直到耗散尺度的湍流与复杂化学相互作用数值模拟研究

发布时间：2018-06-18 17:19

本文选题：火灾 + 一维湍流模型　；参考：《中国科学技术大学》2013年博士论文

【摘要】：实际火灾是湍流燃烧过程,而在湍流燃烧中湍流流动与复杂化学是时空多尺度耦合作用的。研究湍流与复杂化学的相互作用是一项既有挑战也十分有意义的课题。湍流的空间尺度可以分为含能尺度、惯性子区尺度和耗散尺度三个层次。湍流涡旋从最小的耗散尺度开始就与火焰有着强烈的相互作用。数值模拟研究湍流与复杂化学的相互作用需要解决耦合详细化学反应机理的耗散尺度湍流反应流模拟,和海量模拟结果诊断分析的两个难题。本文采用一维湍流模型(one-dimensional turbulence, ODT)和化学反应爆炸模式分析方法(chemical explosive mode analysis, CEMA)解决了这两个难题,建立了ODT+CEMA分析湍流与复杂化学相互作用的数值分析平台,并对典型灭火剂与氢气射流火焰的相互作用进行了数值模拟和深入分析。复杂化学研究中,详细化学反应机理的分析及简化对实现湍流耦合复杂化学的数值模拟十分重要。本文中采用关系图法对典型碳氢燃料反应机理进行了简化研究。不但研究了在保持一定计算精度情况下简化机理能达到的最小规模,还深入分析了方法参数对简化结果的影响,并且引入强关系组分群的概念,分析了复杂化学反应机理中强关系组分群的聚集、分布情况。为了加快反应机理的计算,本文还做了利用图形显卡并行计算求解大型化学反应机理的研究,在大型机理情况下计算加速效果明显。一维湍流模型ODT,可以实现耦合复杂化学的耗散尺度湍流反应流模拟。本文介绍了ODT模型的计算框架、湍流模拟机制和数值求解方法。并用此方法模拟分析了氢气射流火焰,以及添加典型灭火剂后的射流火焰基本特性。高精度的湍流反应流模拟会产生海量的计算数据,传统采用典型系统参数如温度、关键组分的浓度,甚至一阶导数的分析方法已经不适合处理如此庞大、精细的计算结果。化学反应爆炸模式分析方法是一种分析湍流反应流局部系统特征值的方法。本文系统介绍了化学反应爆炸模式分析方法的数学基础和基于ODT模拟数据的湍流反应流信息分析方法。通过对添加灭火剂的氢气空气预混热自燃模型的化学反应爆炸模式分析发现,系统反应进行最剧烈的时候也是最大正特征值发生明显变化的时刻。添加了灭火剂后,热自燃时间不但明显推迟,其反应进程和最大正特征值的突变性更加明显。化学反应爆炸模式分析可以直观的观察到湍流反应流局部系统状态的变化,对诊断湍流火焰中的热自燃、熄火、重燃等行为十分有效。局部Damkohler数是控制火焰结构,研究湍流与复杂化学相互作用的重要参数。在本文分析中重新定义了Damkohler数。通过分析湍流火焰在新Da数空间的散点分布发现：新定义的Da数是判定局部熄火的良好标准,而灭火剂的作用途径主要是通过增大局部反应系统的热自燃时间,进而减小Da数,增加熄火概率。通过分析,本文还解释了Re数增加时灭火剂灭火效果增加的原因。研究结果明确指出了主要组分和主要基元反应在射流火焰中的作用区域,以及在火焰抑制效果不同时,火焰中心区域主要作用组分和基元反应的差异。本文的主要创新点和贡献在于：为研究湍流与复杂化学相互作用,建立了ODT+CEMA的数值分析平台,提供了一种分析湍流与复杂化学相互作用的新方法。
[Abstract]:The real fire is a turbulent combustion process , and the turbulent flow and complex chemistry in turbulent combustion are both time - space and multi - scale coupling . The research on the interaction between turbulence and complex chemistry is an important subject . The spatial scale of turbulence can be divided into three levels including energy scale , inertial sub - zone scale and dissipation scale . The turbulent vortex has strong interaction with the flame from the minimum dissipation scale .

Numerical simulation of the interaction between turbulent and complex chemistry needs to solve the two difficult problems of the dissipation scale turbulent flow simulation of coupled detailed chemical reaction mechanism and the diagnosis and analysis of massive simulation results . The two problems are solved by using one - dimensional turbulent model ( odt ) and chemical reaction explosion pattern analysis ( CEMA ) . The numerical analysis platform for analyzing the interaction of turbulence and complex chemical interaction is established . The interaction between typical fire extinguishing agent and hydrogen jet flame is simulated and analyzed in depth .

In the study of complex chemistry , the analysis and simplification of the mechanism of chemical reaction are very important to realize the numerical simulation of the complex chemistry of turbulent coupling .

The dissipation scale turbulent flow simulation of coupled complex chemistry can be realized by one - dimensional turbulent model . The calculation framework , turbulence simulation mechanism and numerical solution method of the odt model are introduced in this paper , and the basic characteristics of the jet flame after the typical fire extinguishing agent are added are simulated by this method .

High - precision turbulent reaction flow simulation results in massive computational data . Traditional system parameters such as temperature , concentration of key components , and even first derivative analysis method are not suitable to deal with such a large and fine calculation result . The chemical reaction explosion pattern analysis method is a method for analyzing the characteristic value of local system of turbulent flow reaction flow . The system introduces the mathematical basis of chemical reaction explosion pattern analysis method and the turbulence reaction flow information analysis method based on the odt simulation data .

By the chemical reaction explosion mode analysis of the hydrogen air pre - mixing self - ignition model to add the fire extinguishing agent , it is found that the most violent time is the time when the maximum positive characteristic value changes obviously . After the fire extinguishing agent is added , the heat self - ignition time is obviously delayed , and the reaction progress and the maximum positive characteristic value are more obvious . The chemical reaction explosion mode analysis can visually observe the change of the local system state of the turbulent flow reaction flow , and is very effective for diagnosing the heat self - ignition , extinguishing , reburning and the like in the turbulent flame .

The local Damkohler number is an important parameter for controlling the flame structure and studying the interaction between turbulence and complex chemical . In this paper , we redefine the Damkohler number . By analyzing the distribution of turbulent flame in the new Da number space , it is found that the Da number newly defined is a good standard for judging local extinguishment , and the action way of the fire extinguishing agent is mainly by increasing the heat self - ignition time of the local reaction system , thus reducing the Da number and increasing the extinction probability .

Through the analysis , this paper also explains the reason for the increase of the extinguishing effect of the fire extinguishing agent when Re number is increased . The results clearly show that the main components and main elements react in the jet flame , and the difference of the main components and elementary reactions in the central zone of the flame is not the same as the flame suppression effect .

The main innovation points and contributions of this paper are : To study the interaction between turbulence and complex chemistry , a numerical analysis platform for the odt + CEMA is established , and a new method for analyzing the interaction between turbulence and complex chemistry is provided .
【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】：2013
【分类号】：O643.21;TU998.1

【参考文献】