The cross-scale physical-space transfer of kinetic energy in turbulent premixed flames

O'Brien, Jeffrey; Towery, Colin A.Z.; Hamlington, Peter E.; Ihme, Matthias; Poludnenko, Alexei; Urzay, Javier

doi:10.1016/j.proci.2016.05.005

Cited by 62 publications

(38 citation statements)

References 13 publications

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“…The latter may include topology based approaches [60][61][62][63][64]71] or transported pdf methods [53,[86][87][88]. The current work also suggests that pressure -reaction rate terms should be accounted for in LES simulations of premixed turbulent flames as such interactions typically occur on the unresolved scales and can result in significant cross-scale energy transfer [3].…”

Section: Discussionmentioning

confidence: 93%

“…However, chemical reactions typically occur on the unresolved scales and correlations with pressure fluctuations can result in significant cross-scale (i.e. backscatter) energy transfer [3]. The current study investigates the modelling of related correlations using moment based methods that offer a partial resolution of the unsteady fluid motion [4].…”

Section: Introductionmentioning

confidence: 99%

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The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

Tian

Lindstedt

2017

Combustion Theory and Modelling

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Premixed turbulent flames feature strong interactions between chemical reactions and turbulence that affect scalar and turbulence statistics. The focus of the present work is on clarifying the impact of pressure dilatation/flamelet scrambling effects with a comprehensive second-moment closure used for evaluation purposes. Model extensions that take into account flamelet orientation and molecular diffusion are derived. Isothermal pressure transport is included with an additional variable density contribution derived for the flamelet regime of combustion. The full closure is assessed by comparisons with direct numerical simulations (DNS) of statistically "steady" fully developed premixed turbulent planar flames at different expansion ratios. Subsequently, the prediction of lean premixed turbulent methane-air flames featuring fractal grid generated turbulence in an opposed jet geometry is considered. The overall agreement shows that "dilatation" effects contribute to counter-gradient transport and can also increase the turbulent kinetic energy significantly. Levels of anisotropy are broadly consistent with the DNS data and key aspects of opposed jet flames are well predicted. However, it is also shown that complications arise due to interactions between the imposed pressure gradient and combustion and that redistribution is affected along with the scalar flux at the leading edge. The latter is strongly affected by the reaction rate closure and, potentially, by pressure transport. Overall, the derived models offer significant improvements and can readily be applied to the modelling of premixed turbulent flames at practical rates of heat release.

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Section: Discussionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

Tian

Lindstedt

2017

Combustion Theory and Modelling

View full text Add to dashboard Cite

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“…The formulation of the problem solved here is described elsewhere (Towery et al 2016;O'Brien et al 2017). In short, the numerical code is the finite-volume one described in Poludnenko & Oran (2010) and integrates the unsteady compressible chemically reacting Navier-Stokes conservation equations for mass, momentum, species and total energy for a mixture of perfect gases.…”

Section: Computational Set-upmentioning

confidence: 99%

“…In that limit, the turbulence intensity is small and the eddy turnover time is much larger than the flame-transit time. As a consequence, to first order, the problem admits a linearized solution that describes the rapid straining of eddies as they pass across the thin flame, with the nonlinear convective dynamics required for inter-scale energy transfer and combustion-induced backscatter becoming higher-order effects that are not essential to the interaction (O'Brien et al 2017). More recently, Fourier-based computational analyses of energy transfer in flames subjected to stronger turbulent intensities have also rendered useful information about the scales participating in energy fluxes, including backscatter (Kolla et al 2014;Towery et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…Conversely, the SFS-cumulative flux corresponds to the overall transfer of energy crossing a given scale cutoff at a given region of space, with all smaller scales embedded in that region being used for the computation of the transfer rate. In the results, the focus is on energy fluxes related to the convection and pressure-gradient mechanisms of momentum transport because of their relevance for subgrid-scale energetics in turbulent premixed flames (O'Brien et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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Spatially localized multi-scale energy transfer in turbulent premixed combustion

et al. 2018

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A three-dimensional wavelet multi-resolution analysis of direct numerical simulations of a turbulent premixed flame is performed in order to investigate the spatially localized spectral transfer of kinetic energy across scales in the vicinity of the flame front. A formulation is developed that addresses the compressible spectral dynamics of the kinetic energy in wavelet space. The wavelet basis enables the examination of local energy spectra, along with inter-scale and subfilter-scale (SFS) cumulative energy fluxes across a scale cutoff, all quantities being available either unconditioned or conditioned on the local instantaneous value of the progress variable across the flame brush. The results include the quantification of mean spectral values and associated spatial variabilities. The energy spectra undergo, in most locations in the flame brush, a precipitous drop that starts at scales of the same order as the characteristic flame scale and continues to smaller scales, even though the corresponding decrease of the mean spectra is much more gradual. The mean convective inter-scale flux indicates that convection increases the energy of small scales, although it does so in a non-conservative manner due to the high aspect ratio of the grid, which limits the maximum scale level that can be used in the wavelet transform, and to the non-periodic boundary conditions, which exchange energy through surface forces, as explicitly elucidated by the formulation. The mean pressure-gradient inter-scale flux extracts energy from intermediate scales of the same order as the characteristic flame scale, and injects energy in the smaller and larger scales. The local SFS-cumulative contribution of the convective and pressure-gradient mechanisms of energy transfer across a given cutoff scale imposed by a wavelet filter is analysed. The local SFS-cumulative energy flux is such that the subfilter scales upstream from the flame always receive energy on average. Conversely, within the flame brush, energy is drained on average from the subfilter scales by convective and pressure-gradient effects most intensely when the filter cutoff is larger than the characteristic flame scale.

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Direct Numerical Simulations for Combustion Science: Past, Present, and Future

2017

Energy, Environment, and Sustainability

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The cross-scale physical-space transfer of kinetic energy in turbulent premixed flames

Cited by 62 publications

References 13 publications

The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

Spatially localized multi-scale energy transfer in turbulent premixed combustion

Direct Numerical Simulations for Combustion Science: Past, Present, and Future

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