Large eddy simulation of spray combustion in a lean direct injection combustor using a novel subgrid-scale stress model

Abstract

Large eddy simulation (LES) is an important tool for studying turbulent spray combustion and developing next-generation combustion devices. In LES, the subgrid-scale (SGS) stress needs to be modeled with the closure models. Among various SGS stress models, the recently developed flame surface and k-equation-based gradient model (FKGM) has shown sound performance in predicting the SGS stress because it can consider the effect of combustion on turbulence, which is rarely considered in previous studies of SGS modeling. In this study, the LES of spray combustion in the NASA lean direct injection combustor is conducted to further validate the FKGM model and analyze the complex spray flame structure. The FKGM model achieves good agreement with the experimental measurements in terms of gas mean and fluctuating velocities, which indicates the model’s accuracy. Radial profiles of temperature, major combustion products as well as droplet diameters are also well reproduced in the current simulation. The inner recirculation zone, small outer recirculation zones, and three main flame zones are well captured. The flame index is introduced to identify different combustion regimes in the complex spray flame where both premixed and diffusion regimes coexist. Quantitative statistics related to the heat release rate show that the heat release intensity of the premixed flame regime is higher than that of the diffusion regime. Overall, the good agreement with the experimental measurements demonstrates the predictive capability of the FKGM model for SGS stress modeling in turbulent spray combustion.