The association of scalar dissipation rate layers and OH zones with strain, vorticity, and 2-D dilatation fields in turbulent nonpremixed jets and jet flames

In order to address the impact of the concentration gradients on the chemistry – turbulence interaction in turbulent flames, the REDIM reduced chemistry is constructed incorporating the scalar dissipation rate, which is a key quantity describing the turbulent mixing process. This is achieved by providing a variable gradient estimate in the REDIM evolution equation. In such case, the REDIM reduced chemistry is tabulated as a function of the reduced coordinates and the scalar dissipation rate as an additional progress variable. The constructed REDIM is based on a detailed transport model including the differential diffusion, and is validated for a piloted non-premixed turbulent jet flames (Sandia Flame D and E). The results show that the newly generated REDIM can reproduce the thermo-kinetic quantities very well, and the differential molecular diffusion effect can also be well captured.

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Correlation between small-scale velocity and scalar fluctuations in a turbulent channel flow

Journal of Fluid Mechanics ◽

10.1017/s0022112008005569 ◽

2009 ◽

Vol 627 ◽

pp. 1-32 ◽

Cited By ~ 49

Author(s):

HIROYUKI ABE ◽

ROBERT ANTHONY ANTONIA ◽

HIROSHI KAWAMURA

Keyword(s):

Strain Rate ◽

Channel Flow ◽

Dissipation Rate ◽

Compressive Strain ◽

Outer Region ◽

Turbulent Channel Flow ◽

Scalar Fields ◽

Scalar Dissipation ◽

Small Scale ◽

Scalar Dissipation Rate

Direct numerical simulations of a turbulent channel flow with passive scalar transport are used to examine the relationship between small-scale velocity and scalar fields. The Reynolds number based on the friction velocity and the channel half-width is equal to 180, 395 and 640, and the molecular Prandtl number is 0.71. The focus is on the interrelationship between the components of the vorticity vector and those of the scalar derivative vector. Near the wall, there is close similarity between different components of the two vectors due to the almost perfect correspondence between the momentum and thermal streaks. With increasing distance from the wall, the magnitudes of the correlations become smaller but remain non-negligible everywhere in the channel owing to the presence of internal shear and scalar layers in the inner region and the backs of the large-scale motions in the outer region. The topology of the scalar dissipation rate, which is important for small-scale scalar mixing, is shown to be associated with the organized structures. The most preferential orientation of the scalar dissipation rate is the direction of the mean strain rate near the wall and that of the fluctuating compressive strain rate in the outer region. The latter region has many characteristics in common with several turbulent flows; viz. the dominant structures are sheetlike in form and better correlated with the energy dissipation rate than the enstrophy.

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Modelling of Conditional Scalar Dissipation Rate in Turbulent Premixed Combustion

Computation ◽

10.3390/computation9030026 ◽

2021 ◽

Vol 9 (3) ◽

pp. 26 ◽

Cited By ~ 1

Author(s):

Shokri Amzin ◽

Mariusz Domagała

Keyword(s):

Dissipation Rate ◽

Premixed Flames ◽

Moment Closure ◽

Navier Stokes ◽

Scalar Dissipation ◽

Flame Surface ◽

Scalar Dissipation Rate ◽

Turbulent Premixed Flames ◽

Conditional Moment ◽

Turbulent Premixed

In turbulent premixed flames, for the mixing at a molecular level of reactants and products on the flame surface, it is crucial to sustain the combustion. This mixing phenomenon is featured by the scalar dissipation rate, which may be broadly defined as the rate of micro-mixing at small scales. This term, which appears in many turbulent combustion methods, includes the Conditional Moment Closure (CMC) and the Probability Density Function (PDF), requires an accurate model. In this study, a mathematical closure for the conditional mean scalar dissipation rate, <Nc|ζ>, in Reynolds, Averaged Navier–Stokes (RANS) context is proposed and tested against two different Direct Numerical Simulation (DNS) databases having different thermochemical and turbulence conditions. These databases consist of lean turbulent premixed V-flames of the CH4-air mixture and stoichiometric turbulent premixed flames of H2-air. The mathematical model has successfully predicted the peak and the typical profile of <Nc|ζ> with the sample space ζ and its prediction was consistent with an earlier study.

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