Flame fingers and interactions of hydrodynamic and thermodiffusive instabilities in laminar lean hydrogen flames

Berger, Lukas; Grinberg, Michael; Jurgens, B.; Lapenna, Pasquale Eduardo; Creta, Francesco; Attili, Antonio; Pitsch, Heinz

doi:10.1016/j.proci.2022.07.010

Cited by 18 publications

(4 citation statements)

References 22 publications

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“…Dispersion relations ω(k) similar to the curve plotted in black crosses in Fig. 1(a) are well known from theoretical [58,59,60,61,62] and experimental [63,64] studies of DL instability, as well as from recent two-dimensional numerical simulations of thermo-diffusively unstable laminar flames [43,44,45,46,47,48]. As far as quasi-stationary values of ln(U L /S L ), reached at large t/τ f , see Fig.…”

Section: Dns Conditionssupporting

confidence: 73%

“…To the best of the authors' knowledge, this elegant idea has not yet been adapted in research into TD instability, probably, because neither measured nor theoretical (in the case of substantial density variations) dispersion relation ω T D (k) is known. However, recent two-dimensional numerical simulations of laminar premixed flames subject to TD instability [43,44,45,46,47,48] have partially bridged this knowledge gap by showing that ω T D (k) has a bell-shape form also, with…”

Section: A Key Pointmentioning

confidence: 99%

“…Here, Ka is a Karlovitz number; τ f = δ L /S L , S L , and δ L = (T b − T u )/ max{|dT /dx|} are the laminar flame time scale, speed, and thickness, respectively; T is the temperature; subscripts u and b designate unburned reactants and burned products; max{ω T D (k)} is the maximum growth rate of TD instability (dependence of the instability growth rate ω T D on the instability wavenumber k has a bell-like shape [43,44,45,46,47,48], as discussed in the next section); and τ K is Kolmogorov time scale, which characterizes the order of magnitude of the highest velocity gradients generated by the smallest-scale turbulent eddies [12,49,50]. Similar criteria of importance of DL instability in turbulent flows was earlier introduced using the same reasoning [19], as well as other reasoning [51,52], and results of subsequent numerical [53,54,55,56] and experimental [57] studies qualitatively supported those criteria by indicating a minor role played by DL instability under conditions of sufficiently intense turbulence.…”

Section: Introductionmentioning

confidence: 99%

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Turbulent burning velocity and thermo-diffusive instability of premixed flames

Lee¹,

Wu²,

Dai³

et al. 2023

Preprint

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Reported in the paper are results of unsteady three-dimensional direct numerical simulations of laminar and turbulent, lean hydrogen-air, complex-chemistry flames propagating in forced turbulence in a box. To explore the eventual influence of thermo-diffusive instability of laminar flames on turbulent burning velocity, (i) a critical length scale Λn that bounds regimes of unstable and stable laminar combustion is numerically determined by gradually decreasing the width Λ of computational domain until a stable laminar flame is obtained and (ii) simulations of turbulent flames are performed by varying the width from Λ < Λn (in this case, the instability is suppressed) to Λ > Λn (in this case, the instability may grow). Moreover, simulations are performed either using mixtureaveraged transport properties (low Lewis number flames) or setting diffusivities of all species equal to heat diffusivity of the mixture (equidiffusive flames), with all other things being equal. Obtained results show a significant increase in turbulent burning velocity UT when the boundary Λ = Λn is crossed in weak turbulence, but almost equal values of UT are computed at Λ < Λn and Λ > Λn in moderately turbulent flames characterized by Karlovitz number equal to 3.4 or larger. These results imply that thermo-diffusive instability of laminar premixed flames substantially affects burning velocity in weak turbulence only, in line with a simple criterion proposed by Chomiak and Lipatnikov (Phys. Rev. E 107, 015102, 2023).

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Section: Dns Conditionssupporting

confidence: 73%

Section: A Key Pointmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Turbulent burning velocity and thermo-diffusive instability of premixed flames

Lee¹,

Wu²,

Dai³

et al. 2023

Preprint

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“…Additional challenges arise when thermodiffusively unstable (i.e., lean hydrogen/air) flames are investigated, which feature a wide range of cellular structures and thin elongated fingers (Berger et al. 2019 , 2022 ; Day et al. 2009 ; Bell et al.…”

Section: Introductionmentioning

confidence: 99%

Hybrid algorithm for the detection of turbulent flame fronts

Chaib,

Zheng,

Hochgreb

et al. 2023

Exp Fluids

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This paper presents a hybrid and unsupervised approach to flame front detection for low signal-to-noise planar laser-induced fluorescence (PLIF) images. The algorithm combines segmentation and edge detection techniques to achieve low-cost and accurate flame front detection in the presence of noise and variability in the flame structure. The method first uses an adaptive contrast enhancement scheme to improve the quality of the image prior to segmentation. The general shape of the flame front is then highlighted using segmentation, while the edge detection method is used to refine the results and highlight the flame front more accurately. The performance of the algorithm is tested on a dataset of high-speed PLIF images and is shown to achieve high accuracy in finely wrinkled turbulent hydrogen-enriched flames with order of magnitude improvements in computation speed. This new algorithm has potential applications in the experimental study of turbulent flames subject to intense wrinkling and low signal-to-noise ratios. Graphic abstract

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