Dependence of turbulent burning velocity on turbulent reynolds number and ratio of flaminar burning velocity to R.M.S. turbulent velocity
01 Jan 1977-Vol. 16, Iss: 1, pp 1725-1735
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.
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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
TL;DR: In this article, experimental data and results of direct numerical simulations are reviewed in order to show that premixed combustion can change the basic characteristics of a fluctuating velocity field (the so-called flame-generated turbulence) and the direction of scalar fluxes (the countergradient or pressure-driven transport) in a turbulent flow.
212 citations
TL;DR: In this paper, the authors measured the burning velocities of an explosion bomb equipped with four high speed fans using laser doppler anemometry and showed that the turbulent Reynolds numbers were significantly higher than in most previous measurements and high rates of strain were achieved until several of the flames quenched.
Abstract: Turbulent burning velocities have been measured in an explosion bomb equipped with four high speed fans. Turbulent parameters were measured by laser doppler anemometry. The turbulent Reynolds numbers were significantly higher than in most previous measurements and high rates of strain were achieved until, ultimately, several of the flames quenched. Results are presented in terms of previously used dimensionless parameters plus a Lewis number and a dimensionless activation energy. The two-eddy theory of burning can allow for flame straining reductions in laminar burning velocity and experimental values of u t / u 1 were compared with those from such a theory.
205 citations
TL;DR: In this article, the authors surveyed available experimental data on the turbulent burning velocity of premixed gases and discussed the accuracy of experimental measurements and the means of ascertaining relevant turbulent parameters.
Abstract: Available experimental data on the turbulent burning velocity of premixed gases are surveyed. There is discussion of the accuracy of experimental measurements and the means of ascertaining relevant turbulent parameters. Results are presented in the form of the variation of the ratio of turbulent to laminar burning velocities with the ratio of r.m.s. turbulent velocity to laminar burning velocity, for different ranges of turbulent Reynolds number. A two-eddy theory of burning is developed and the theoretical predictions of this approach, as well as those of others, are compared with experimentally measured values.
113 citations
References
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TL;DR: In this paper, an improved approximation to spatially homogeneous turbulent shear flow is presented, which allows direct estimation of all components of the turbulent pressure/velocity-gradient tensor, which accounts for inter-component energy transfer and helps to regulate the turbulent stress.
Abstract: With a transverse array of channels of equal widths but differing resistances, we have generated an improved approximation to spatially homogeneous turbulent shear flow. The scales continue to grow with downstream distance, even in a region where the mean velocity gradient and one-point turbulence moments (component energies and shear stress) have attained essentially constant values. This implies asymptotic non-stationarity in the basic Eulerian frame convected with the mean flow, behaviour which seems to be inherent to homogeneous turbulent shear flow.Two-point velocity correlations with space separation and with space-time separation yield characteristic departures from isotropy, including clear ‘upstream–downstream’ unsymmetries which cannot be classified simply as axis tilting of ellipse-like iso-correlation contours.The high wave-number structure is roughly locally isotropic although the turbulence Reynolds number based on Taylor ‘microscale’ and r.m.s. turbulent velocity is only 130. Departures from isotropy in the turbulent velocity gradient moments are measurable.The approximation to homogeneity permits direct estimation of all components of the turbulent pressure/velocity-gradient tensor, which accounts for inter-component energy transfer and helps to regulate the turbulent shear stress. It is found that its principal axes are aligned with those of the Reynolds stress tensor. Finally, the Rotta (1951, 1962) linear hypothesis for intercomponent energy transfer rate is roughly confirmed.
448 citations
TL;DR: In this paper, the variation of burning velocity with equivalence ratio for methane-air mixtures at one atmosphere pressure values were determined by the bombhot wire and corrected density ratio techniques, for combustion during the prepressure period.
431 citations
01 Jan 1951
TL;DR: A detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented in this article, where mean speed and axial-fluctuation measurements were made well within the laminar sublayer.
Abstract: A detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 12,300, 30,800, and 61,600, based on the half width of the channel and the maximum mean velocity. A channel of 5-inch width and 12:1 aspect ratio was used for the investigation. Mean-speed and axial-fluctuation measurements were made well within the laminar sublayer. The semitheoretical predictions concerning the extent of the laminar sublayer were confirmed. The distribution of the velocity fluctuations in the direction of mean flow u' shows that the influence of the viscosity extends farther from the wall than indicated by the mean velocity profile, the region of influence being approximately four times as wide.
349 citations
254 citations
TL;DR: In this paper, a theory of turbulent burning velocity has been developed to explain the production of turbulence by the turbulent flame and a comparison of calculated maximum turbulence intensity values with the turbulence intensities that correspond to the measured turbulent burning•velocity data supports this theory.
Abstract: A new theory of turbulent burning velocity has been developed. Comparison of the predictions of the theory with turbulent burning‐velocity measurements has led to recognition that the turbulent flame itself generates additional turbulence. A theory has been formulated to explain the production of turbulence by the turbulent flame, which permits calculation of the intensity of flame generated turbulence. A comparison of calculated maximum turbulence intensity values with the turbulence intensities that correspond to the measured turbulent burning‐velocity data supports this theory.
242 citations