The structure and propagation of turbulent flames
24 Jun 1975-Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences (The Royal Society)-Vol. 344, Iss: 1637, pp 217-234
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.
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TL;DR: A review of the current state of the art in turbulent combustion modelling can be found in this article, where the authors present physical and experimental knowledge of the structure of turbulent flames in order to help the further discussions of models on a physical basis.
572 citations
TL;DR: Several models have been suggested utilizing this approach and the first laboratory and industrial applications of them have shown encouraging results as mentioned in this paper, and these successful applications motivate a thorough discussion and further development of the approach.
517 citations
TL;DR: In this article, a dimensionless power spectral density function is presented, and used to show how both effective r.m.s. turbulent velocity and flame straining rate develop in an explosion.
Abstract: All known experimental values of turbulent burning velocity have been scrutinized. These number 1650, a significant proportion of which at the higher turbulent Reynolds numbers we measured in a fan-stirred bomb. Dimensionless correlations which have a theoretical basis are presented. These are in terms of flame straining rates and the effective r.m.s. turbulent velocity, as well as the laminar burning velocity of the mixture. When a flame develops from an ignition source it is not initially exposed to the lower frequencies of the turbulent spectrum. As the kernel grows the flame is affected by ever-lower frequencies and the turbulent burning velocity increases towards a fully developed value. An experimental dimensionless power spectral density function is presented, and used to show how both effective r.m.s. turbulent velocity and flame straining rate develop in an explosion. The results are relevant to a variety of practical devices, including gasoline engines, as well as atmospheric explosions.
378 citations
01 Jan 1985
TL;DR: The physical structure of turbulent flames cannot be regarded as completely understood at present due to the complexity of relevant experimentation as discussed by the authors, however, many prediction methods have been proposed in recent years, and at the same time much experimental investigation has been performed.
Abstract: Turbulent combustion occurs in a majority of industrial devices. Many prediction methods have been proposed in recent years, and at the same time much experimental investigation has been performed. However, the physical structure of turbulent flames cannot be regarded as completely understood at present due to the complexity of the relevant experimentation.
373 citations
TL;DR: In this article, a dimensionless correlation of experimental values of turbulent burning velocities is presented and a distribution function of stretch rates in turbulent flames is proposed and the experimental data are well predicted by a theory based on flamelet extinction by flame stretch with this distribution.
Abstract: A rational basis for correlating turbulent burning velocities is shown to involve the product of the Karlovitz stretch factor and the Lewis number. A generalized expression is derived to show how flame stretch is related to the velocity field. A new dimensionless correlation of experimental values of turbulent burning velocities is presented. Dimensionless groups also are used in correlations of laminar and turbulent flame extinction stretch rates. A distribution function of stretch rates in turbulent flames, based on an earlier one of Yeung et al ., is proposed and the experimental data are well predicted by a theory based on flamelet extinction by flame stretch with this distribution. Uncertainties arise concerning the role of negative stretch rate. Laminar flamelet modelling of complex combustion appears to have a broader validity than might be expected and some explanation for this is offered.
295 citations
Cites methods from "The structure and propagation of tu..."
...Bray (1990) has used a flamelet analysis based on the Bray-Libby-Moss (1985) model to derive an expression for the ut/u, ratio, which he compared with the experimental data of Abdel-Gayed et al....
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TL;DR: In this paper, it was shown that turbulent flame speed increases with scale under conditions of weak turbulence and decreases with increase in scale under condition of strong turbulence, and the two regions are separated by a transition region, which occurs when the turbulence intensity is about twice the laminar flame speed.
41 citations