The explicit filtering method for large eddy simulations of a turbulent premixed flame

Datta, Anindya; Mathew, Joseph; Hemchandra, Santosh

doi:10.1016/j.combustflame.2021.111862

Cited by 8 publications

(10 citation statements)

References 34 publications

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“…In this work, the aeroacoustic source fields are computed using a fully compressible LES code, the EFLES solver, which uses explicit filtering instead of subgrid scale models for the unresolved scales (see Mathew et al 2003Mathew et al , 2006Datta et al 2022, for more details). A hybrid approach is used to predict the far-field spectra from the computed near-field sources via Lighthill's acoustic analogy (Lighthill 1952(Lighthill , 1954, as discussed in § 2.2.…”

Section: Large-eddy Simulationsmentioning

confidence: 99%

“…The time step, t (see also table 1), is chosen to satisfy (U j + c ∞ ) t/ x min = 0.5, where x min is the smallest grid spacing of the computational grid, which is sufficient to ensure formal numerical stability (e.g. Datta et al 2022). In the EFLES approach, which derives from the prior approximate deconvolution modelling (ADM) method (see e.g.…”

Section: Large-eddy Simulationsmentioning

confidence: 99%

“…For a long enough time series of the collected data, a superposition of such calculated SPOD modes would automatically include the high-frequency jittering effects and hence radiate the correct sound, even for subsonic jets. The other important aspect of our LES, also referred to as explicit filtering LES (EFLES), is the total absence of the subgrid scale (SGS) terms (Mathew et al 2003;Mathew, Foysi & Friedrich 2006;Datta, Mathew & Hemchandra 2022). The use of SGS models in the context of jet noise computations has been somewhat controversial (see Brès & Lele 2019, for a discussion), while there were earlier attempts to develop subgrid scale noise models to estimate sound from the missing (unresolved) scales using information from the resolved scales via an acoustic analogy-type approach (see Bodony & Lele 2019).…”

Section: Introductionmentioning

confidence: 99%

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Reduced-order models of aeroacoustic sources for sound radiated in twin subsonic jets

Muthichur,

Vempati,

Hemchandra

et al. 2023

J. Fluid Mech.

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We construct reduced-order models of aeroacoustic sources for single and twin subsonic jets ( $M_j=0.9$ , $Re=3600$ ), with the goal of accurately recovering the far-field sound over a wide band of frequencies $St=[0.07,1.0]$ and directivity angles $\phi = [30^{\circ },120^{\circ }]$ within a subdecibel level accuracy. These models are realized via combining spatio-temporally coherent spectral proper orthogonal decomposition (SPOD) modes extracted directly from Lighthill's stress tensor, itself calculated using large-eddy simulation (LES). We consider two sets of twin subsonic jets of diameter $D$ each, with spacings of $0.1D$ and $1D$ , where the jets merge upstream and downstream of breakdown, respectively. The closely spaced twin jet decays the slowest due to reduced turbulent stresses which are, however, more broadband due to early merging. Such jets show strong shielding in the plane of jets, especially at shallow directivity angles where sound levels may drop below that of the single jet. The farther spaced twin jets have dynamics more akin to the constituent single jet with turbulent fluctuations peaking here at $St=0.34$ , but showing very little shielding, with their overall sound pressure level (OASPL) mostly linked to the nature of extra flow structures created during merging. Three-dimensional, energy-ranked, coherent structures for twin jets exhibit rather poor low-rank behaviour, especially at the far-field spectral peak $St=0.14$ . At $St \gtrsim 0.3$ , the SPOD wavepackets show strong visual coherence, resembling Kelvin–Helmholtz instability modes upstream of breakdown, while at the lower frequencies, there is very little spatial coherence with wavepackets peaking downstream of breakdown. Although the leading SPOD modes radiate poorly, reduced-order models using a subset of them, up to $45$ SPOD modes per frequency, show a remarkable match (within $1$ dB) against the LES-predicted sound over $0.1 \lesssim St \lesssim 0.5$ , at all angles investigated. At other frequencies, the closely spaced twin jet shows more error, due to its greater hierarchy of spatio-temporal structures, showing slower convergence at the shallower angles.

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Section: Large-eddy Simulationsmentioning

confidence: 99%

Section: Large-eddy Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reduced-order models of aeroacoustic sources for sound radiated in twin subsonic jets

Muthichur,

Vempati,

Hemchandra

et al. 2023

J. Fluid Mech.

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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%

“…mean dilatation is positive, contrary to a typical non-reacting compressible flow, and is sufficiently large when compared with velocity gradients in the incoming turbulence), with injection of kinetic energy and mixture non-uniformities occurring at small scales and being well correlated (confined to the same zones). Accordingly, the phenomenon of backscatter of SGS kinetic energy in flames has received extensive attention over the past years (Kolla et al 2014;Ranjan et al 2016;Towery et al 2016;O'Brien et al 2017;Kim et al 2018 Datta, Mathew & Hemchandra 2022;Qian et al 2022). On the contrary, backscatter of SGS scalar variance in turbulent flames has rarely been explored (Ranjan et al 2016), in spite of the fact that, as noted in the next section, this phenomenon is closely linked with SGS counter-gradient scalar transport, which is often addressed in LES of premixed turbulent combustion (Boger et al 1998;Weller et al 1998;Tullis & Cant 2002;Richard et al 2007;Pfadler et al 2009;Lecocq et al 2010;Klein, Chakraborty & Gao 2016;Klein et al 2018).…”

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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Recent developments in DNS of turbulent combustion

Domingo

2023

Proceedings of the Combustion Institute

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The explicit filtering method for large eddy simulations of a turbulent premixed flame

Cited by 8 publications

References 34 publications

Reduced-order models of aeroacoustic sources for sound radiated in twin subsonic jets

Reduced-order models of aeroacoustic sources for sound radiated in twin subsonic jets

Backscatter of scalar variance in turbulent premixed flames

Recent developments in DNS of turbulent combustion

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