无风及侧向风作用下的腔室开口火溢流研究

发布时间：2018-05-05 23:56

本文选题：火溢流 + 腔室火　；参考：《中国科学技术大学》2016年博士论文

【摘要】：开口火溢流是腔室火中一种常见且极为重要的燃烧现象。通风状况在火溢流的形成及蔓延进程中扮演了重要角色。以往研究均主要针对无风下单开口腔室场景,对其他复杂无风及有风场景则鲜有涉及。本文对无风下单开口及双开口以及侧向风作用下的双开口火溢流的形成及燃烧动力学进行了系统理论研究,分析了双开口及侧向风的影响机制；采用燃烧风洞及小尺度腔室火溢流实验台,模拟了不同风速下对称双开口火溢流场景,对其燃烧机理及动力学参数开展了系统研究。研究结果综述如下：对于无风下的单开口腔室火溢流场景,燃料供应速率及腔室温度的升高会造成中性面的降低。基于半峰宽的高斯分布函数揭示了径向温度的轴对称高斯自相似分布规律,实验数据与文献数据较好符合。基于修正Zukoski数和长度因子揭示了无风下单开口火溢流轴向温度与火焰高度的自相似分布规律。在连续火焰区、间歇火焰区及浮力羽流区,火溢流的轴向温度自相似分布函数具有与经典羽流一致的幂指数。随着过余热释放速率增加,火溢流逐渐由墙面火向轴对称火焰转变,在墙面火焰区火焰高度自相似分布函数的幂指数与经典羽流不同,壁面附近空气卷吸受限可能是主要原因。无风条件下,相比于单开口情形,双开口的存在会使腔室的中性面升高,并对腔室火温度产生影响。基于理论推导获得了无风下非对称双开口火溢流的中性面高度模型,与文献中数据符合较好。侧向风的加入,会因补充氧气促进燃烧,也可冷却可燃物,这两种效应会相互竞争,从而对腔室燃烧强度和室内温度产生影响。理论推导表明,侧向风对对称双开口的腔室火溢流压差分布产生三种影响,即直接在顺风及逆风沿的腔室开口施加风压：造成静压变化：造成流体静压变化。侧向风的作用还会造成小尺度对称双开口腔室火溢流顺风沿和逆风沿中性面升高及降低,并影响火溢流的流态及流动方向。以上推导的结论均与实验数据一致。不同侧向风风速下的实验数据表明,采用半峰宽(FWHM)作为归一化变量的无量纲高斯函数可以较好地拟合不同风速下的径向温度数据,不会因不同风速造成的轴线轨迹弯曲而变化。侧向风作用会使火溢流轴线轨迹形成初始阶段的脱离壁面区域和随后的附着壁面区域：半峰宽(FWHM)沿高度方向上呈弱线性分布。侧向风风速1.5 m/s及3 m/s的实验数据表明,耦合侧向风的无量纲模型及长度因子可以较好地对不同侧向风风速、开口尺寸和内部燃烧强度下的火溢流轴向温度及壁面总热通量进行拟合。在连续火焰区、间歇火焰区及浮力羽流区,火溢流轴向温度自相似分布函数具有与经典羽流一致的幂指数：风速增加会使得二个火焰分区之间的转化加快,空气卷吸增强是主要原因。侧向风作用造成的中性面高度下降会增强火溢流的近场及远场空气卷吸；外立面的空气卷吸受限也会对火溢流的温度分布及轴线轨迹产生显著的影响。不同风速下的数据表明,侧向风的作用会对壁面总热通量及温度产生两个相互竞争的作用,使其随着风速增加出现非线性变化趋势。
[Abstract]:Open fire overflow is a common and extremely important combustion phenomenon in the chamber fire. Ventilation has played an important role in the formation and spread of the fire overflow. Previous studies were mainly aimed at the single opening of the oral chamber scene without wind, and rarely involved in other complicated and windless scenes. The formation of double opening fire overflow and combustion dynamics under side wind are systematically studied, and the influence mechanism of double opening and lateral wind is analyzed. The flow field of symmetrical double opening under different wind speeds is simulated by combustion wind tunnel and small scale chamber fire overflow test platform, and its combustion mechanism and dynamic parameters are carried out. The research results are summarized as follows: for a single open oral chamber fire overflow scene without wind, the fuel supply rate and the increase of the chamber temperature will result in the reduction of the neutral surface. The Gauss distribution function based on the half peak width reveals the axisymmetric Gauss self similarity distribution of the radial temperature, and the experimental data are in good agreement with the literature data. Based on the modified Zukoski number and the length factor, the self similar distribution of the axial temperature and the flame height of a single open fire overflow is revealed. In the continuous flame region, the intermittent flame region and the buoyancy plume, the self similar distribution function of the axial temperature of the fire overflow has the power exponent consistent with the classical plume. With the increase of the rate of excess heat release, The fire overflow gradually changes from the wall fire to the axisymmetric flame. The power exponent of the self similar distribution function of the flame height in the wall flame area is different from that of the classical plume. The air entrainment near the wall may be the main reason. Under the condition of no wind, the double opening will increase the neutral surface of the chamber and the chamber fire temperature. Based on the theoretical deduction, the neutral surface height model of unsymmetrical double opening fire overflow is obtained, which is in good agreement with the data in the literature. The addition of the side wind will increase the combustion and can cool the combustibles. These two effects will compete with each other, thus influencing the chamber combustion strength and indoor temperature. The derivation shows that the lateral wind has three effects on the distribution of the pressure difference distribution in the chamber with symmetrical double opening, that is, the wind pressure is applied directly to the opening of the chamber with the wind and the opposite wind, which causes the static pressure change: the hydrostatic pressure changes. The lateral wind will also cause the small scale symmetrical double opening chamber fire overflow along the wind and the counter wind to rise along the neutral surface. The above conclusions are all consistent with the experimental data. The experimental data under different lateral wind speeds show that the dimensionless Gauss function using half peak width (FWHM) as a normalized variable can well fit the radial temperature data under different wind speeds and will not be caused by different wind speeds. The axis trajectory of the axis changes. The lateral wind can cause the fire overflow axis to form the initial stage of the separation from the wall area and the subsequent attachment wall area: the half peak width (FWHM) is a weak linear distribution along the direction of height. The experimental data of 1.5 m/s and 3 m/s for the lateral wind wind speed show that the dimensionless model and length factor of the wind in the coupling side In the continuous flame region, the intermittent flame area and the buoyancy plume region, the self similar distribution function of the fire overflow axial temperature is consistent with the classical plume in the continuous flame region, the intermittent flame area and the buoyancy plume region. The increase of wind speed will make the wind speed increase two. The main reason for the conversion between the flame zones is that the air entrainment is the main reason. The decrease of the neutral surface caused by the lateral wind effect will enhance the near and far field air entrainment of the fire overflow; the air entrainment limitation of the outer surface will also have a significant effect on the temperature distribution and axis trajectory of the fire overflow. The effect of wind on the total heat flux and temperature of the wall has two competing effects, making it nonlinear trend with the increase of wind speed.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X932

【相似文献】