竖直射流火撞击障碍管道数值模拟分析

当前对于竖直向上屏障射流火的研究大多集中于顶棚射流,对于竖直向上射流火羽流撞击管道的研究相对较少。为研究竖直向上射流火羽流撞击管道的特征演化行为,基于燃烧学及流体力学基本原理,运用Fluent数值模拟软件,通过控制变量法对不同热释放速率、障碍管道直径及管壁-火源间距因素进行探究。研究表明障碍管道直径和管壁-火源间距对火焰高度和宽度均有一定程度的影响,且得到了基于Froude数的无量纲火焰高度表征模型。     

撞击流对火焰稳定性影响的试验研究

研究了射流火焰噪声和撞击式火焰噪声,对比两者以探求撞击流对火焰稳定性的影响。对火焰噪声信号进行频谱分析（FFT）,结果表明,射流火焰噪声包含燃烧噪声和喷流噪声,火焰噪声以燃烧噪声为主,撞击式火焰噪声是主频约420Hz的高频噪声,由燃烧噪声、喷流噪声和撞击区燃烧噪声组成。撞击式火焰噪声频谱图表明,撞击流强化了气化燃烧,有利于火焰的稳定,对气化炉的稳定运行有重大意义。     

两喷嘴对置撞击流径向射流流动特征

对喷嘴间距与喷嘴直径比为0.5～100范围内两喷嘴对置撞击流径向射流的湍流脉动特征、速度分布和扩展率等进行了实验研究和数值模拟。研究结果表明,撞击流径向射流明显较自由射流湍动强烈;从驻点开始径向射流速度逐渐增大到最大值后开始衰减,射流呈现自相似性;随着喷嘴间距增大,撞击流径向射流的扩展率呈现增大的趋势,大约为自由圆射流的1.5～3倍。采用CFD软件对撞击流径向射流的速度分布特征进行了数值模拟,与实验结果相比,两方程湍流模型预报的撞击流径向射流的扩展率明显偏小,雷诺应力模型的预报精度有较大改进。     

气固射流扩散火焰形态研究

利用文丘里效应,自行设计气固射流扩散火焰（气固喷射火）实验装置,分别采用147 μm和178 μm两种粒径均匀的白色石英砂以近似恒定速率卷吸入火焰中,来研究固体颗粒对火焰形态的影响,特别地,通过关闭侧面进砂口所形成的气态射流扩散火焰（气态喷射火）与之相比较。理论分析和实验结果表明,砂子进入火焰中会降低火焰温度,并且粒径为147 μm的砂子进入火焰的质量大于178 μm砂子,导致小粒径气固喷射火具有更低的火焰温度,从而具有更低的层流燃烧速度和更大的火焰Froude数,最终使其具有更高的推举高度和火焰高度。对比分析气固喷射火和气态喷射火实验结果,也表明固体颗粒对火焰温度的冷却作用导致气固喷射火更容易产生推举现象并具有更高的火焰高度。     

微喷管氢气非预混射流火焰燃烧特性

采用考虑详细化学反应机理的数值计算,对空气伴流中微圆管氢气非预混射流火焰进行了研究。不同流速下火焰OH基元分布数值计算与实验结果吻合较好。结果表明：当微圆管内径保持不变时,随着燃料速度减小,火焰最高温度逐渐降低。当燃料速度接近熄灭极限速度时,火焰最高温度开始急剧下降;微圆管氢气非预混射流火焰存在最小流速对应的熄灭极限;随着管壁材料热导率降低,火焰中心轴线上的最高温度逐渐升高,喷口处壁面温度也升高;管壁材料热导率对火焰熄灭极限速度影响不显著。     

储罐壁面限制条件下喷射火火焰行为

高压燃气储罐泄漏极易诱发喷射火。通过搭建储罐壁面限制条件下不同喷射角度的喷射火实验装置,对近喷口流场受限的喷射火进行了系统研究,并验证了装置测试的可重复性。实验结果表明,储罐壁面限制条件下推举高度小于自由射流的推举高度,并通过数值模拟分析了两种空间条件下空气卷吸流场的差异性,从而物理解释了储罐壁面限制条件对推举高度的影响。两种空间条件下火焰长度都随喷射角度的增加而减小,但自由垂直射流的火焰长度小于储罐壁面限制条件下的火焰长度。火焰行为由浮力控制转为动量控制的临界Froude数与喷射角度和空间限制条件无关。研究还发现,与自由射流相比,储罐壁面的阻塞效应会降低火焰的推举速度,提高火焰的吹熄速度。     

基于PLIF的浸没撞击流反应器的混合特性

利用平面激光诱导荧光技术对水平两喷嘴液-液撞击流反应器内的浓度场进行定性和定量分析,用离析度(IOS)评价时均混合效果,得到不同操作条件下IOS值沿径向射流方向的变化规律,并与三喷嘴的情况进行对比. 结果表明,喷嘴间距L、喷嘴直径D和进口流量Q对反应器混合效果有重要影响,在水平两向撞击流中,当喷嘴直径和流量一定时,随喷嘴间距增大,IOS下降速度加快,最佳间距为L/D=3;当喷嘴间距和流量一定时,随喷嘴直径增大,IOS下降更快,下降到IOS=0.05所需距离不断减小,最佳喷嘴直径D=12 mm;当喷嘴直径和喷嘴间距一定时,随流量增加,IOS下降速度先增加后减小,最佳流量Q=500′10-3 m3/h. 三喷嘴撞击流与两喷嘴变化趋势一致.     

双组分层撞击流反应器浓度场混沌分析

采用平面激光诱导荧光技术测量双组分层式撞击流反应器撞击区浓度分布,利用混沌理论分析不同喷嘴间距、喷嘴直径和射流雷诺数下撞击流反应器浓度场混沌特征参数(关联维、Kolmogorov熵和最大Lyapunov指数)的变化规律。结果表明,撞击流反应器内浓度场混沌特征参数随喷嘴间距的增大呈上下波动的变化趋势,Kolmogorov熵在L=2d时达到最大。浓度场混沌特征参数随喷嘴直径增大呈上下波动的变化趋势,Kolmogorov熵在d=8 mm时整体上最大;射流雷诺数为Re=22 000时整体上混沌特征参数最佳。受二次撞击区的影响,撞击面上靠近二次撞击区各点的混沌特征参数有明显提高。     

撞击流反应器混合性能研究进展

按照撞击流反应器的研究发展进程,分析了撞击流反应器的混合过程。结合大量学者研究工作,回顾了反应空间、流体流动、喷嘴结构等因素对常见的开放式撞击流反应器、受限撞击流反应器、浸没循环撞击流反应器等反应器混合性能影响的研究。简述了外界激励和其他技术对撞击流反应器混合效果影响的研究进展,并总结了几类反应器的微观混合时间及关联式。同时介绍了一种新型水平三向撞击流反应器,该反应器产生的径向射流不同于两喷嘴径向射流,而为交叉状的伞状射流;通过进一步探究发现当量喷嘴间距L*=2 D~3 D时径向射流偏转角β出现峰值,而且此时的混合时间也最短。最后对撞击流反应器混合性能研究前景进行展望。     

坑道限制条件下水平丙烷喷射火火焰行为研究

通过搭建坑道限制条件下小尺寸喷射火实验装置,模拟研究埋地管道泄漏场景中引发的水平喷射火火焰特性。火焰受坑道侧壁的限制,先撞击坑道而后沿着侧壁向上发展形成垂直火焰。实验结果表明,随着泄漏质量流量的增加,火焰长度先增加后减小,而火焰宽度不断增加。同时发现,在一定条件下火焰两侧会出现涡旋对,形成一对反向旋转的火焰,为了探究其形成原因及产生条件,结合数值模拟手段进一步研究了火焰流场不稳定性。     

Computational investigation of flame extension height for horizontally oriented rectangular source jet fires impinging on a vertical plate

This paper investigates the flame extension height induced by a horizontally oriented rectangular source fire impinging on a vertical plate, which has rarely been reported in literature. Focusing on the scenarios with nonimpinging flame lengths that are comparable with or larger than the plate‐source distance, a series of numerical experiments were conducted, in which the exit velocities varied from 27.5 to 125 m/s and the orifice aspect ratios ranged from 1 to 4. Results show that the flame extension height increases with increasing exit velocity and becomes larger with increasing orifice aspect ratio at a given fuel exit velocity. New correlations are proposed to predict the flame extension height based on the unburnt fuel after impinging, assuming a kite flame shape of circular and elliptical cross section. Moreover, the new proposed correlations provide a general and practical basis for estimating the flame extension height of horizontally oriented rectangular source impinging jet fires.     

Impact of flat roof–integrated solar photovoltaic installation mode on building fire safety

This paper quantifies experimentally the fire‐induced reradiation to roof surface created by flame extension on the back of the flat roof–integrated photovoltaic (PV) array. A gas burner underneath the tilted PV panels was employed as the fire source. The effects of the PV tilt angle, distance from PV panel to roof, and fire heat release rate (HRR) were investigated. The flame extension geometries and flame reradiation heat flux distribution were recorded. The results show that the flame extension length and vertical thickness (ie, the vertical distance from the back surface of the PV panel to the extension flame profile) are reduced with the increase of PV tilt angle and panel‐roof distance but are increased with increases in the fire HRR. A unified nondimensional HRR coupled with all these factors is proposed to quantify the flame extension geometry. Furthermore, a general equation based on the physical relationship between flame radiation and flame geometry is developed to characterize the distribution of reradiation heat flux on the roof surface with the nondimensional local flame thickness. Finally, suggestions regarding PV installations on flat roofs and the selection of roofing materials are given to decrease the possibility of flame propagation underneath the PV arrays.     

高压可燃气体泄漏动力学过程与喷射火热灾害分析

以高压可燃气体泄漏诱发的喷射火为研究对象,对泄漏过程中喷口处稳态气流状态参数变化及其被点燃之后的喷射火火焰形态与辐射热流场预测模型研究进展进行了综述。归类分析了基于理想气体状态方程和Abel-Noble状态方程的高压气体泄漏模型及其适用情况,并对不同浮力控制和动量控制范围的几种喷射火火焰几何尺寸模型进行了概括性总结,同时对不同火焰形态下的点源、多点源、固体以及线源4种热辐射模型进行了汇总,最终提出将3种模型耦合联用以建立适用于不同泄漏条件下喷射火热灾害分析预测方法。分析表明,该分析预测方法具有很好的适用性。     

An experimental and modeling study of heat radiation characteristics of inclined ceiling jet in an airplane cargo compartment

A series of pool fires were carried out in an airplane cargo compartment to investigate the effect of the pressure on the heat radiation flux (HRF) of the inclined ceiling jet fire. During the tests, different static chamber pressures ranging from 50 to 101 kPa were controlled by the air flow in and out; both free fire and inclined ceiling jet fire were conducted with five different heat release rates (HRRs), which were produced by a 17‐cm square porous gas burner using propane as fuel. Vertical flame temperature, thermal plume temperature beneath the inclined ceiling, and HRF to the horizontal floor were measured and analyzed; at the same time, the flame shape was recorded by a video. It was found that the HRF was increased with the HRR, and there was a sudden rise for these fire impinging on the ceiling. The flame radiation fraction had a weak correlation with the environment pressure, while the flame emissivity was increased with the increasing ambient pressure. Besides, on the basis of the assumption that the flame emissivity is equaled in both free flame and the inclined ceiling jet fire, HRF calculated model was established and compared with the experimental results.     

Experimental research on the burning behavior of dragon juniper tree

Tree crown fire is one of the extreme fire behaviors in the wildland‐urban interface. This paper presents an experimental study on the burning behaviors of single and triple dragon juniper trees. The mass loss, flame height, plume temperature, radiation, and fire interaction are measured. It is found that the foliage moisture content and flame mergence dominate the mass consumed percentage (defined as the ratio of the total mass loss to initially total mass), while the tree crown height and flame mergence determine the flame height. The peak mass loss rate is mainly affected by the moisture content and tree species. For triple tree fires, the peak mass loss rate is also affected by the spacing due to the coupled effects of heat feedback enhancement and air entrainment restriction. Results also show that the flame height significantly increases as the spacing decreases. The spacing holds a significant effect on the fire plume temperature distribution and thermal radiation field. Empirical correlations are also developed for the flame height, radial temperature, and radiant heat flux distribution based on physical interpretation of the tree burning behaviors.     

Effect of shielding rates on upward flame spread over extruded polystyrene foam in vertical channel and heat transfer mechanism

Fire hazard of extruded polystyrene (XPS) thermal insulation materials has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of XPS, an experimental study on upward flame spread behavior and heat transfer mechanism of XPS in a vertical channel with different frontal shielding rates was conducted. Maximum temperature at the place 2 cm from XPS surface and at the center of channel first increase and then decrease as the shielding rate rises. The former is higher than the latter. Experimental value of average flame height rises as the shielding rate increases. A model for predicting the flame height is built, and the predicted results are consistent with the experimental results. Moreover, the relation between flame height and pyrolysis height under different shielding rates is obtained. The flame spread rate rises as the shielding rate increases. A prediction model of flame spread rate is established, and its prediction results are more accurate compared with those from previous models. The model also predicts that radiative heat transfer is the dominant heat transfer mode, accounting for 93% of the total heat transfer. This work is beneficial for fire risk assessment and fire safety design of building façade.