An analysis of lower-dimensional approximations to the scalar dissipation rate using direct numerical simulations of plane 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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Numerical and Theoretical Analysis of Laminar Counterflowing Spray Flames for Use in Turbulent Combustion Modeling

Volume 1C, Symposia: Fundamental Issues and Perspectives in Fluid Mechanics; Industrial and Environmental Applications of Fluid Mechanics; Issues and Perspectives in Automotive Flows; Gas-Solid Flows: Dedicated to the Memory of Professor Clayton T. Crowe; Numerical Methods for Multiphase Flow; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes ◽

10.1115/fedsm2014-21994 ◽

2014 ◽

Author(s):

Hernan Olguin ◽

Philip Hindenberg ◽

Eva Gutheil

Keyword(s):

Numerical Simulations ◽

Dissipation Rate ◽

Numerical Study ◽

Mixture Fraction ◽

Flame Structure ◽

Main Reaction ◽

Computational Time ◽

Scalar Dissipation ◽

Scalar Dissipation Rate ◽

Spray Flames

The paper presents a combined theoretical and numerical study of laminar counterflow mono-disperse spray flames. The numerical model includes a similarity transformation of the two-dimensional governing gas phase equations into a one-dimensional formulation. The reduced computational time enables the use of detailed chemical reaction mechanisms to study the spray flame structure. In particular, the effect of spray evaporation on combustion is investigated by means of numerical simulations. For this purpose, the transport equation of the scalar dissipation rate of the mixture fraction is derived, where the spray evaporation source term is included. Numerical simulations of laminar liquid and gaseous ethanol and combustion products mono disperse spray flames under fuel-rich conditions are presented and discussed. The parametric dependence of the flame structures on strain rate is studied with emphasis on the spray evaporation. Droplet reversal and oscillation are found to dominate the flame structure, and they determine the location of the main reaction zone as well as the profile of the scalar dissipation rate. The study aims to develop a novel spray flamelet model for use in the numerical simulations of turbulent spray combustion with particular emphasis on flameless conditions.

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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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