A priori filtered chemical source term modeling for LES of high Karlovitz number premixed flames

Lapointe, Simon; Blanquart, Guillaume

doi:10.1016/j.combustflame.2016.11.015

Cited by 27 publications

(33 citation statements)

References 44 publications

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“…It has been observed in a recent study [14] that the unfiltered chemical source term has large local fluctuations and thus is difficult to model with tabulation methods, while the filtered source term is more readily modelled as long as the filter is large enough ( ≥ δ th ). This implies that a tabulated chemistry approach based on flamelets can still be useful in the high Karlovitz number regimes of combustion.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, it is suggested in [15] that tabulation can be improved by including effects of strain on the flamelet, an effect that is well understood for the RANS framework but not as well established for the LES framework [16,17]. In [14] it was also noted that unstrained flamelet modelling can work for low and high Karlovitz number (Ka δ < 0.1 or Ka δ > 100) while at intermediate Ka the strain, curvature and differential diffusion effects can be important.…”

Section: Introductionmentioning

confidence: 99%

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Filtered Reaction Rate Modelling in Moderate and High Karlovitz Number Flames: an a Priori Analysis

Nilsson

Doan

et al. 2019

Flow Turbulence Combust

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Direct numerical simulations (DNS) of statistically planar flames at moderate and high Karlovitz number (Ka) have been used to perform an a priori evaluation of a presumed-PDF model approach for filtered reaction rate in the framework of large eddy simulation (LES) for different LES filter sizes. The model is statistical and uses a presumed shape, based here on a beta-distribution, for the sub-grid probability density function (PDF) of a reaction progress variable. Flamelet tabulation is used for the unfiltered reaction rate. It is known that presumed PDF with flamelet tabulation may lead to over-prediction of the modelled reaction rate. This is assessed in a methodical way using DNS of varying complexity, including single-step chemistry and complex methane/air chemistry at equivalence ratio 0.6. It is shown that the error is strongly related to the filter size. A correction function is proposed in this work which can reduce the error on the reaction rate modelling at low turbulence intensities by up to 50%, and which is obtained by imposing that the consumption speed based on the modelled reaction rate matches the exact one in the flamelet limit. A second analysis is also conducted to assess the accuracy of the flamelet assumption itself. This analysis is conducted for a wide range of Ka, from 6 to 4100. It is found that at high Ka this assumption is weaker as expected, however results improve with larger filter sizes due to the reduction of the scatter produced by the fluctuations of the exact reaction rate.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Filtered Reaction Rate Modelling in Moderate and High Karlovitz Number Flames: an a Priori Analysis

Nilsson

Doan

et al. 2019

Flow Turbulence Combust

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“…The filtering operation has been examined previously for non-reacting LES (e.g. [24]), and for combustion LES [25] targetting tabulated chemistry based on presumed PDFs. Here, Direct Numerical Simulation (DNS) results from lean premixed methane-air flames will be used to examine the influence of the underlying turbulent flow on the filtered reaction rates, and hence the modelling requirements for finite-rate chemistry LES.…”

Section: Introductionmentioning

confidence: 99%

An a priori analysis of a DNS database of turbulent lean premixed methane flames for LES with finite-rate chemistry

Aspden

Zettervall

Fureby

2019

Proceedings of the Combustion Institute

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An a priori analysis of a DNS database of turbulent lean premixed methane flames is presented considering the relative effects of turbulence and LES filtering, along with a potential modelling approach for LES with finite-rate chemistry. The leading-order effect was found to be due to the filter operation; flame response to turbulence was a secondary effect, and manifested primarily as an increase in standard deviations about conditional means. It was found that the radicals O, H and OH were less impacted by the filter than other high-temperature radicals, which were significantly reduced in magnitude by the filter. By considering reaction path diagrams, key reactions have been identified that are responsible for disparities between the desired filtered reaction rates and the reaction rates evaluated using quantities available in LES calculations (i.e. the filtered species and temperature). More specifically, the hydrogen abstraction reactions that take CH 4 to CH 3 (by O, H and OH) were found to have particularly enhanced reaction rates, and dominate the reaction path. Under the conditions presented, reaction paths were found to be independent of turbulence intensity. In general, the filtered reaction rates from the DNS were found to align more closely with the filtered laminar profile than the reaction rate of filtered species and temperature, (but disparities were found to decrease with increasing Karlovitz number). A simple model for scaling reaction rates is considered based on filtered laminar flame profiles, and the resulting reaction paths demonstrate proof-of-concept of a simple approach for formulating a reaction rate model for LES with finite-rate chemistry.

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“…Moreover, exact LES-like quantities which were directly filtered from DNS are used as model inputs. While a priori analyses have been used in many previous studies (see e.g., [17][18][19][20][21][22][23]), the outcomes should not be overrated. One of the drawbacks of a priori analyses is that the error which is produced and propagated in dynamical systems can not be observed.…”

Section: Introductionmentioning

confidence: 99%

An a priori DNS analysis of scale similarity based combustion models for LES of non-premixed jet flames

Shamooni

Cuoci

Faravelli

et al. 2019

Flow Turbulence Combust

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In this work, recently developed finite-rate dynamic scale similarity (SS) sub-grid scale (SGS) combustion models have been a priori assessed and compared with the Eddy Dissipation Concept (EDC) and "no model" approaches based on a Direct Numerical Simulation (DNS) database of a temporally evolving non-premixed jet flame. Two different filter widths, one placed in the inertial range and the other in the near dissipation range, have been used. The analyses were carried out in two time instants corresponding to instants of maximum local extinction and re-ignition. Conditional averaged filtered chemical source terms, conditioned on different parameters in the composition space, have been presented. Improvements are observed using the dynamic SS models compared to the two other approaches in the prediction of filtered chemical source terms of individual species while using larger filter widths. However, discrepancies still exists using the dynamic SS model on the turbulent/non-turbulent interfaces of the jet, mainly in the prediction of the oxidizer consumption rate.

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A priori filtered chemical source term modeling for LES of high Karlovitz number premixed flames

Cited by 27 publications

References 44 publications

Filtered Reaction Rate Modelling in Moderate and High Karlovitz Number Flames: an a Priori Analysis

Filtered Reaction Rate Modelling in Moderate and High Karlovitz Number Flames: an a Priori Analysis

An a priori analysis of a DNS database of turbulent lean premixed methane flames for LES with finite-rate chemistry

An a priori DNS analysis of scale similarity based combustion models for LES of non-premixed jet flames

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