Abstract
ABSTRACTLarge-eddy simulation (LES) is applied to a fuel-lean turbulent propane-air Bunsen flame in the corrugated-flamelet regime. The subgrid-scale (SGS) modeling includes a previously developed treatment of the total enthalpy along with three different SGS velocity, , models. In addressing the filtered reaction rate, a presumed probability density function (PDF) approach is employed for the reaction-progress variable, closed by a transport equation for its SGS variance. The statistics obtained using the three models are in good agreement with the measurements and do not differ significantly from each other for first-order moments suggesting that commonly used SGS modeling may be adequate to get the mean velocities and reaction progress variable. However, all three SGS velocity models fail to reflect a measured bimodality of the PDF of the radial component of the velocity in the central portion of the flame. This emphasizes a need for further development of models required at the reaction rate closure level for practical LES of combustion in the corrugated-flamelet regime.
Highlights
Lean premixed combustion is attractive for practical combustion devices because of its potential to deliver high efficiency and low emissions simultaneously
Flamelet approach can be further subdivided into geometrical and statistical approaches, with the G-equation and flame-surface-density-based methods belonging to the geometrical category and presumed probability density function (PDF) methods to the statistical category
The SGS velocity will be influenced by dilatation resulting from combustion, whence u0Δ values obtained from Eqs. (11) to (13) can differ, since these models presume the role of the dilatation differently
Summary
Lean premixed combustion is attractive for practical combustion devices because of its potential to deliver high efficiency and low emissions simultaneously. As a continuation of a series of experiments by Furukawa and co-workers (Furukawa et al, 2002; Furukawa and Williams, 2003; Furukawa et al, 2013a, 2013b), recently, Furukawa et al (2016) reported measured statistics of gas velocities, with reaction-progress-variable fields deduced therefrom in a non-piloted lean propane-air premixed Bunsen flame in an open environment This is one of four flames in the corrugated-flamelet regime that they investigated, and they suggested that it would be of interest to pursue numerical modeling of the experimental results. The subgrid idissipation rate (SDR) is defined from the equation eεc 1⁄4 DðÑc Á ÑcÞ À DðÑec Á ÑecÞ and is closed using an algebraic model (Dunstan et al, 2013): eεc 1⁄4 F
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