Direct numerical simulation of three-dimensional swirling n-heptane spray flames

Spray combustion is encountered in many engineering applications, such as internal combustion engines and gas-turbine aircraft engines. In these systems, the concurrent processes of liquid atomization, droplet evaporation, turbulent dispersion, and combustion interact and strongly affect each other, which makes experimental measurement and high-fidelity simulation challenging. To understand these multi-physics phenomena and their strong coupling interactions, methodology of direct numerical simulation (DNS) is helpful. DNS has been proven to be a powerful tool for exploring fundamentals of single-phase turbulent flows (Moin & Mahesh 1998) and turbulent combustion (Vervisch & Poinsot 1998). Recently, DNS has been applied to study spray combustion (Reveillon & Vervisch 2005; Domingo et al. 2005; Watanabe et al. 2008). Peraa & Reveillon (2007) further applied a two-dimensional compressible solver to explore the spray flame/acoustic interactions. However, all these studies are limited to two-dimensional and simple configurations. Large eddy simulation (LES) has also been extended to study spray combustion of realistic applications (Moin & Apte 2006; Patela et al. 2007). Although consistent results with experimental data have been achieved, using models of gaseous combustion to describe spray flames leads to some modeling issues, as discussed by Baba & Kurose (2008). For example, this approach suggests that combustion can be accurately modeled independent of spray evaporation. However, the combustion process is intricately coupled with the spray evaporation, and combustion models should correctly reflect these interactions. The present study is motivated by the above background. To gain a better understanding of three-dimensional spray flame behavior, as well as evaporation-combustion interactions in a more realistic configuration, direct numerical simulations of n-heptane spray flames in a model swirling combustor have been conducted. The simulations are performed to approach realistic spray combustion as much as possible. Potential insights into swirling spray combustion are presented, and relevant modeling issues are discussed.