A priori investigation of PDF-modeling assumptions for a turbulent swirling bluff body flame (‘SM1’)

Meester, Reni De; Naud, Bertrand; Merci, Bart

doi:10.1016/j.combustflame.2012.06.018

Cited by 8 publications

(9 citation statements)

References 27 publications

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“…The comparisons between DNS and models are a priori comparisons, excluding therefore errors linked to numerics and other models. Several past studies have been devoted to the a priori validation of other turbulent combustion models using either DNS results [40] or experimental results [41,42]. In the present work, the comparison with DNS results has been retained as it excludes potential errors from the chemistry modelling from the comparisons.…”

Section: Dns Post-processing For Model Validationmentioning

confidence: 99%

Evaluation of different turbulent combustion models based on tabulated chemistry using DNS of heterogeneous mixtures

Chevillard

Michel

Pera

et al. 2016

Combustion Theory and Modelling

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This study used direct numerical simulations (DNSs) of combustion processes in turbulent heterogeneous mixtures for self-igniting partially-premixed configurations to assess the accuracy of partially-premixed turbulent combustion models that are based on the tabulation of chemistry progress in homogeneous reactors (HRs). DNS coupled with n-heptane/air detailed chemistry solving was considered as a reference result. Because the same detailed chemistry was used to generate the chemistry databases, the study was focused entirely on validating the modelling assumptions. Various HR-based tabulation models were tested: (1) the tabulated homogeneous reactor (THR) model, which is a direct exploitation of HR tabulation lacking any statistical information concerning mixture heterogeneity; (2) the presumed conditional moment (PCM) model, which includes a limited statistical description of the mixture and/or of the combustion advancement; (3) approximated diffusion flame (ADF) models, which consider the heterogeneous turbulent reactor as either a unique diffusion flame (simple ADF model formulation) or as a collection of flamelets with different strain rates (ADFχ model). A priori response of the above mentioned models was compared with detailed chemistry DNS results. The main findings are as follows: (1) A direct use of HR tabulation (THR model) led to overly inaccurate results; (2) an assumed independence between mixture fraction and progress variable was responsible for most PCM modelling failures in the context of turbulent heterogeneous self-ignited combustion; (3) the presumed beta-function of the progress variable distribution is likely to fail because of the complexity of auto-ignition kinetics; (4) the best results were obtained with the ADF models; (5) a simple ADF formulation is preferable to ADFχ, which showed limitations in terms of accuracy concerning the distribution of the progress variable ;(6) all tested models provided an acceptable prediction of the auto ignition delays but only ADF and ADFχ models are able to represent the temporal evolution of the progress variable.

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Section: Dns Post-processing For Model Validationmentioning

confidence: 99%

Evaluation of different turbulent combustion models based on tabulated chemistry using DNS of heterogeneous mixtures

Chevillard

Michel

Pera

et al. 2016

Combustion Theory and Modelling

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“…The first representation is not a good starting point for presumed-PDF modelling since Z, χ and Y c are all interdependent [49]. In order to obtain a tabulation in terms of Z, Z 2 , χ and Y c , we rather start from the second representation where we can reasonably assume statistical independence of the variables Z and a on the one hand, and Z and τ on the other hand.…”

Section: Joint Pdf Consideredmentioning

confidence: 99%

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

Naud

Novella

Pastor

et al. 2015

Combustion and Flame

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Elsevier Naud, B.; Novella Rosa, R.; Pastor Enguídanos, JM.; Winklinger, JF. (2015). RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF. Combustion and Flame. 162 (4) AbstractAn unsteady flamelet / progress variable (UFPV) approach is used to model a lifted H 2 /N 2 flame in a RANS framework together with presumed PDF. We solve the unsteady flamelets both in physical space and in mixture fraction space. We show that in the former case, the scalar dissipation rate profile strongly varies in time (while it is assumed to be fixed in time in the latter). However, this does not result in significant qualitative differences in the corresponding flamelet libraries. The progress variable is carefully defined, including both the main combustion product (H 2 O) and a key radical species in ignition process (HO 2 ). The presumed-PDF model is proposed in terms of the non-normalised progress variable, without assuming its statistical independence with mixture fraction. We introduce a modelled transport equation for the mean progress variable which is consistent with the basic underlying UFPV assumption, derived from the Lagrangian flamelet model. The influence of different model parameters on the results for the mean temperature and mean species mass fractions and their fluctuations is discussed. Good results are obtained for the conditions of the considered lifted flame where detailed experimental data is available. However, at low coflow temperature the modelled flame lift-off height is shorter than expected.

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“…Note that there appears to be local extinction at the location x=D B ¼ 0:6. This is in fact inert mixing in the outer shear layer, as pointed out by Liu et al and De Meester et al [26]: for the LES/HPDF calculation, all the data points in the low temperature band lie in the region r=R B > 0:94. The agreement of the LES/HPDF conditional means to those of the experiment is good, with the exception that the present simulation does not capture the sharp decrease in the conditional mean between the stoichiometric point and n ¼ 0:07.…”

Section: Resultsmentioning

confidence: 85%

Large eddy simulation/probability density function simulations of bluff body stabilized flames

Popov

Pope

2014

Combustion and Flame

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Keywords:Turbulent nonpremixed flame Bluff-body flow LES/PDF simulation Finite volume/Lagrangian particle algorithms for turbulent reactive flow simulation Local extinction a b s t r a c t This work presents large eddy simulation/probability density function (LES/PDF) simulation results for the Sandia/Sydney series of bluff-body stabilized CH 4 =H 2 flames. Results are presented for the flames HM1, HM2 and HM3, using the 19-species ARM2 reduced chemical mechanism, and comparison is made with previous numerical simulations of the same flames. When compared to previous numerical studies of these bluff-body flames, the present simulation shows considerable improvement, particularly in the downstream regions of the flow. The simulations are shown to be sensitive to the treatment of heat transfer to the bluff-body face, with better agreement in the temperature profiles achieved with the addition of a Dirichlet temperature boundary condition.

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A priori investigation of PDF-modeling assumptions for a turbulent swirling bluff body flame (‘SM1’)

Cited by 8 publications

References 27 publications

Evaluation of different turbulent combustion models based on tabulated chemistry using DNS of heterogeneous mixtures

Evaluation of different turbulent combustion models based on tabulated chemistry using DNS of heterogeneous mixtures

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

Large eddy simulation/probability density function simulations of bluff body stabilized flames

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