Assessment of Scale-Resolved Computational Fluid Dynamics Methods for the Investigation of Lean Burn Spray Flames

摘要

Incoming standards on NO_x emissions are motivating many aero-engines manufacturers to adopt the lean burn combustion concept. However, several technological issues have to be faced in this transition, among which limited availability of air for cooling purpose and thermoacoustics phenomena. In this scenario, standard numerical design tools are not often capable of characterizing such devices. Thus, considering also the difficulties of experimental investigations in a highly pressurized and reactive environment, unsteady scale-resolved CFD methods are required to correctly understand the combustor performances. In this work, a set of scale-resolved simulations have been carried out on the Deutsches Zentrum fuer Luft- und Raumfahrt (DLR) generic single-sector combustor spray flame for which measurements both in nonreactive and reactive test conditions are available. Exploiting a two-phase Eulerian-Lagrangian approach combined with a flamelet generated manifold (FGM) combustion model, LES simulations have been performed in order to assess the potential improvements with respect to steady-state solutions. Additional comparisons have also been accomplished with scale-adaptive simulation (SAS) calculations based on eddy dissipation combustion model (EDM). The comparison with experimental results shows that the chosen unsteady strategies lead to a more physical description of reactive processes with respect to Reynolds-averaged Navier-Stokes (RANS) simulations. FGM model showed some limitations in reproducing the partially premixed nature of the flame, whereas SAS-EDM proved to be a robust modeling strategy within an industrial perspective. A new set of spray boundary conditions for liquid injection is also proposed whose reliability is proved through a detailed comparison against experimental data.