Advances in fundamental understanding of turbulent combustion and the development of physics-based predictive tools for design and optimization of the next generation of combustion devices are strategic areas of research for the development of a secure, environmentally sound energy infrastructure. In recent years, due to the advent of high-performance computers and advanced numerical algorithms, direct numerical simulation (DNS) has emerged as a valuable computational research tool, in concert with experimentation and theory.
With full access to the spatially and temporally resolved fields, DNS uniquely provides fundamental insight into turbulent combustion and statistical information required to develop and validate predictive models used for the design and optimization of combustion devices.
The role of DNS in delivering new scientific insight into turbulent combustion is illustrated using results from a recent 3D turbulent premixed flame simulation, performed at the NCCS/ORNL. To understand the influence of turbulence on the flame structure, we performed the first 3D fully resolved DNS of a spatially-developing lean methane-air turbulent Bunsen flame in the thin reaction zones regime with reduced chemistry. The simulation was advanced long enough to reach statistical stationarity. A reduced chemical mechanism for lean premixed methane-air flames was derived, customized to the parameter space of the DNS, and with minimal temporal stiffness. The DNS results show thickening of the preheat zone due to the action of the turbulent eddies. Correlations of flame thickness with strain rate and curvature were obtained. Conditional mean reaction rates of several key species were compared with unstrained and strained laminar reaction rate profiles. The results indicate that while there is considerable thickening of the preheat layer, the turbulent eddies do not signicantly disrupt the reaction zone. This may be due to the attenuation of turbulence near the inner layer due to heat release. Several more 3D simulations at higher turbulence intensities are planned. Also, feature-based analysis techniques will be used to post-process the simulation data and to study flame surface interaction, merging and annihilation of flame area.