Large-Eddy Simulation of Nonpremixed Flames by Explicit Filtering

Abstract

Large-eddy simulation (LES) provides improved predictions in applications which are controlled by dynamics of large-scale structures. Since flames are often anchored by recirculating flows or mixing layers, turbulent combustion is an application where the promise of LES is being realized. Following a brief introduction to LES, and its models for the turbulence, some combustion models are discussed. Two approaches are discussed in greater detail. First, the extension of an explicit filtering method, and second the filtered mass density function method (FMDF), which is analogous to the pdf methods for turbulent combustion. The performance of these methods was assessed by examining LES of flames developing from alternating fuel and oxidizer layers embedded in homogeneous, isotropic turbulent fields. Solutions with the explicit filtering method are not too different from reference DNS (direct numerical simulation), and improves with grid refinement. The FMDF solutions are noticeably better even on a coarse grid. Evolution of mean quantities, as well as pdfs follow those of the DNS very closely at all times, even though snapshots of the fields do not resemble each other.