exploited during the preliminary design of these devices.