GALCIT Colloquium

Most systems used in transportation and energy conversion devices are powered through combustion of fuel in turbulent flows. The chemical activity is typically concentrated within thin flames, which are embedded in an otherwise non-reacting turbulent flow field. It is common to approximate the reaction zones by nominally one-dimensional (but highly curved) flamelets. Unfortunately, this description is unable to account naturally for multi-dimensional extinction/reignition phenomena appearing in turbulent combustion at high strains. Now, edge flames are two-dimensional structures consisting of curved edges that can arise at the boundary of a partially extinguished flame. In nonpremixed flames, edge flames consist of premixed segments (lean and/or rich in fuel), with a trailing diffusion flame that consumes the excess reactants behind the edge flame head. Edge flames are relevant in turbulent flows where finite-rate chemical processes lead to extinction/reignition of combustion; for example, near holes poked in turbulent diffusion flames at high strains (regions of strong turbulence activity) or at the stabilization region of a lifted jet flame. The objective of the talk is to discuss a structural flame model for turbulent combustion that couples consistently real gas chemistry, flame structure, and hydrodynamics using edge flames. We will discuss the mathematical formalism that necessitates the solution of an evolving field defined on a highly deformed moving surface and the computational strategy to tackle this equation. Furthermore, the talk will discuss an extension of these flame-abstraction ideas to large-eddy simulation (LES). The main application of this research is to high-speed propulsion and ultra-lean combustion.