Correlation of Turbulent Burning Velocity Data for Enclosed Flames
About: This article is published in Combustion Science and Technology.The article was published on 1978-11-01. It has received 2 citations till now.
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01 Jan 1981
TL;DR: In this article, a new approach to the correlation of turbulent burning velocity data is presented, which basically stems from the fact that detailed measurements of turbulence, using wire meshes and perforated discs as generators of isotropic turbulence, show a unique trend when the ratio of Kolmogorov microscale η to lateral macroscale L is plotted against the r.m.s.
Abstract: The present investigation highlights a new approach to the correlation of turbulent burning velocity data, which basically stems from the fact that detailed measurements of turbulence, using wire meshes and perforated discs as generators of isotropic turbulence, show a unique trend when the ratio of Kolmogorov microscale η to lateral macroscale L is plotted against the r.m.s. turbulent velocity u ′. For weak turbulence, the data obtained for different generators telescoped into a single curve, whereas for strong turbulence distinct demarcations could be detected for different grids. This cardinal finding was further pursued apropos of turbulent burning velocity data. Systematic measurements were carried out in cold flows using a hot-wire anemometer and a real time wave analyzer from which the requisite intensity and scales of turbulence were deduced. Subsequently burning velocity data for methane-air mixtures burning in an open burner were obtained by analyzing densitometrically the direct photographs of flames. Analysis reveals that two correlations are adequate for interpreting the data obtained. When turbulence intensity is low, the ratio of turbulent to laminar burning velocity S T /S L depends only on η/L in much the same fashion as u ′/S L while for large intensities, u ′/S L turns out to be an additional parameter besides η/L. When this analysis is extended to the data of other investigators, the forms of the correlating equations remain the same as in the present work but require different empirical constants. To sum up, it may be said that for weak turbulence η/L alone is adequate as a correlating parameter, while for strong turbulence both u ′/S L and η/L must be considered.
4 citations
01 Jan 1980
TL;DR: The influence of turbulence on combustion in open pre-mixed flames was studied in this paper, where the influence of the turbulence on the combustion in pre-mixed flames is discussed.
Abstract: The influence of turbulence on combustion in open pre-mixed flames " (1980). Retrospective Theses and Dissertations. Paper 7119.
1 citations
References
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TL;DR: In this article, the compatibility of theories of turbulence with different turbulent flame models is discussed, and it is suggested that the turbulent Reynolds number, Rλ, of the reactants is an important controlling parameter in turbulent flame propagation.
228 citations
TL;DR: In this paper, the influence of turbulence intensity, scale and vorticity on burning velocity and flame structure is examined by using premixed propane-air mixtures supplied at atmospheric pressure to a combustion chamber 31cm long and lOcmx 10 cm cross-section.
Abstract: The influence of turbulence intensity, scale and vorticity on burning velocity and flame structure is examined by using premixed propane-air mixtures supplied at atmospheric pressure to a combustion chamber 31cm long and lOcmx 10 cm cross-section. The chamber is fitted with transparent side walls to permit flame observations and schlieren photography. Control over the turbulence level is achieved by means of grids located upstream of the combustion zone. By suitable modifications to grid geometry and flow velocity, it is possible to vary turbulence intensity and scale independently within the combustion zone in such a manner that their separate effects on burning velocity and flame structure are readily distinguished. From analysis of the results obtained three distinct regions may be identified, each having different characteristics in regard to the effect of scale on turbulent burning velocity. For each region a mechanism of turbulent flame propagation is proposed which describes the separate influences on burning velocity of turbulence intensity, turbulence scale, laminar flame speed and flame thickness. The arguments presented in support of this 3-region model are substantiated by the experimental data and by the pictorial evidence on flame structure provided by the schlieren photographs. This model also sheds light on some of the characteristics which turbulent flames have in common with laminar flames when the latter are subjected to pressure and velocity fluctuations. Finally the important role of vorticity is examined and it is found that turbulent flame speed is highest when the rate of production of vorticity is equal to about half the rate of viscous dissipation.
114 citations
86 citations
01 Jan 1977
TL;DR: In this paper, the double kernel method was used to measure premixed hydrogen-air turbulent burning velocities, made by four high speed fans within the explosion vessel during explosions.
Abstract: Measurements are reported of premixed hydrogen-air turbulent burning velocities, made by the double kernel method during explosions. Turbulence was created by four high speed fans within the explosion vessel. The method is described for calibrating the system, which is capable of giving high values of turbulent Reynolds numbers. The values obtained are compared with those of many other workers, over a wide range of burning conditions, mixtures and turbulent parameters. The ratio of turbulent to laminar burning velocity correlates well with both the turbulent Reynolds number and the ratio of laminar burning velocity to r.m.s. turbulent velocity. The use of hydrogen-air mixtures has extended the data on premixed turbulent combustion to regimes with higher values of the last dimensionless ratio. At high values of the ratio there is evidence of a wrinkled laminar flame structure, but at lower values a small scale eddy structure seems to be dominant. There is discussion on these findings, which accord with theoretical expectations.
74 citations
TL;DR: In this paper, Schlieren photographs were taken through transparent side walls at turbulence levels ranging from 2 to 14 per cent and at velocities up to 250 ft/sec.
50 citations