Direct numerical simulation of non-premixed turbulent flames

Non-premixed turbulent combustion processes control most practical applications of combustion. Studying these mechanisms has been the objective of numerous theoretical and experimental works in the last century. In the past 10 years, direct numerical simulation (DNS) has emerged as a new methodology. It has become an essential tool to understand and model turbulent combustion. DNS numerically solves the set of equations describing turbulent flames by resolving all chemical and flow scales. Because formulated assumptions can be tested accurately, the resulting data provide unique information to build turbulent combustion models. This review first discusses the fundamental properties of laminar diffusion flames. It then presents various DNS results to illustrate the different problems that can be studied using this tool. These problems include validity of the modeling hypothesis, topology of flame surfaces, and ignition and extinction mechanisms. The review also discusses the different analysis techniques employed to extract information from DNS and explores the limits of these methods.