Prediction of autoignition in a lifted methane/air flame using an unsteady flamelet/progress variable model

Large eddy simulation of a lifted ethylene flame using a dynamic nonequilibrium model for subfilter scalar variance and dissipation rate

“…In the LES computations described in this work, combustion is modeled using an unsteady flamelet/progress variable approach [29], accounting for di↵erential di↵usion e↵ects [30,31]. The flamelet solutions are calculated using the same 22 species ethylene mechanism employed in the DNS [28].…”

RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF

“…In the simple steady axisymmetric jet configuration considered, we can expect that our well calibrated RANS simulation can provide enough information in terms of scalar mixing (mean mixture fraction, variance and mean scalar dissipation rate) together with the presumed-PDF assumptions considered (β-PDF for mixture fraction and log-normal PDF for the stoichiometric scalar dissipation rate). In particular, we expect the assumption of a log-normal PDF for χ st to allow to obtain a modelling framework where intermittent ignition events are considered in a good way and where minor species can be as well predicted as compared to LES modelling like [4][5][6] where a δ-PDF is assumed for χ st , or compared to LES-CMC like [32,33]. The proposed combustion model for RANS modelling of simple steady flames could be extended in a straightforward way to LES modelling (with some possible modifications of the presumed-PDF assumptions).…”

“…In unsteady flamelet/progress variable (UFPV) models, the strong underlying assumption is to suppose that the structure of the turbulent flame considered can be described by igniting and extinguishing laminar diffusion flamelets [1][2][3], where the mixture fraction Z and its scalar dissipation rate χ are key parameters. This kind of approach has received attention lately [4][5][6][7][8][9][10][11][12][13][14][15], resolving the unsteady flamelet equations in Z-space with the assumption of fixed-in-time χ-profile from the analytic steady solution of laminar counterflow diffusion flames. This paper is a contribution to UFPV modelling with presumed PDF in a RANS framework.…”

Development of a novel flamelet-based model to include preferential diffusion effects in autoignition of CH4/H2 flames

“…This leads to a significantly larger manifold and higher computational costs. The main advantage of IML manifold over the existing methods with an extra dimension for scalar dissipation rate [22,35] is realized for the case of mixing layer in which scalar dissipation rate decreases during the initial burning stage. This situation is of interest in order to model lift-off height and stabilization mechanism of lifted flames such as those in JHC burners [10].…”

“…IML flamelets are basically similar to the commonly used one-dimensional Igniting Counter-Flow diffusion flamelets (ICF flamelets) with a notable distinction in the initial condition and inflow momentum. In ICF flamelets, it is a common practice [19][20][21][22] to generate an initial condition by assuming a steady-state molecular mixing field between the fuel and oxidizer stream with frozen chemistry (ω = 0) as it is shown in Fig. 1.…”