A Two-step CFD Framework for Spray Combustion: Multiphase LES-based Droplet Prediction Coupled with Detailed Chemistry

Abstract

Modeling fuel atomization in modern aircraft combustors remains challenging because liquid-gas interface dynamics, ligament formation, and droplet breakup are highly nonlinear. This study presents a systematic numerical framework for primary atomization and reactive flow simulation in airblast injectors. The methodology combines volume-of-fluid (VOF) interface capturing, wall-film modeling, and a discrete phase model (DPM) to resolve liquid breakup and generate nozzle-specific injection files for subsequent reactive simulations using flamelet generated manifolds (FGM) with real-fuel chemistry. A HyChem-based mechanism with 129 species and 880 reactions was employed.

Validation was performed using the DLR Generic Single Sector Combustor, showing good agreement for both isothermal and reactive cases. Compared with conventional hollow-cone injections requiring empirical tuning, the VOF-LWF-DPM approach captures coherent wall-film and ligament dynamics prior to secondary breakup. Adaptive mesh refinement near the liquid-air interface improved spray dispersion and reduced droplet size, demonstrating the balance needed between fidelity and computational cost.

The same methodology was applied to Hanwha Aerospace's airblast nozzle, with comparable agreement in spray and single-sector combustion tests. Simulations revealed large coherent structures, including trapped vortices and a precessing vortex core, that enhanced turbulent mixing. The injection model from VOF-LWF-DPM simulation enabled reactive simulations showing differences in flame structure and NOx formation relative to conventional injection models. The overall temperature distributions remained comparable under high-enthalpy conditions. The benefit of realistic spray boundary conditions is expected to increase under low-power and lean blowout regimes.