Abstract
The method of moments with interpolative closure (MOMIC) for soot formation and growth provides a detailed modeling framework maintaining a good balance in generality, accuracy, robustness, and computational efficiency. This study presents several computational issues in the development and implementation of the MOMIC-based soot modeling for direct numerical simulations (DNS). The issues of concern include a wide dynamic range of numbers, choice of normalization, high effective Schmidt number of soot particles, and realizability of the soot particle size distribution function (PSDF). These problems are not unique to DNS, but they are often exacerbated by the high-order numerical schemes used in DNS. Four specific issues are discussed in this article: the treatment of soot diffusion, choice of interpolation scheme for MOMIC, an approach to deal with strongly oxidizing environments, and realizability of the PSDF. General, robust, and stable approaches are sought to address these issues, minimizing the use of ad hoc treatments such as clipping. The solutions proposed and demonstrated here are being applied to generate new physical insight into complex turbulence-chemistry-soot-radiation interactions in turbulent reacting flows using DNS. Copyright 2014 American Association for Aerosol Research
Highlights
Combustion-generated particulate formation arises from incomplete fuel oxidation and poses serious environmental and health concerns (Lahaye and Prado 1983; U.S EPA 2009; Bond et al 2013)
It is important to understand the fundamental dynamics of soot formation, the underlying physical and chemical processes, and their interactions with turbulence and radiation
The term “Direct numerical simulation (DNS)” in the context of turbulent combustion refers to a simulation where all relevant continuum gas-phase length and time scales are fully resolved, and the chemical processes are modeled with varying degrees of approximation
Summary
Combustion-generated particulate formation arises from incomplete fuel oxidation and poses serious environmental and health concerns (Lahaye and Prado 1983; U.S EPA 2009; Bond et al 2013). As a reasonable compromise between fidelity and computational efficiency, the method of moments (Dobbins and Mulholland 1984; Frenklach 1985; Frenklach and Harris 1987; McGraw 1997; Wright et al 2001; Frenklach 2002; Moody and Collins 2003; Lignell et al 2008; Mueller et al 2009a,b) describes the key soot variables and the size distribution information by solving for a subset of moments of the PSDF, which are transported along with the gas-phase species These high-fidelity soot models have been available for some time, their implementation in combustion DNS applications is still new. A discussion of the effects of a dissipative filter on solution stability and soot diffusion for the particular class of numerical schemes (time-explicit, highorder finite differences) used in the current simulations is provided there
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