Influence of flow structures and combustion on cross-scale turbulent kinetic energy transfer in premixed swirl flames.

Kazbekov, Askar; Steinberg, Adam M.

doi:10.1016/j.proci.2022.07.074

Cited by 5 publications

(3 citation statements)

References 18 publications

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“…2017; Kim et al. 2018; Ranjan & Menon 2018; Ahmed, Chakraborty & Klein 2019; Kazbekov & Steinberg 2021, 2023; MacArt & Mueller 2021; Datta, Mathew & Hemchandra 2022; Qian et al. 2022).…”

Section: Introductionmentioning

confidence: 99%

Backscatter of scalar variance in turbulent premixed flames

et al. 2023

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To explore the direction of inter-scale transfer of scalar variance between subgrid scale (SGS) and resolved scalar fields, direct numerical simulation data obtained earlier from two complex-chemistry lean hydrogen–air flames are analysed by applying Helmholtz–Hodge decomposition (HHD) to the simulated velocity fields. Computed results show backscatter of scalar (combustion progress variable $c$ ) variance, i.e. its transfer from SGS to resolved scales, even in a highly turbulent flame characterized by a unity-order Damköhler number and a ratio of Kolmogorov length scale to thermal laminar flame thickness as low as 0.05. Analysis of scalar fluxes associated with the solenoidal and potential velocity fields yielded by HHD shows that the documented backscatter stems primarily from the potential velocity perturbations generated due to dilatation in instantaneous local flames, with the backscatter being substantially promoted by a close alignment of the spatial gradient of mean scalar progress variable and the potential-velocity contribution to the local SGS scalar flux. The alignment is associated with the fact that combustion-induced thermal expansion increases local velocity in the direction of $\boldsymbol {\nabla } c$ . These results call for development of SGS models capable of predicting backscatter of scalar variance in turbulent flames in large eddy simulations.

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“…2017; Kim et al. 2018; Ranjan & Menon 2018; Ahmed, Chakraborty & Klein 2019; Kazbekov & Steinberg 2021, 2023; MacArt & Mueller 2021; Datta, Mathew & Hemchandra 2022; Qian et al. 2022).…”

Section: Introductionmentioning

confidence: 99%

Backscatter of scalar variance in turbulent premixed flames

et al. 2023

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“…Sirui Wang et al [ 13 ] revealed that the flame-induced flow acceleration near the burner outlet enhanced the vorticity and velocity in a stratified swirling flame, while the length of the recirculation zone was found to be smaller than that without reaction. The increasing back-scatter turbulent kinetic energy transfer was observed internal to the swirling flames instead of down-scale transfer in the non-reacting regions [ 14 ]. The experiment measured that the enstrophy production was determined by combustion and turbulence properties and the flame-induced baroclinic turbulence production should be considered [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

Entropy: An Inspiring Tool for Characterizing Turbulence–Combustion Interaction in Swirling Flames via Direct Numerical Simulations of Non-Premixed and Premixed Flames

Su,

Liu,

Xiao

et al. 2023

Entropy

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This article focuses on entropy generation in the combustion field, which serves as a useful indicator to quantify the interaction between turbulence and combustion. The study is performed on the direct numerical simulations (DNS) of high pressure non-premixed and premixed swirling flames. By analyzing the entropy generation in thermal transport, mass transport, and chemical reactions, it is found that the thermal transport, driven by the temperature gradient, plays a dominant role. The enstrophy transport analysis reveals that the responses of individual terms to combustion can be measured by the entropy: the vortex stretching and the dissipation terms increase monotonically with the increasing entropy. In high entropy regions, the turbulence behaves as the “cigar shaped” state in the non-premixed flame, while as the axisymmetric state in the premixed flame. A substantial increase in the normal Reynolds stress with the entropy is observed. This is due to the competition between two terms promoted by the entropy, i.e., the velocity–pressure gradient correlation term and the shear production term. As a result, the velocity–pressure gradient correlation tends to isotropize turbulence by transferring energy increasingly from the largest streamwise component to the other smaller normal components of Reynolds stress and is dominated by the fluctuating pressure gradient that increases along the entropy. The shear production term increases with the entropy due to the upgrading alignment of the eigenvectors of strain rate and Reynolds stress tensors.

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“…Accordingly, over the past decade, the phenomenon of combustion-induced backscatter was explored by several research groups by analyzing both numerical data obtained in Direct Numerical Simulation (DNS) studies of premixed turbulent flames stabilized in simple flow configurations [32][33][34][35][36][37][38][39][40][41][42] and experimental data obtained from swirl flames. 43,44 However, other important aspects of intermittency of inter-scale energy transfer were beyond the focus of the cited papers. For instance, the most common approaches to studying intermittency of inter-scale energy transfer 2,3,45 deal either with a Probability Density Function (PDF) of a quantity relevant to the transfer or with images of iso-surfaces of sub-filter scale (SFS) flux.…”

Section: Introductionmentioning

confidence: 99%