Velocity and Reactive Scalar Dissipation Spectra in Turbulent Premixed Flames

Kolla, Hemanth; Zhao, Xinyu; Chen, Jacqueline H.; Swaminathan, Nedunchezhian

doi:10.1080/00102202.2016.1197211

Cited by 22 publications

(9 citation statements)

References 26 publications

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“…It has recently been reported that the heat release due to combustion modifies the spectra of turbulent kinetic energy (Kolla et al 2014) and its dissipation rate (Kolla et al 2016) in turbulent premixed flames in comparison to the corresponding results obtained for turbulent non-reacting flows. The two-point velocity correlations for the velocity field in turbulent premixed flames need to account for density differences between two points in question due to thermal expansion effects.…”

Section: Introductionmentioning

confidence: 92%

“…The two-point velocity correlations for the velocity field in turbulent premixed flames need to account for density differences between two points in question due to thermal expansion effects. This type of spectral analysis has the potential to provide insights into the scales where the correlation between pressure and dilatation remains important, which, in turn, affect the spectral energy transfer from lower to higher wavenumbers (Kolla et al 2014(Kolla et al , 2016. The predominantly positive dilatation rate due to thermal expansion in premixed turbulent flames also influences turbulent kinetic energy transport through the correlation between pressure and dilatation rate (Zhang and Rutland 1995;Nishiki et al 2002;Chakraborty and Cant 2009c;Chakraborty et al 2011a).…”

Section: Introductionmentioning

confidence: 99%

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Influence of Thermal Expansion on Fluid Dynamics of Turbulent Premixed Combustion and Its Modelling Implications

Chakraborty

2021

Flow Turbulence Combust

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The purpose of this paper is to demonstrate the effects of thermal expansion, as a result of heat release arising from exothermic chemical reactions, on the underlying turbulent fluid dynamics and its modelling in the case of turbulent premixed combustion. The thermal expansion due to heat release gives rise to predominantly positive values of dilatation rate within turbulent premixed flames, which has been shown to have significant implications on the flow topology distributions, and turbulent kinetic energy and enstrophy evolutions. It has been demonstrated that the magnitude of predominantly positive dilatation rate provides the measure of the strength of thermal expansion. The influence of thermal expansion on fluid turbulence has been shown to strengthen with decreasing values of Karlovitz number and characteristic Lewis number, and with increasing density ratio between unburned and burned gases. This is reflected in the weakening of the contributions of flow topologies, which are obtained only for positive values of dilatation rate, with increasing Karlovitz number. The thermal expansion within premixed turbulent flames not only induces mostly positive dilatation rate but also induces a flame-induced pressure gradient due to flame normal acceleration. The correlation between the pressure and dilatation fluctuations, and the vector product between density and pressure gradients significantly affect the evolutions of turbulent kinetic energy and enstrophy within turbulent premixed flames through pressure-dilatation and baroclinic torque terms, respectively. The relative contributions of pressure-dilatation and baroclinic torque in comparison to the magnitudes of the other terms in the turbulent kinetic energy and enstrophy transport equations, respectively strengthen with decreasing values of Karlovitz and characteristic Lewis numbers. This leads to significant augmentations of turbulent kinetic energy and enstrophy within the flame brush for small values of Karlovitz and characteristic Lewis numbers, but both turbulent kinetic energy and enstrophy decay from the unburned to the burned gas side of the flame brush for large values of Karlovitz and characteristic Lewis numbers. The heat release within premixed flames also induces significant anisotropy of sub-grid stresses and affects their alignments with resolved strain rates. This anisotropy plays a key role in the modelling of sub-grid stresses and the explicit closure of the isotropic part of the sub-grid stress has been demonstrated to improve the performance of sub-grid stress and turbulent kinetic energy closures. Moreover, the usual dynamic modelling techniques, which are used for non-reacting turbulent flows, have been shown to not be suitable for turbulent premixed flames. Furthermore, the velocity increase across the flame due to flame normal acceleration may induce counter-gradient transport for turbulent kinetic energy, reactive scalars, scalar gradients and scalar variances in premixed turbulent flames under some conditions. The propensity of counter-gradient transport increases with decreasing values of root-mean-square turbulent velocity and characteristic Lewis number. It has been found that vorticity aligns predominantly with the intermediate principal strain rate eigendirection but the relative extents of alignment of vorticity with the most extensive and the most compressive principal strain rate eigendirections change in response to the strength of thermal expansion. It has been found that dilatation rate almost equates to the most extensive strain rate for small sub-unity Lewis numbers and for the combination of large Damköhler and small Karlovitz numbers, and under these conditions vorticity shows no alignment with the most extensive principal strain rate eigendirection but an increased collinear alignment with the most compressive principal strain rate eigendirection is obtained. By contrast, for the combination of high Karlovitz number and low Damköhler number in the flames with Lewis number close to unity, vorticity shows an increased collinear alignment with the most extensive principal direction in the reaction zone where the effects of heat release are strong. The strengthening of flame normal acceleration in comparison to turbulent straining with increasing values of density ratio, Damköhler number and decreasing Lewis number makes the reactive scalar gradient align preferentially with the most extensive principal strain rate eigendirection, which is in contrast to preferential collinear alignment of the passive scalar gradient with the most compressive principal strain rate eigendirection. For high Karlovitz number, the reactive scalar gradient alignment starts to resemble the behaviour observed in the case of passive scalar mixing. The influence of thermal expansion on the alignment characteristics of vorticity and reactive scalar gradient with local principal strain rate eigendirections dictates the statistics of vortex-stretching term in the enstrophy transport equation and normal strain rate contributions in the scalar dissipation rate and flame surface density transport equations, respectively. Based on the aforementioned fundamental physical information regarding the thermal expansion effects on fluid turbulence in premixed combustion, it has been argued that turbulence and combustion modelling are closely interlinked in turbulent premixed combustion. Therefore, it might be necessary to alter and adapt both turbulence and combustion modelling strategies while moving from one combustion regime to the other.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Influence of Thermal Expansion on Fluid Dynamics of Turbulent Premixed Combustion and Its Modelling Implications

Chakraborty

2021

Flow Turbulence Combust

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“…The SP dataset is from the simulation of a three-dimensional statistically steady planar turbulent premixed flame of methane-air combustion. The simulation considers reduced chemical kinetics of 6 species, which results in a total of 11 simulation variables [14]. Unlike the HCCI and TJLR datasets, the SP dataset represents a statistically steady, rather than a temporally evolving, turbulent flame.…”

Section: A Data Descriptionmentioning

confidence: 99%

Parallel Tensor Compression for Large-Scale Scientific Data

Austin

Ballard

Kolda

2016

2016 IEEE International Parallel and Distributed Processing Symposium (IPDPS)

121

162

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Abstract-As parallel computing trends towards the exascale, scientific data produced by high-fidelity simulations are growing increasingly massive. For instance, a simulation on a three-dimensional spatial grid with 512 points per dimension that tracks 64 variables per grid point for 128 time steps yields 8 TB of data, assuming double precision. By viewing the data as a dense five-way tensor, we can compute a Tucker decomposition to find inherent low-dimensional multilinear structure, achieving compression ratios of up to 5000 on realworld data sets with negligible loss in accuracy. So that we can operate on such massive data, we present the first-ever distributed-memory parallel implementation for the Tucker decomposition, whose key computations correspond to parallel linear algebra operations, albeit with nonstandard data layouts. Our approach specifies a data distribution for tensors that avoids any tensor data redistribution, either locally or in parallel. We provide accompanying analysis of the computation and communication costs of the algorithms. To demonstrate the compression and accuracy of the method, we apply our approach to real-world data sets from combustion science simulations. We also provide detailed performance results, including parallel performance in both weak and strong scaling experiments.

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“…Also, velocity and scalar dissipation spectra deduced using DNS data of premixed flames lend support for this view. 43 . Hence, we shall use Eq.…”

Section: Scalar and Its Dissipation Spectramentioning

confidence: 99%

Scalar fluctuation and its dissipation in turbulent reacting flows

Swaminathan

Chakraborty

2021

Physics of Fluids

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The dissipation rate of a scalar variance is related to mean heat release rate in turbulent combustion. Mixture fraction is the scalar of interest for non-premixed combustion and a reaction progress variable is relevant for premixed combustion. A great deal of work is conducted in past studies to understand the spectra of passive scalar transport in turbulent flows. A very brief summary of these studies to bring out salient characteristics of passive scalar spectrum is given first. Then, the classical analysis of reactive scalar spectrum is revisited in the lights of recent understanding gained through analyzing the scalar spectrum deduced from direct numerical simulation data of both non-premixed and premixed combustion. The analysis shows that the reactive scalar spectral density in premixed combustion has a dependence on Karlovitz and Damköhler numbers, which comes through the mean scalar dissipation rate appearing in the spectral expression. In premixed combustion, the relevant scale for the scalar dissipation rate is shown to be of the order of the chemical length scale and the dissipation rate is not influenced by the scales in the inertial-convective range unlike for the passive scalar dissipation rate. The scalar fluctuations produced near the chemical scales cascade exponentially to larger scales. These observations imply that the passive scalar models cannot be extended to premixed combustion.

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Velocity and Reactive Scalar Dissipation Spectra in Turbulent Premixed Flames

Cited by 22 publications

References 26 publications

Influence of Thermal Expansion on Fluid Dynamics of Turbulent Premixed Combustion and Its Modelling Implications

Influence of Thermal Expansion on Fluid Dynamics of Turbulent Premixed Combustion and Its Modelling Implications

Parallel Tensor Compression for Large-Scale Scientific Data

Scalar fluctuation and its dissipation in turbulent reacting flows

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