油池火火焰颈部特征及发展区温度分布研究

发布时间：2018-03-15 20:43

本文选题：火焰颈部收缩深度(速度)　切入点：颈部上升高度(速度)　出处：《中国科学技术大学》2015年硕士论文　论文类型：学位论文

【摘要】：火焰颈部收缩行为在扩散油池火底部是一个基木的行为,是由于密度差导致空气卷吸形成的,同时这也是火焰周期性脉动的原因。然而,火焰颈部收缩动态特性的演化的测量及他们与火焰不稳定机制的关系在前人的研究中暂时缺乏。本文定量分析了油池尺寸为0.04-0.25m的火焰颈部特性及不稳定机制。基于对火焰帧序列图片的直接测量,火焰宏观参数颈部收缩最大深度(Dmax),颈部收缩平均速度(Unecking-in),颈部上升最大高度(Hmax),颈部上升平均速度(Uuprising)及涡脉动频率和涡生长时间在本文中都被定量出来了。基于测量的结果研究了这些参数随油池尺寸及边缘高度的演化规律。定义了三种火焰不稳定机制：小尺度的Rayleigh-Taylor(R-T)不稳定,扩展R-T不稳定及puffing.研究发现随着油池尺寸及边缘高度的增大主控的不稳定机制从R-T不稳定转化成puffing.大尺度的涡结构的抽运能力(可以通过(Dmax,Hmax,Unecking.,Uuprising的值来定量)和扩展R-T不稳定机制的频率有一定的关系。扩展R-T不稳定机制的频率比puffing机制的频率要高。Puffing机制的频率随着边缘高度(油池上边沿与液面的距离)的增大略有增大随着油池直径的增大而减小,和经典的关系式(f～D-1/2,或者无量纲的St～Fr-1/2)一致。同时扩展R-T不稳定机制的频率(f)满足关系式fR-T.extended～(lg2/Q)1/3。扩展R-T不稳定机制的生长时间(τ)随着油盘直径的增大而增大并且比puffing机制的生长时间小,puffing机制的生长时间满足经典关系式τ～D1/2。同时本文对于火焰颈部收缩特征在不同的低大气压强下也做了研究。分析了三种不稳定机制(小尺度R-T不稳定,扩展R-T不稳定及puffing)随大气压强,油盘尺寸的演化。随着油池直径或者大气压强的增大,主控频率从扩展R-T不稳定转换成puffing.定量出了不同大气压强下油池火焰颈部收缩宏观尺度,并且探讨了颈部收缩宏观参数随大气压强的变化。其中无量纲颈部收缩最大深度Dmax和颈部收缩水平速度Unecking一in随大气压强的变化很小；无量纲颈部上升最大高度Hmax和颈部上升竖直速度Uuprising随着大气压强的增大而减小；无量纲颈部收缩最大深度Dmax和无量纲颈部上升最大高度Hmax的比值及颈部收缩水平速度Unecking-in和颈部上升竖直速度Uuprising的比值都随着大气压强的增大而增大。puffing机制的频率随着大气压强增大而略有增大,随着边缘高度的增大而增大；扩展不稳定机制频率随着压强及边缘高度没有明显的趋势。除了对油池火焰颈部收缩特征的研究,本文对油池火焰发展区温度也做了研究。经典的火羽流模型中(连续火焰区,间隙火焰区及浮力羽流区)没有包括燃料液面上的发展区温度分布。前人的文章对发展区温度分布的实验数据也很少。那么本文首先定量出了不同尺寸的油池火焰的温度分布。研究发现对于不同的油池尺寸火焰发展区温度分布及到达最高温度的位置不同。温度上升行为的物理机制是未燃烧的燃料与空气的逐渐混合比下降。那么,基于这种物理机制,本文假设了一种Beta型的概率分布函数并且利用混合分数的方法推导出了预测发展区中心线温度的方法。发现这种预测温度的方法得到的结果与实验数据吻合很好。
[Abstract]:Flame neck shrinkage behavior is a basic behavior in the diffusion at the bottom of the pool fire, is due to density difference leads to the formation of air entrainment, which is also the reason for flame pulsation. However, measuring the evolution of dynamic characteristics of the flame neck shrinkage and their relationship with the flame instability mechanism temporarily lacking in previous studies in this paper. Quantitative analysis of oil pool size for the flame characteristic of 0.04-0.25m and cervical instability mechanism. Direct measurement of flame image frame sequence based on the macro parameters of cervical flame maximum depth (Dmax), systolic contraction of the average speed of the neck (Unecking-in), maximum height (Hmax), the neck neck increased the average speed (Uuprising) and the vortex pulsation frequency and vortex growth time were quantitatively out in this paper. Based on the measuring results of these parameters with the evolution of oil pool size and edge height are defined. Three kinds of flame instability mechanism: the small scale Rayleigh-Taylor (R-T) is not stable, unstable and extended R-T puffing. study found that the pumping ability of vortex structure instability mechanism of oil pool size and edge height increases the master from the R-T instability into the large scale of the puffing. (by (Dmax, Hmax, Unecking., the value of Uuprising in quantitative) have a certain relationship and extended R-T instability mechanism of frequency. The extended R-T instability mechanism more frequently than the puffing.Puffing mechanism mechanism of frequency with edge height (above the oil pool along with the increase of liquid surface distance) increased slightly decreases with increasing the diameter of the oil pool and, the classic formula (F ~ D-1/2, St ~ Fr-1/2 or dimensionless). At the same time extended R-T frequency instability mechanism (f) satisfy the relation fR-T.extended ~ (lg2/Q) 1/3. extended R-T instability growth mechanism Between (tau) increases with increasing diameter of the oil pan and the specific growth time of puffing mechanism, puffing mechanism to meet the growing time of classical formula tau ~ D1/2.
At the same time the flame neck shrinkage characteristics at low atmospheric pressure under different were also studied. Analyzed three kinds of instability mechanism (small scale R-T is not stable, unstable and extended R-T puffing) with the atmospheric pressure, the evolution of Pan size. With the pool diameter or the atmospheric pressure increases, the main control from the frequency of extended R-T instability into puffing. quantitatively different atmospheric pressure oil pool fire neck shrinkage macro scale, and discusses the change of macro parameters with the neck contraction of the atmospheric pressure. The dimensionless maximum depth Dmax and neck shrinkage shrinkage neck Unecking in horizontal velocity change with the atmospheric pressure is very small; the dimensionless maximum height of the neck and neck Hmax Uuprising vertical velocity decreases with the rise of the atmospheric pressure increases; the dimensionless maximum depth Dmax and neck shrinkage dimensionless neck maximum height ratio of Hmax The ratio of value and systolic velocity Unecking-in and neck neck level rise speed of Uuprising with vertical pressure increases with the increase of.Puffing mechanism and frequency slightly increase with atmospheric pressure increases, and increases with the increase of edge height; extended frequency instability mechanism with pressure and edge height had no obvious trend.
In addition to the study of pool fire neck shrinkage characteristics of the oil tank, the flame development zone temperature were also studied. Fire plume model (Continuous flame zone, gap flame zone and plume zone) did not include the development of the temperature distribution on the surface of the fuel. The previous article on the development of the temperature distribution the experimental data are few. So this paper quantitatively the temperature distribution of pool fire in different sizes. The study found that different for different oil pool size of flame temperature distribution and development area at the highest temperature. The physical mechanism of temperature rising behavior is not burning the fuel and air mixing ratio decreased gradually. So, the physical mechanism based on this assumption, the probability distribution function of a Beta type and using the method of mixture fraction derived from the method of temperature prediction line development zone center. The prediction of temperature The results obtained by the method are in good agreement with the experimental data.

【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE88

【共引文献】