Large Eddy Simulation of Turbulent Reacting Flow in a Pressurized Annular Combustor

Abstract Large eddy simulations (LES) are becoming increasingly popular in engineering to predict complex physical interactions governed by the temporal dynamics of the flow. In the context of propulsion systems with realistic combustors, LES is the ideal choice for modeling complex processes involving multiphase transport, vaporization, and reacting flow physics that span a wide range of scales. However, simulations of a full annular combustor have historically remained out of reach due to the steep cost associated with resolving the energetic scales in systems with such exceedingly complex geometries. Fortunately, with recent advances in supercomputing capabilities, such simulations are now possible and can be used to understand the underpinnings of combustion physics at scales that are often unavailable to experiments. Thus, the objective of this study is to investigate the ability of LES to predict turbulent combustion subject to system-level effects by considering a 360-degree annular combustor from the Energy Efficient Engine (EEE) program. In addition to showcasing LES calculations of the annular combustor, this study investigates the effects of incorporating a complex geometry on predicting self-sustaining oscillatory flows and its impact on combustion. To accomplish this, the massively parallel LES solver, CharLES, is employed, which utilizes a fully compressible Navier-Stokes Equation (NSE) solver and a flamelet progress variable approach on unstructured Voronoi-based cells. Due to the importance of estimating adequate grid size, the effect of mesh resolution is investigated by computing results on three grids and comparing results in terms of mean and fluctuating fields. A non-reacting analysis is first conducted to understand the unsteady fluid dynamics arising from the central recirculation zone, which plays an important role inflame stabilization. Next, the progress variable method is utilized to generate a combustion model coupled with Lagrangian particle tracking models for fuel spray breakup, vaporization, and ignition. The results, when compared to combustor exit temperature measurements from experiments, as well as previous LES simulations in the literature, show good agreement. Further analysis is conducted showing the onset of self-sustained oscillatory flow, owing to the azimuthal coupling, and proper orthogonal decomposition (POD) analysis shows the most energetic modes. Overall, the results are promising and present a novel tool for guiding the development of stable and reliable systems. This work is conducted in support of the DoD High Performance Computing Modernization Program (HPCMP) Frontier program at ARL and NAVAIR in collaboration with the University of Cincinnati, Cadence Design Systems, and Pratt & Whitney.