Unstrained and strained flamelets for LES of premixed combustion

Langella, Ivan; Swaminathan, Nedunchezhian

doi:10.1080/13647830.2016.1140230

Cited by 52 publications

(65 citation statements)

References 78 publications

(197 reference statements)

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“…The effect of strain on a premixed flamelet is well accepted to be important in the case of RANS simulations, however its relevance for LES is more controversial. Recent findings [20,21] show that, since part of the strain is resolved in the LES, its effect on the flame is implicitly captured as long as the local mesh size is appropriate. These preliminary findings have been confirmed by GT calculations [22][23][24] and show that strained flamelets are unnecessary at least for the conditions considered.…”

Section: Introductionmentioning

confidence: 99%

“…The Role of CFD in Modern Jet Engine Combustor Design DOI: http://dx.doi.org /10.5772/intechopen.88267 appropriate in several works (see for example [20,[32][33][34][35][36]). The beta function requires the first and second moments, thus the SGS joint PDF is expressed as…”

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confidence: 99%

“…Note that here the two PDFs are treated independently, which is usually acceptable in LES with an appropriate grid size [37]. The SGS variances obtained using their transport equations are better than using algebraic expressions since convective and diffusive processes are important at subgrid scales [20]. These equations are written as:…”

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confidence: 99%

“…(5) [27]. For the progress variable SGS variance, it is shown in [20] that the reactive term in this equation is of leading order at least for Δ of sizes comparable or larger than the flame thickness, and thus the SDR has to balance the sources coming from reaction and turbulence. Hence, the linear relaxation model is unsuitable on physical grounds.…”

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confidence: 99%

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The Role of CFD in Modern Jet Engine Combustor Design

Chen¹,

Langella²,

Swaminathan³

2020

Environmental Impact of Aviation and Sustainable Solutions

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Recent advances in the application of computational fluid dynamics (CFD) for turbulent combustion with the relevance for gas turbine jet engines are discussed. Large eddy simulation (LES) has emerged as a powerful approach to handle the highly turbulent, unsteady and thermochemically non-linear flows in the practical combustors, and it is a matter of time for the industry to replace the conventional Reynolds averaged Navier-Stokes (RANS) approach by LES as the main CFD tool for combustor research and development. Since combustion is a subgrid scale phenomenon in LES, appropriate modelling is required to describe the SGS combustion effects on the resolved scales. Among the various available models, the flamelet approach is seen to be a promising candidate for practical application because of its computational efficiency, robustness and accuracy. A revised flamelet formulation, FlaRe, is introduced to outline the general LES methodology for combustion modelling and then used for a range of test cases to demonstrate its capabilities for both laboratory burners and practical engine combustors. The LES results generally compare well with the experimental measurements showing that the important physical processes are captured in the simulations.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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The Role of CFD in Modern Jet Engine Combustor Design

Chen¹,

Langella²,

Swaminathan³

2020

Environmental Impact of Aviation and Sustainable Solutions

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“…For the conditions tested in this study, deconvolution does not introduce a significant bias in the flamelet models' predictions, while a quantitatively good prediction of the progress variable rate is obtained for both flamelet models considered. method has both its merits and drawbacks, and an in-depth discussion on the subject can be found in the reviews [3]- [5].Flamelet methods in particular are popular since they are relatively straightforward to implement, and have been applied in a number of LES studies both for premixed and for non-premixed flames, with overall good results [6]- [16]. These studies include flows in complex geometries and for different flow configurations (freely-propagating, recirculating, etc.).…”

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Assessment of deconvolution-based flamelet methods for progress variable rate modeling

Nikolaou¹

2018

AAOAJ

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A novel approach for modeling the progress variable reaction rate in Large Eddy Simulations of turbulent and reacting flows is proposed. This is done in the context of two popular flamelet models which require the progress variable variance as input. The approach is based on using a recently proposed deconvolution method for modeling the variance. The deconvolution-modeled variance, is used as an input in the flamelet models for modeling the filtered progress variable rate. The assessment of the proposed approach is conducted a priori using direct numerical simulation data of turbulent premixed flames. For the conditions tested in this study, deconvolution does not introduce a significant bias in the flamelet models' predictions, while a quantitatively good prediction of the progress variable rate is obtained for both flamelet models considered. method has both its merits and drawbacks, and an in-depth discussion on the subject can be found in the reviews [3]- [5].Flamelet methods in particular are popular since they are relatively straightforward to implement, and have been applied in a number of LES studies both for premixed and for non-premixed flames, with overall good results [6]- [16]. These studies include flows in complex geometries and for different flow configurations (freely-propagating, recirculating, etc.). The filtered progress variablec which is a main LES solution variable, and it's variance σ 2 = c 2 −cc as obtained from a suitable model, are used as parameters in prebuilt tables for obtaining important information and for providing closures for un-closed terms in the governing equations. This includes species mean (filtered) mass fractions, mean (filtered) reaction rates etc. Such methods offer a simple, yet effective way of providing detailed chemistry information (a posteriori), while keeping the computational requirements to a minimum.A key unclosed term in the transport equation for the progress variable,c, is the filtered progress variable reaction rate,w c , where the overbar denotes a spatial filtering operation as defined in the context of LES. This is a dominant term, particularly in the reaction zone of the flame [17], and an accurate model is required for this term. Two popular flamelet methods for modelingw c , and which involve the progress variable variance, are the presumed-pdf approach and the Filtered Laminar Flame (FLF) approach [7,13]. In the presumed-pdf approach, the progress variablec and it's variance σ 2 , are used to parameterise the progress variable pdfp(ζ;c, σ 2 ), where ζ is the sample-space variable forc. This pdf is usually taken to be a β-function. A usually steady, 1D, laminar flame solution is used for integrating with the pdf thus obtaining a closure for the rate. In the FLF approach, a 1D laminar flame solution is pre-filtered, and a table is constructed which contains values of the filtered reaction rate (or other variables of interest). This is done for discrete filter-width values, and the table contains the filtered values of the variables at all spatial p...

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