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51.
52.
P. Anselmo-Filho S. Hochgreb R.S. Barlow R.S. Cant 《Proceedings of the Combustion Institute》2009,32(2):1763-1770
Combustion under stratified conditions is common in many systems. However, relatively little is known about the structure and dynamics of turbulent stratified flames. Two-dimensional imaging diagnostics are applied to premixed and stratified V-flames at a mean equivalence ratio of 0.77, and low turbulent intensity, within the corrugated flame range. The present results show that stratification affects the mean turbulent flame speed, structure and geometric properties. Stratification increases the flame surface density above the premixed flame levels in all cases, with a maximum reached at intermediate levels of stratification. The flame surface density (FSD) of stratified flames is higher than that of premixed flames at the same mean equivalence ratio. Under the present conditions, the FSD peaks at a stratification ratio around 3.0. The FSD curves for stratified flames are further skewed towards the product side. The distribution of flame curvature in stratified flames is broader and more symmetric relative to premixed flames, indicating an additional mechanism of curvature generation, which is not necessarily due to cusping. These experiments indicate that flame stratification affects the intrinsic behaviour of turbulent flames and suggest that models may need to be revised in the light of the current evidence. 相似文献
53.
A question of flow around an obstacle leads to an optimal control problem. If an optimum path exists, then it is calculable from the Pontryagin principle. The optimum is verified to be reached, using a discretization of the problem. 相似文献
54.
双圆弧扦值算法又一法——坐标法 总被引:1,自引:0,他引:1
本文介绍的方法是用坐标来进行计算 ,既方便 ,又可行 .用一组首尾相接彼此相切的园弧段去逼近给定的曲线使机床切割的机件或计算机绘制的图形进一步满足精度要求 . 相似文献
55.
Uri. Goldberg 《International Journal of Computational Fluid Dynamics》2013,27(1):27-38
A new topography-parameter-free turbulence closure, based on a transport equation for the pseudo eddy viscosity, is described. The model is tested against experimental data of several flow cases across the Mach number range and compared to Menter's single equation model and to the Spalart-Allmaras model. The main conclusion is that the new closure outperforms the other two models in both low and high speed flows. 相似文献
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Level-set G-equation and stationary flamelet chemistry are used in large eddy simulation of a propane/air premixed turbulent flame stabilized by a bluff body. The aim was to study the interaction between the flame front and turbulent eddies, and in particular to examine the effect of sub-grid scale (SGS) eddies on the wrinkling of the flame surface. The results indicated that the two types of turbulence eddies—the resolved large scale eddies and the unresolved SGS eddies—have different effects on the flame. The fluctuation of the flame surface, which is responsible for the broadening of the time averaged mean flame brush by turbulence, depends on the large resolved turbulence eddies. Time averaged mean flow velocity, temperature, and major species concentrations mainly depend on the large scale resolved eddies. The unresolved SGS eddies contribute to the wrinkling at the SGS level and play an important role in the enhancement of the propagation speed of the resolved flame front. In addition, the spatially filtered intermediate species, such as radicals, and the spatially filtered reaction rates strongly depend on the small SGS eddies. The asymptotic behavior of flame wrinkling by the SGS eddies, with respect to the decrease in filter size and grid size, is investigated further using a simplified level-set equation in a model shear flow. It is shown that to minimize the influence of the SGS eddies, fine grid and filter size may have to be used. 相似文献
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60.
A high-speed photographic study of the transition from deflagration to detonation wave 总被引:2,自引:0,他引:2
Experiments were conducted to investigate the DDT process of the oxyhydrogen gas in the rectangular detonation tube of 3 m
long. The repeated obstacle was installed near the ignition plug and the effects of the obstacle on the DDT process were investigated.
The behaviour of the combustion and detonation wave were visualized utilizing Imacon high-speed camera with the aid of Schlieren
optics.
As a result, DDT process was visualized, i.e. (i) multiple shock waves were induced by the expanding combustion wave, because
the combustion flame played a role as a piston and compressed the unburned gases. (ii) The acceleration of the combustion
wave was occurred and the distance between the shock wave and the combustion flame became shorter. (iii) Eventually, the local
explosion was occurred and cause overdriven detonation wave to propagate at the velocity of about 3 kms−1.
An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Boulder, Colorado, from July 30 to August 4, 1995 相似文献