Investigation of the turbulent flame structure and topology at different Karlovitz numbers using the tangential stretching rate index

• Published in: Combustion and flame Vol. 200; pp. 155 - 167
• Main Authors: Manias, Dimitris M., Tingas, Efstathios-Al, Hernández Pérez, Francisco E., Malpica Galassi, Riccardo, Paolo Ciottoli, Pietro, Valorani, Mauro, Im, Hong G.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01-02-2019; Elsevier BV
• Subjects: Aerodynamics; Chemical reactions; Combustion; Complexity; Computational fluid dynamics; Computer simulation; CSP; Direct numerical simulation; Extreme combustion; Flame propagation; Flame structure; Flame topology; High Karlovitz number; Multiscale analysis; Organic chemistry; Premixed flames; Singular perturbation; Software; Stretching rate; Time; Topology; TSR; Turbulent flames; Turbulent flow; High Karlovitz number; Flame topology; CSP; Extreme combustion; TSR; Turbulent flames
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2018.11.023

Turbulent premixed flames at high Karlovitz numbers exhibit highly complex structures in different reactive scalar fields to the extent that the definition of the flame front in an unambiguous manner is not straightforward. This poses a significant challenge in characterizing the observable turbulent flame behaviour such as the flame surface density, turbulent burning velocity, and so on. Turbulent premixed flames are reactive flows involving physical and chemical processes interacting over a wide range of time scales. By recognizing the multi-scale nature of reactive flows, we analyze the topology and structure of two direct numerical simulation cases of turbulent H2/air premixed flames, in the thin reaction zone and distributed combustion regimes, using tools derived from the computational singular perturbation (CSP) method and augmented by the tangential stretching rate (TSR) analysis. CSP allows to identify the local time scale decomposition of the multi-scale problem in its slow and fast components, while TSR allows to identify the most energetic time scale during both the explosive and dissipative regime of the reactive flow dynamics together with the identification of the flame front in an unambiguous manner. Before facing the complexity of the turbulent flow regime, we carry out a preliminary analysis of a one-dimensional laminar premixed flame in view of highlighting similarities and differences between laminar and turbulent cases. Subsequently, it is shown that the TSR metric provides a reliable way to identify the turbulent flame topologies.