Large Eddy Simulation of Flow Dynamics and Flame Behavior in the NASA Energy Efficient Engine Annular Combustor

Abstract This study investigates unsteady flow, mixing, and combustion in a 360-deg full annular combustor, with a particular focus on the NASA energy efficient engine (E3), using large eddy simulation (LES). A fully compressible Navier–Stokes solver, combined with a flamelet progress variable approach and Lagrangian particle tracking, simulates the fuel spray breakup, vaporization, and ignition. The investigation starts by analyzing the unsteady, nonreacting flowfield to assess the role of the central recirculation zone in fuel-air mixing and flame stabilization. Proper orthogonal decomposition (POD) analysis revealed that the flowfield is dominated by energetic modes linked to large-scale structures like recirculation zones. These modes identify primary flow patterns and their interactions with injected dilution air, driving the unsteady behavior of the system. LES results for the multiburner combustor shape factor are also compared with experimental data and prior LES studies, showing good agreement. Spectral analysis also identifies the longitudinal mode as the primary acoustic mode, influenced by the annular shape of the combustor. In addition, the study traced the origin of hot streaks at the combustor exit to the pilot dome, where inefficient mixing of burned gases and dilution air occurs. The flame index (FI) analysis identified a mix of premixed and nonpremixed combustion regimes, offering valuable insights into the combustion process. This research advances the understanding of the combustion mechanisms that govern the performance and efficiency of real-world annular combustors.