Impact of Volume Viscosity on the Structure of Turbulent Premixed Flames in the Thin Reaction Zone Regime

Fru, Gordon; Janiga, Gábor; Thévenin, Dominique

doi:10.1007/s10494-011-9360-1

Cited by 23 publications

(14 citation statements)

References 47 publications

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“…The bulk-viscosity coefficient, which accounts for the relaxation time needed to equilibrate translational and internal energies in the gas volume, is neglected in this study. However, under some conditions this coefficient can be, at least, of the same order of magnitude as the molecular viscosity (Cramer 2013), and its effects may become important in dilatational flows (Fru, Janiga & Thévenin 2012). In this work, these effects may be hindered since the fuel stream is highly diluted, and hydrogen is the species that exhibits the largest bulk-viscosity coefficient in the mixture.…”

Section: Formulationmentioning

confidence: 90%

Subgrid-scale backscatter in reacting and inert supersonic hydrogen–air turbulent mixing layers

et al. 2014

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This study addresses the dynamics of backscatter of kinetic energy in the context of large-eddy simulations (LES) of high-speed turbulent reacting flows. A priori analyses of direct numerical simulations (DNS) of reacting and inert supersonic, time-developing, hydrogen–air turbulent mixing layers with complex chemistry and multicomponent diffusion are conducted here in order to examine the effects of compressibility and combustion on subgrid-scale (SGS) backscatter of kinetic energy. The main characteristics of the aerothermochemical field in the mixing layer are outlined. A selfsimilar period is identified in which some of the turbulent quantities grow in a quasi-linear manner. A differential filter is applied to the DNS flow field to extract filtered quantities of relevance for the large-scale kinetic-energy budget. Spatiotemporal analyses of the flow-field statistics in the selfsimilar regime are performed, which reveal the presence of considerable amounts of SGS backscatter. The dilatation field becomes spatially intermittent as a result of the high-speed compressibility effect. In addition, the large-scale pressure-dilatation work is observed to be an essential mechanism for the local conversion of thermal and kinetic energies. A joint probability density function (PDF) of SGS dissipation and large-scale pressure-dilatation work is provided, which shows that backscatter occurs primarily in regions undergoing volumetric expansion; this implies the existence of an underlying physical mechanism that enhances the reverse energy cascade. Furthermore, effects of SGS backscatter on the Boussinesq eddy viscosity are studied, and a regime diagram demonstrating the relationship between the different energy-conversion modes and the sign of the eddy viscosity is provided along with a detailed budget of the volume fraction in each mode. A joint PDF of SGS dissipation and SGS dynamic-pressure dilatation work is calculated, which shows that high-speed compressibility effects lead to a decorrelation between SGS backscatter and negative eddy viscosities, which increases for increasingly large values of the SGS Mach number and filter width. Finally, it is found that the combustion dynamics have a marginal impact on the backscatter and flow-dilatation distributions, which are mainly dominated by the high-Mach-number effects.

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Section: Formulationmentioning

confidence: 90%

Subgrid-scale backscatter in reacting and inert supersonic hydrogen–air turbulent mixing layers

et al. 2014

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“…While monoatomic gases show no evidence of bulk viscosity effects, experimentally measured values of the bulk-to-shear viscosity ratio (κ/η) vary widely for most of the diatomic gases used nowadays in both academic and practical experimental and numerical combustion studies [12,14,15]. In [15], it is stated that the volume viscosity is at least of the same order of magnitude as the shear viscosity (η) at 300 K, with a ratio κ/η for hydrogen as high as 52 at a temperature of 1000 K. Our recent findings for turbulent premixed flames burning hydrogen-containing fuels show a nonnegligible influence of the volume viscosity term on the turbulent flame structure, even for average quantities [16]. On the other hand, first DNS computations for flames burning methane show a minor impact of volume viscosity for all considered cases for global flame properties such as the volume-integrated heat release rate and turbulent burning velocity [17].…”

Section: Introductionmentioning

confidence: 74%

“…The single input data subroutine EGSKm(), suitable for fine-grain-distributed architectures with large number of processors, has been used. The integer m attached to the subroutine name refers to the various methods/models used in evaluating κ [15,16]. It varies between 2 and 6.…”

Section: Direct Numerical Simulationmentioning

confidence: 99%

“…Further details concerning code structure, optimization, application, and recent upgraded/added modules can be found in [4,29]. In order to access higher values of Re t on fine-grain parallel systems, two turbulence generation techniques based on digital filters [30] and random noise diffusion [31] have been hybridized, implemented, and parallelized on massively parallel computers [16]. With this simple, flexible, and accurate approach, the restriction on problem size imposed by the previously implemented generator based on inverse FFT [32] has been alleviated, paving the way for simulations of large domains at considerably higher turbulent Reynolds numbers.…”

Section: Direct Numerical Simulationmentioning

confidence: 99%

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Direct Numerical Simulations of the Impact of High Turbulence Intensities and Volume Viscosity on Premixed Methane Flames

Fru

Janiga

Thévenin

2011

Journal of Combustion

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Parametric direct numerical simulations (DNS) of turbulent premixed flames burning methane in the thin reaction zone regime have been performed relying on complex physicochemical models and taking into account volume viscosity (κ). The combined effect of increasing turbulence intensities (u′) andκon the resulting flame structure is investigated. The turbulent flame structure is marred with numerous perforations and edge flame structures appearing within the burnt gas mixture at various locations, shapes and sizes. Stepping upu′from 3 to 12 m/s leads to an increase in the scaled integrated heat release rate from 2 to 16. This illustrates the interest of combustion in a highly turbulent medium in order to obtain high volumetric heat release rates in compact burners. Flame thickening is observed to be predominant at high turbulent Reynolds number. Via ensemble averaging, it is shown that both laminar and turbulent flame structures are not modified byκ. These findings are in opposition to previous observations for flames burning hydrogen, where significant modifications induced byκwere found for both the local and global properties of turbulent flames. Therefore, to save computational resources, we suggest that the volume viscosity transport term be ignored for turbulent combustion DNS at low Mach numbers when burning hydrocarbon fuels.

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“…The impact of bulk viscosity effects has been previously analyzed in several situations including shock-hydrogen bubble interactions [3], turbulent flames [8], compressible boundary layers [9], shock-boundary layer interaction [10], and planar shockwave [11]. All these studies confirm that the bulk viscosity effects may be significant.…”

Section: Introductionmentioning

confidence: 76%

On the role of bulk viscosity in compressible reactive shear layer developments

Boukharfane

Ferrer

Mura

et al. 2019

European Journal of Mechanics - B/Fluids

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a b s t r a c tDespite 150 years of research after the reference work of Stokes, it should be acknowledged that some confusion still remains in the literature regarding the importance of bulk viscosity effects in flows of both academic and practical interests. On the one hand, it can be readily shown that the neglection of bulk viscosity (i.e., κ = 0) is strictly exact for mono-atomic gases. The corresponding bulk viscosity effects are also unlikely to alter the flowfield dynamics provided that the ratio of the shear viscosity µ to the bulk viscosity κ remains sufficiently large. On the other hand, for polyatomic gases, the scattered available experimental and numerical data show that it is certainly not zero and actually often far from negligible. Therefore, since the ratio κ/µ can display significant variations and may reach very large values (it can exceed thirty for dihydrogen), it remains unclear to what extent the neglection of κ holds.The purpose of the present study is thus to analyze the mechanisms through which bulk viscosity and associated processes may alter a canonical turbulent flow. In this context, we perform direct numerical simulations (DNS) of spatially-developing compressible non-reactive and reactive hydrogen-air shear layers interacting with an oblique shock wave. The corresponding flowfield is of special interest for various reactive high-speed flow applications, e.g., scramjets. The corresponding computations either neglect the influence of bulk viscosity (κ = 0) or take it into consideration by evaluating its value using the EGlib library. The qualitative inspection of the results obtained for two-dimensional cases in either the presence or the absence of bulk viscosity effects shows that the local and instantaneous structure of the mixing layer may be deeply altered when taking bulk viscosity into account. This contrasts with some mean statistical quantities, e.g., the vorticity thickness growth rate, which do not exhibit any significant sensitivity to the bulk viscosity. Enstrophy, Reynolds stress components, and turbulent kinetic energy (TKE) budgets are then evaluated from three-dimensional reactive simulations. Slight modifications are put into evidence on the energy transfer and dissipation contributions. From the obtained results, one may expect that refined large-eddy simulations (LES) may be rather sensitive to the consideration of bulk viscosity, while Reynolds-averaged Navier-Stokes (RANS) simulations, which are based on statistical averages, are not. (A. Mura). structure of the fluid as well as the flowfield conditions. However, acoustic absorption measurements performed at room temperature have shown that the ratio of the volume to the shear viscosity κ/µ may be up to thirty for hydrogen at room temperature [2], and recent analyses of reactive multicomponent high-speed flows have confirmed that it is not justified to neglect it, except for the sake of simplicity [3]. The dilatational viscosity is important in describing sound attenuation in gaseous media, and the absorption o...

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Impact of Volume Viscosity on the Structure of Turbulent Premixed Flames in the Thin Reaction Zone Regime

Cited by 23 publications

References 47 publications

Subgrid-scale backscatter in reacting and inert supersonic hydrogen–air turbulent mixing layers

Subgrid-scale backscatter in reacting and inert supersonic hydrogen–air turbulent mixing layers

Direct Numerical Simulations of the Impact of High Turbulence Intensities and Volume Viscosity on Premixed Methane Flames

On the role of bulk viscosity in compressible reactive shear layer developments

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