A General Semicausal Stochastic Model for Turbulence/Radiation Interactions in Flames

1997 ◽  
Vol 119 (3) ◽  
pp. 509-516 ◽  
Author(s):  
S. H. Chan ◽  
X. C. Pan
Keyword(s):  
Causal Model ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Reynolds Numbers ◽  
Time Space ◽  
Proposed Model ◽  
Geometric Space ◽  
Mean And Variance ◽  
Air Diffusion ◽  
Spectral Intensities

This paper presents a general two-dimensional non-stationary semicausal model for the simulation of mixture fraction, which improves our previous causal model. The proposed model includes not only the pre-correlation predictors (both in time space and geometric space) as well as the cross-correlation predictors, as in the causal model, but also post-correlation predictors. The latter makes possible the consideration of interactions of a scalar, such as mixture fraction, at a physical location with that of all its adjacent locations. It has also been shown that the complicated second-and higher-order correlation predictors can be neglected in the semicausal simulation of mixture fraction. To show the validity of the model, the stochastic mean and variance of the spectral intensities at different wavelengths were predicted and compared with detailed experimental data for turbulent carbon monoxide/hydrogen/air diffusion flames having different Reynolds numbers. These comparisons showed excellent agreement with existing data and the improvement over the prior causal model.

scholarly journals Structure and Radiation Properties of Luminous Turbulent Acetylene/Air Diffusion Flames

1988 ◽  
Vol 110 (1) ◽  
pp. 173-181 ◽  
Author(s):  
J. P. Gore ◽  
G. M. Faeth
Keyword(s):  
Radiative Heat ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Heat Fluxes ◽  
Band Model ◽  
Spectral Radiation ◽  
Radiative Heat Loss ◽  
Radiation Properties ◽  
Air Diffusion ◽  
Laminar Flamelet

An experimental and theoretical study of the structure and radiation properties of luminous, round, turbulent acetylene/air diffusion flames is described. Measurements were made of mean and fluctuating velocities, mean concentrations, laser extinction (514 and 632.8 nm), spectral radiation intensities (1200–5500 nm), and radiative heat fluxes. The measurements were used to evaluate structure predictions based on the laminar flamelet concept, and radiation predictions based on a narrow-band model both ignoring and considering turbulence/radiation interactions. State relationships needed for the laminar flamelet concept were found from auxiliary measurements in laminar flames. Predictions were encouraging; however, quantitative accuracy was inferior to earlier findings for luminous flames. This is attributed to the large radiative heat loss fractions of acetylene/air flames (approaching 60 percent of the heat release rate); coupled structure and radiation analysis should be considered for improved results. The findings suggest significant turbulence/radiation interactions (increasing spectral intensities 40–100 percent from estimates based on mean properties); and that soot volume fractions may approximate universal fractions of mixture fraction in turbulent acetylene/air diffusion flames.

Flamelet Studies of Reduced and Detailed Kinetic Mechanisms for Methane/Air Diffusion Flames

2000 ◽  
Author(s):  
Foluso Ladeinde ◽  
Xiaodan Cai ◽  
Balu Sekar
Keyword(s):  
Dissipation Rate ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Intermediate Species ◽  
Flamelet Model ◽  
Mass Fractions ◽  
Kinetic Mechanisms ◽  
Moderate Effect ◽  
Extinction Strain Rate ◽  
Air Diffusion

We adopt a steady-state flamelet model in this paper to study the performance of reduced and detailed kinetic mechanisms for methane/air diffusion flames. Through the numerical calculations, we investigate the sensitivity of the main and intermediate species mass fractions to the mixture fraction dissipation rate, χ. Our results seem to suggest a weak to moderate effect of χ on the calculated species mass fraction. It has also been shown in this paper that the current flamelet calculations fail to predict the extinction strain rate.

The Civic: A Concept in Vortex Induced Combustion for the Solar Gemini 10 kW Gas Turbine

1981 ◽  
Vol 103 (1) ◽  
pp. 34-42 ◽  
Author(s):  
J. R. Shekleton
Keyword(s):  
Gas Turbine ◽  
Diffusion Flames ◽  
Reynolds Numbers ◽  
Flame Stabilization ◽  
Fuel Injector ◽  
Combustion Chambers ◽  
Turbine Generator ◽  
Fuel Injectors ◽  
Swirl Flame ◽  
Combustion Processes

The Radial Engine Division of Solar Turbines International, an Operating Group of International Harvester, under contract to the U.S. Army Mobility Equipment Research & Development Command, developed and qualified a 10 kW gas turbine generator set. The very small size of the gas turbine created problems and, in the combustor, novel solutions were necessary. Differing types of fuel injectors, combustion chambers, and flame stabilizing methods were investigated. The arrangement chosen had a rotating cup fuel injector, in a can combustor, with conventional swirl flame stabilization but was devoid of the usual jet stirred recirculation. The use of centrifugal force to control combustion conferred substantial benefit (Rayleigh Instability Criteria). Three types of combustion processes were identified: stratified and unstratified charge (diffusion flames) and pre-mix. Emphasis is placed on five nondimensional groups (Richardson, Bagnold, Damko¨hler, Mach, and Reynolds numbers) for the better control of these combustion processes.

Occurrence of Bubbles in a Thin Wire at Low Reynolds Number

1992 ◽  
Vol 114 (2) ◽  
pp. 255-260 ◽  
Author(s):  
K. Sato
Keyword(s):  
Separation Zone ◽  
Reynolds Numbers ◽  
Cavitation Number ◽  
The Other ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Thin Wires ◽  
Different Types ◽  
Low Reynolds ◽  
Air Diffusion

Thin wires of various diameters from 0.07 to 0.7 mm are examined about appearances and characteristics of bubble occurrence behind them in the range of low Reynolds numbers. The appearance of bubbles is very dependent on diameters of wires. Two different types of bubbles can be observed in the present experiment. One is a streamer-type bubble for smaller wires and the other is a small unspherical bubble for larger wires. The incipient and the desinent values of cavitation number also change greatly with the bubble types. The streamer-type bubble is related to the presence of laminar separation zone and the growth due to air diffusion. The small unspherical bubble can be mainly attributed to the motion of rolled-up vortices and the growth due to vaporization.

Greatly enhanced soot scattering in flickering CH4/Air diffusion flames

1993 ◽  
Vol 95 (1-2) ◽  
pp. 229-239 ◽  
Author(s):  
K SMYTH ◽  
J HARRINGTON ◽  
E JOHNSSON ◽  
W PITTS
Keyword(s):  
Diffusion Flames ◽  
Air Diffusion

A General Closure Model for the Time-Averaged Radiative Transfer Equation in Turbulent Flows

2010 ◽  
Author(s):  
Pedro J. Coelho
Keyword(s):  
Radiative Transfer ◽  
Turbulent Flows ◽  
Radiation Intensity ◽  
Transfer Equation ◽  
Radiative Transfer Equation ◽  
Mixture Fraction ◽  
Joint Probability ◽  
Turbulent Fluctuations ◽  
Proposed Model ◽  
Local Properties

The time-averaged form of the radiative transfer equation (RTE) includes emission and absorption correlations that need to be modeled. There is no general formulation to estimate the absorption coefficient-radiation intensity correlation, which is generally neglected (optically thin fluctuation approximation–OTFA). Here, a model to compute this correlation, as well as the other correlations in the time-averaged form of the RTE, is described. The formulation is based on the solution of two additional differential equations. The unclosed correlations in these equations are estimated assuming that the joint probability density function (pdf) of the radiation intensity and mixture fraction is a two-dimensional clipped Gaussian distribution. The model is applied to a turbulent jet diffusion flame, and a preliminary assessment of the model is reported. It is shown that fluctuations of the radiation intensity, caused by turbulence, imply the existence of a correlation between the radiation intensity and local properties. The assumption of the shape of the joint pdf of mixture fraction and radiation intensity yields satisfactory predictions if the turbulent fluctuations are moderate, but becomes inaccurate near the flame edge where turbulent fluctuations are very large. Nevertheless, the present results suggest that the proposed model may yield better predictions than the OTFA.

Sign in / Sign up

Export Citation Format

Share Document