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1.
粉尘湍流火焰诱导激波问题是工业灾害研究中的重要课题.本文在自行设计的大型卧式燃烧管内,对铝粉火焰诱导激波现象进行了实验研究,测试了湍流火焰阵面前压缩波到激波的转捩过程,并将实验结果与数值模拟结果进行了比较. 相似文献
2.
微重力燃烧基础研究概述 总被引:2,自引:2,他引:0
本文介绍了国外微重力燃烧基础研究的概况。在微重力条件下不存在浮力和由其引起的自然对流,从而影响了燃烧基本过程。理论和实验研究表明,在微重力条件下火焰结构,火焰传播,火焰稳定等一系列燃烧基本过程都明显不同于通常在地球表面上所观察到的现象。 相似文献
3.
方形管内楔形障碍物对火焰结构与传播的影响 总被引:1,自引:0,他引:1
通过实验与数值模拟方法对CH4/空气预混火焰在有楔形障碍物的卧式燃烧方管内的传播进行了研究。采用多镜头Cranz Schardin高速摄像机和压力传感器等实验设备获得了高清晰度的障碍物诱导火焰失稳的分幅时序照片以及障碍物背风表面压力变化曲线。数值模拟则基于RANS方法与EDU-Arrhenius燃烧模型,计算结果与实验结果基本相符,反映了火焰在管内传播与变形的详细过程。通过综合分析实验与计算结果,得到了由楔形障碍物导致的火焰加速与变形的内在机理,揭示了火焰传播过程中由层流燃烧向湍流燃烧转捩的本质。 相似文献
4.
微重力条件下固体材料的着火和火焰传播特性研究对于发展燃烧理论、保障航天器防火安全具有重要意义.由于地面设施微重力时间长度的限制,已有对微重力下材料燃烧过程的实验研究主要集中在热薄材料,而关于热厚材料的实验结果十分有限.作为实践十号(SJ-10)卫星科学实验项目之一,非金属材料燃烧实验将利用长时间微重力条件开展低速流动中典型热厚材料着火和火焰传播过程研究.简要介绍非金属材料燃烧项目的研究目标、空间实验内容、有效载荷技术特点和地面实验验证情况. 相似文献
5.
本文建立了C6H12N6+KClO4+Mg+SrSO4固相振荡燃烧体系的非吸热三变量立方自催化化学模型,应用非线性数学分析方法,研究了固相振荡的化学动力学机理,并对此进行了数值模拟,结果反映了这一振荡燃烧体系所具有的非线性化学动力学特性。 相似文献
6.
微重力流体科学是流体力学与空间材料、空间生物技术、燃烧交叉的新兴学科.研究微重力环境中流体的流动、迁移,热、质输运和相变等基本规律,还有物理化学问题和低温问题,这是微重力科学的基础和核心近三十年来,随着空间技术的进步,空间科学迅速发展.空间飞行器在轨道自由飞行时,其间的微重力水平仅为地面的10~-3~10~-6量级,在地面重力作用下常见的浮力对流、静压不均匀和沉降等现象都极大地减弱.因此,有可能利用微重力条件得到在地面条件下难于得到的高质量生物制品和新材料.但是,在微重力环境中,许多在地面上的次级… 相似文献
7.
微重力燃烧研究进展 总被引:5,自引:0,他引:5
认识燃烧过程是安全、高效、洁净地利用能源的基础. 但是, 常重力条件下的浮力对流和重力沉降使得燃烧现象变得复杂. 而微重力条件下这些影响几乎消失, 这简化了对燃烧的研究. 在加深对地面燃烧过程和载人航天器火灾安全问题的认识的推动下, 经过近半个世纪特别是最近10多年的发展, 微重力燃烧研究已经涵盖了预混气体、气体扩散、液滴、颗粒和粉尘燃烧、燃料表面的火焰传播等燃烧学科的各个领域. 研究中实现了球对称液滴燃烧、不受沉降影响的粉尘燃烧、静止或低速对流环境中的燃烧, 观察到了火球、自熄灭火焰等现象,阐明了碳黑形成中的热泳力效应、可燃极限与火焰稳定性等机理. 加深了对燃烧现象,特别是对辐射效应的理解: 在预混气体、气体扩散、液滴等多种火焰中, 除了停留时间过短引起的吹熄极限外, 还存在辐射热损失过大引起的冷熄极限, 后者只能在微重力条件下观测到. 部分研究成果已经进入教材. 而火焰在微重力下不同于常重力下的现象, 对载人航天器火灾安全具有重要意义. 考虑到我国的现实情况和国内外的研究现状, 建议将煤炭颗粒和粉尘的燃烧、与碳黑相关的机理、辐射效应、化学动力学等作为我国微重力燃烧的主要研究方向. 相似文献
8.
本文基于颗粒相的轨道模型,对大速差射流燃烧室中烟煤粉与贫煤粉的二维流动,混合及燃烧进行了数值模拟,模拟结果从两相耦合的角度,阐明了煤粉颗粒在燃烧室中运动的规律,煤粉与大速差射流诱导的中心气体逆流之间的混合及其对煤粉火焰稳定的影响,指出此种燃烧室中煤粉火焰稳定的回流区燃烧机理,气相流场及回流区的预报结果与实验符合良好。 相似文献
9.
微重力下薄燃料表面火焰传播的地面窄通道模拟 总被引:1,自引:0,他引:1
对微重力下薄燃料表面逆风火焰传播的地面窄通道模拟,进行了量纲分析,并通过火焰传播
图像记录进行了实验验证. 结果表明,减小实验段特征尺寸可以实现微重力燃烧的地面模拟.
在各种氧气浓度条件下,竖直和水平窄通道内的火焰传播速度随气流速度的变化趋势完全不
同,而且,水平窄通道可以有效限制自然对流,而竖直窄通道较难. 当通道高度增大时,竖
直和水平窄通道中,火焰传播速度和吹熄极限速度都不同程度地增大,这是热损失减小、火
焰面遇见的气流速度减小以及自然对流速度增大3个因素的综合结果. 对于水平窄通道,
1cm是一个可以定性模拟微重力下自然对流的尺寸. 对于竖直窄通道,则需要高度更小的窄通
道来限制自然对流. 相似文献
10.
11.
Experimental investigation of flame/solid interactions in turbulent premixed combustion 总被引:5,自引:0,他引:5
Salah S. Ibrahim Graham K. Hargrave Tim C. Williams 《Experimental Thermal and Fluid Science》2001,24(3-4):99-106
An experimental study has been carried out to investigate the interaction between propagating turbulent premixed flames and solid obstacles. The experimental rig was configured specifically to allow detailed measurements with laser-based optical diagnostics. A wall-type solid obstacle was mounted inside a laboratory-scale combustion chamber with rectangular cross-section. The flame was initiated, by igniting a combustible mixture of methane in air at the center of the closed end of the combustion chamber. The flame front development was visualized by a high-speed (9000 frame/s) digital video camera and flame images were synchronized with ignition timing and chamber pressure data. The tests were carried out with lean, stoichiometric and rich mixtures of methane in air. The images were used to calculate highly resolved temporal and spatial data for the changes in flame shape, speed, and the length of the flame front. The results are discussed in terms of the influence of mixture equivalence ratio on the flame structure and resulting overpressure. The reported data revealed significant changes in flame structure as a result of the interaction between the propagating flame front and the transient recirculating flow formed behind the solid obstacle. Combustion images show that the flame accelerates and decelerates as it impinges on the obstacle wall boundaries. It is also found that the mixture concentrations have a significant influence on the nature of the flame/solid interactions and the resulting overpressure. The highest flame speed of 40 m/s was obtained with the unity fuel–air equivalence ratio. Burning of trapped mixture behind the solid obstruction was found to be highly correlated with the flame front length and the rate of pressure rise. 相似文献
12.
13.
Numerical simulation of convective heat transfer to a radial free surface jet impinging on a hot solid 总被引:1,自引:0,他引:1
The convective heat transfer between a circular free surface impinging jet and a solid surface has been studied numerically.
The thin liquid film formed on the surface has been assumed to be in non-turbulent free surface flow. The effects of surface
tension, viscosity, gravity and heat transfer between the film flow and the solid surface have been taken into account. The
flow structure on a non-heated surface has been investigated first. Next, the steady-state flow structure in the liquid film
as well as the heat transfer has been examined. The predicted results have been compared with experimental data for the purpose
of validating the analysis. The hydrodynamics of the liquid film and the heat transfer processes have been investigated numerically
to understand the physics of the phenomena.
Received on 5 October 1998 相似文献
14.
Large-scale strain rate field, a resolved quantity which is easily computable in large-eddy simulations (LES), could have profound effects on the premixed flame properties by altering the turbulent flame speed and inducing local extinction. The role of the resolved strain rate has been investigated in a posterior LES study of GE lean premixed dry low-NOx emissions LM6000 gas turbine combustor model. A novel approach which is based on the coupling of the linear-eddy model with a one-dimensional counterflow solver has been applied to obtain the parameterizations of the resolved premixed flame properties in terms of the reactive progress variable, the local strain rate measure, and local Reynolds and Karlovitz numbers. The strain rate effects have been analyzed by comparing LES statistics for several models of the turbulent flame speed, i.e, with and without accounting for the local strain rate effects, with available experimental data. The sensitivity of the simulation results to the inflow velocity conditions as well as the grid resolution have been also studied. Overall, the results obtained demonstrate that the effects of the resolved strain rate are not dominant for the considered premixed flame configuration and the unstrained turbulent flame speed model is found to perform as well as the one that allows for the strain rate effects. 相似文献
15.
A swirl-stabilised, lean, partially premixed combustor operating at atmospheric conditions has been used to investigate the
local curvature distributions in lifted, stable and thermoacoustically oscillating CH4-air partially premixed flames for bulk cold-flow Reynolds numbers of 15,000 and 23,000. Single-shot OH planar laser-induced
fluorescence has been used to capture instantaneous images of these three different flame types. Use of binary thresholding
to identify the reactant and product regions in the OH planar laser-induced fluorescence images, in order to extract accurate
flame-front locations, is shown to be unsatisfactory for the examined flames. The Canny-Deriche edge detection filter has
also been examined and is seen to still leave an unacceptable quantity of artificial flame-fronts. A novel approach has been
developed for image analysis where a combination of a non-linear diffusion filter, Sobel gradient and threshold-based curve
elimination routines have been used to extract traces of the flame-front to obtain local curvature distributions. A visual
comparison of the effectiveness of flame-front identification is made between the novel approach, the threshold binarisation
filter and the Canny-Deriche filter. The novel approach appears to most accurately identify the flame-fronts. Example histograms
of the curvature for six flame conditions and of the total image area are presented and are found to have a broader range
of local flame curvatures for increasing bulk Reynolds numbers. Significantly positive values of mean curvature and marginally
positive values of skewness of the histogram have been measured for one lifted flame case, but this is generally accounted
for by the effect of flame brush curvature. The mean local flame-front curvature reduces with increasing axial distance from
the burner exit plane for all flame types. These changes are more pronounced in the lifted flames but are marginal for the
thermoacoustically oscillating flames. It is concluded that additional fuel mixture fraction and velocimetry studies are required
to examine whether processes such as the degree of partial-premixedness close to the burner exit plane, the velocity field
and the turbulence field have a strong correlation with the curvature characteristics of the investigated flames. 相似文献
16.
This paper presents pore scale simulation of turbulent combustion of air/methane mixture in porous media to investigate the effects of multidimensionality and turbulence on the flame within the pores of porous media. In order to investigate combustion in the pores of porous medium, a simple but often used porous medium consisting of a staggered arrangement of square cylinders is considered in the present study. Results of turbulent kinetic energy, turbulent viscosity ratio, temperature, flame speed, convective heat transfer and thermal conductivity are presented and compared for laminar and turbulent simulations. It is shown that the turbulent kinetic energy increases from the inlet of burner, because of turbulence created by the solid matrix with a sudden jump or reduction at the flame front due to increase in temperature and velocity. Also, the pore scale simulation revealed that the laminarization of flow occurs after flame front in the combustion zone and turbulence effects are important mainly in the preheat zone. It is shown that turbulence enhances the diffusion processes in the preheat zone, but it is not enough to affect the maximum flame speed, temperature distribution and convective heat transfer in the porous burner. The dimensionless parameters associated with the Borghi–Peters diagram of turbulent combustion have been analyzed for the case of combustion in porous media and it is found that the combustion in the porous burner considered in the present study concerns the range of well stirred reactor very close to the laminar flame region. 相似文献
17.
The effects of mean flame radius and turbulence on self-sustained combustion of turbulent premixed spherical flames in decaying
turbulence have been investigated using three-dimensional direct numerical simulations (DNS) with single step Arrhenius chemistry.
Several flame kernels with different initial radius or initial turbulent field have been studied for identical conditions
of thermo-chemistry. It has been found that for very small kernel radius the mean displacement speed may become negative leading
ultimately to extinction of the flame kernel. A mean negative displacement speed is shown to signify a physical situation
where heat transfer from the kernel overcomes the heat release due to combustion. This mechanism is further enhanced by turbulent
transport and, based on simulations with different initial turbulent velocity fields, it has been found that self-sustained
combustion is adversely affected by higher turbulent velocity fluctuation magnitude and integral length scale. A scaling analysis
is performed to estimate the critical radius for self-sustained combustion in premixed flame kernels in a turbulent environment.
The scaling analysis is found to be in good agreement with the results of the simulations. 相似文献
18.
19.
The processes of interaction between concentrated energy fluxes and solid targets have been investigated in a number of studies.
The generation of magnetic fields in erosional plasma formations has been experimentally observed [1–4]. However, the evolution
of magnetic fields in plasma jets has not yet been studied in sufficient detail. This paper is devoted to a numerical investigation
of unsteady three-dimensional erosion plasma flows and the generation in those flows of magnetic fields resulting from the
action of laser radiation on solid targets.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 135–140, November–December, 1986.
The authors are grateful to I. V. Nemchinov and B. T. Fedyushin for useful discussion of their results. 相似文献
20.
粒状火药床燃烧转爆轰的研究 总被引:2,自引:0,他引:2
以多-45火药为研究对象,采用离子探针测速和应变片测压的技术,对强约束(钢管)条件下火药颗粒床燃烧转爆轰全过程中的火焰烽和压缩波进行了测量。提出了粒状火药燃烧转爆轰的机理。还研究了不同实验条件下火药燃烧转爆轰的敏感性。 相似文献