Numerical and Experimental Investigation on an Effusion-Cooled Lean Burn Aeronautical Combustor: Aerothermal Field and Emissions

Abstract

Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NOx and soot in particular). Its implementation, however, involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. Also, the conditions at the combustor exit are a concern, as high turbulence, residual swirl, and the impossibility to adjust the temperature profile with dilution holes determine a harsher environment for nozzle guide vanes. This work describes the final stages of the design of an aeronautical effusion-cooled lean burn combustor. Full annular tests were carried out to measure temperature profiles and emissions (CO and NOx) at the combustor exit. Different operating conditions of the ICAO cycle were tested, considering Idle, Cruise, Approach, and Take-off. Scale-adaptive simulations with the flamelet generated manifold (FGM) combustion model were performed to extend the validation of the employed computational fluid dynamics (CFD) methodology and to reproduce the experimental data in terms of radial temperature distribution factor (RTDF)/overall temperature distribution factor (OTDF) profiles as well as emission indexes (EIs). The satisfactory agreement paved the way to an exploitation of the methodology to provide a deeper understanding of the flow physics within the combustion chamber, highlighting the impact of the different operating conditions on flame, spray evolution, and pollutant formation.

Multiphysics Numerical Investigation of an Aeronautical Lean Burn Combustor

“…Measurement points were located in selected sectors at different angular positions and grouped to obtain a tangential distribution for a single ideal sector. A traverse system was used at the combustor exit to sample the gas emissions and analyse the temperature pattern (see Figure 3), which however are not the objective of this work and were better discussed in a previous work focused on the prediction of the aerothermal field with Scale-Adaptive Simulation (SAS) [25].…”

“…As above mentioned, scale resolution in SAS has not an explicit dependency on grid spacing. However, its adequacy in the prediction of aerothermal field was widely evaluated in [25] where a grid sensitive study was carried out. As in the near-wall region the SAS model behaves as a RANS k-ω SST model, to exploit a wall function approach [27] the mesh counts 3 prismatic layers at wall and a y+ in the range of applicability for this wall treatment.…”

“…The boundary conditions were set according to [25] for the convection problem and to [24] for the remaining simulations. Concerning convective domain mass flow rate and static pressure were prescribed, respectively, at the inlet and outlet boundaries shown in Figure 5.…”

“…The experimental measurements performed at the Central Institute of Aviation Motors (CIAM) on such combustor allowed to obtain valuable data at several operating conditions both in terms of pollutant emissions, wall temperature and exit temperature profile. On the same annular combustor steady analyses with the THERM3D tool were performed in [24] to predict metal temperature, whereas SRSs were adopted in [25] for an accurate characterization of aerothermal field in the flametube, with focus on profile temperature at exit and pollutant emissions. The results have revealed that Conjugate Heat Transfer can take advantage of a scale-resolving treatment of turbulence and this work tries to be the missed link between [24] and [25].…”

“…On the same annular combustor steady analyses with the THERM3D tool were performed in [24] to predict metal temperature, whereas SRSs were adopted in [25] for an accurate characterization of aerothermal field in the flametube, with focus on profile temperature at exit and pollutant emissions. The results have revealed that Conjugate Heat Transfer can take advantage of a scale-resolving treatment of turbulence and this work tries to be the missed link between [24] and [25]. To the authors' knowledge no works can be found in literature on multiphysics simulations of lean burn combustors relying on Scale Adaptive Simulation.…”