超声速燃烧中可压缩湍流燃烧模型研究

发布时间：2018-04-23 04:14

本文选题：超声速燃烧冲压发动机 + 大涡模拟　；参考：《中国科学技术大学》2015年博士论文

【摘要】：超声速燃烧冲压发动机因为能够实现高超声速飞行(5Ma15)成为近年来的研究热点。由于超声速燃烧实验测量手段复杂、实验设备昂贵,计算流体力学方法成为研究超声速燃烧冲压发动机的重要手段。超燃冲压发动机燃烧室内存在复杂的激波/边界层、激波/火焰的相互作用以及自点火、局部熄火、再点燃、火焰驻定等非定常的燃烧过程,发展超声速燃烧模型和数值方法对研究超燃冲压发动机内的流动和燃烧特征非常重要。本文主要开展以下几个方面的研究： (1)发展基于化学热力学建表的可压缩湍流燃烧模型；(2)基于发展的可压缩火焰面进度变量方法对超声速支板射流DLR燃烧室的燃烧特征分别开展RANS和LES数值研究；(3)采用LES方法结合可压缩修正的自点火燃烧模型分别研究高焓值超声速横侧射流Gamba燃烧室的混合特性和燃烧特性。超声速流场中的可压缩效应如压缩／膨胀过程产生的压力、密度和温度的变化,对化学反应过程产生重要影响。因此,将低马赫数下的化学热力学建表方法应用到超声速可压缩流时需要考虑高速流体的可压缩性。本文对化学热力学建表模型的可压缩修正方法进行了深入研究。本文引入了温度和压力修正方法。在可压缩化学热力学建表方法中,通过直接求解能量方程得到温度值,可以耦合部分可压缩性影响；通过分析不同压力下层流化学热力学数据表,给出反应进度变量源项的压力修正系数,对反应进度变量源项进行压力修正。此方法的优点是能够在不增加化学热力学数据表的大小的基础上考虑流场的压力变化,并可以推广应用到采用反应进度变量建表的模型中；超声速横侧射流燃烧算例中,在以上温度与压力修正的基础上,提出了修正自点火模型中初始温度的方法,考虑燃料射流近场由于压缩／膨胀引起温度的不均匀分布。采用可压缩火焰面进度变量方法对超声速支板射流DLR燃烧室三维流场和燃烧场开展RANS和LES数值研究。相比与RANS方法,LES方法得到的冷态场中压力分布、波系分布、速度分布以及燃烧场中波系分布、速度分布、温度分布结果均与实验值符合更好。LES方法可以预测超声速中的大尺度湍流拟序结构以及非定常的流动及燃烧过程,能够捕捉激波与边界层的相互作用、湍流混合、火焰驻定以及熄火再燃等问题；LES结果表明,钝体两侧剪切层内形成了熄火再燃的不稳定火焰,在燃烧室中心回流泡内形成了稳定的富燃部分预混火焰；在LES框架下,分别采用的ε与β两种概率密度分布对反应进度封闭。对比结果发现,假定概率密度的β分布计算结果与实验符合较好,假定概率密度的δ分布没有考虑反应进度变量的亚格子脉动,得到平均温度偏高。因此,反应进度变量的亚格子脉动对预测超声速燃烧非常重要。采用LES方法研究了超声速横侧射流Gamba燃烧室内的大尺度序结构和混合特性。采用混合分数概率密度函数分析燃料射流喷口上游回流区、射流近场以及射流远场的混合特征,并探讨射流动量通量比对流场结构、射流穿透深度、标量分布以及混合效率的影响。结果表明,低射流动量通量比时,反向旋转涡对CVP结构与壁面边界层相互作用更强烈,燃料的质量分数沿着横向方向扩散的更快,混合效率更高。考虑到超声速来流温度高于燃料的自点火温度,采用修正的自点火燃烧模型研究了Gamba燃烧室燃烧场内的流场结构、射流穿透深度、涡结构以及燃烧特征。由于反应放热,燃烧场中,反向旋转涡对CVP与尾迹反向旋转涡对TCVP结构变大、射流穿透深度提高。计算得到燃烧场三个燃烧反应区域：射流入口上游的点火点、射流剪切层以及近壁面射流尾迹区。近壁面射流尾迹区火焰稳定主要由尾迹反向旋转涡对TCVP结构控制。
[Abstract]:Supersonic combustion ramjet has become a hot spot in recent years because of its ability to achieve hypersonic flight (5Ma15). Due to the complexity of the experimental measurement methods and the expensive experimental equipment, computational fluid dynamics (CFD) has become an important part of the study of the supersonic combustion ramjet engine. Shock / boundary layer, shock / flame interaction, self ignition, local extinguishing, rekindling, flame stationing and other unsteady combustion processes, developing supersonic combustion model and numerical method are very important to study the flow and combustion characteristics in the scramjet. This paper is to carry out the following aspects: (1) development basis The compressible turbulent combustion model was built by chemical thermodynamics; (2) RANS and LES numerical studies were carried out on the combustion characteristics of the supersonic jet DLR combustor based on the developed compressible flame surface progress variable method. (3) the high enthalpy supersonic lateral side was studied by the LES method and the self point fire combustion model combined with the compressible modified self point fire model respectively. The mixing and combustion characteristics of the jet Gamba combustor. The compressibility effect in the supersonic flow field, such as the pressure, density and temperature change produced by the compression / expansion process, has an important influence on the chemical reaction process. Therefore, the application of the chemical thermodynamics method under the low Maher number to the supersonic compressible flow needs to be considered at high speed. The compressibility of fluid is studied in this paper. In this paper, the compressible correction method of the chemical thermodynamics model is deeply studied. In this paper, the temperature and pressure correction method is introduced. In the compressing chemical thermodynamics table method, the temperature value can be obtained by directly solving the energy equation, and the effect of the compressibility of the coupling part can be coupled; the different pressure is analyzed by the analysis of the pressure. The lower layer flow chemical thermodynamics data table, the pressure correction coefficient of the reaction progress variable source term is given, the pressure correction of the reaction progress variable source term is corrected. The advantage of this method is that the pressure change of the flow field can be considered on the basis of the size of the chemical thermodynamics data sheet, and can be popularized and applied to the construction of the table with the reaction progress variable. In the model of the supersonic lateral jet combustion calculation, on the basis of the above temperature and pressure correction, a method of correcting the initial temperature in the self ignition model is proposed, considering the inhomogeneous distribution of the temperature caused by the compression / expansion of the fuel jet in the near field. The method of the compressible flame surface progress variable method is used for the DLR combustion of the supersonic ramp jet. RANS and LES numerical studies are carried out in the three-dimensional flow field and combustion field of the burning chamber. Compared with the RANS method, the pressure distribution in the cold state, the distribution of wave system, the distribution of velocity and the distribution of wave system in the combustion field, the velocity distribution, the distribution of velocity and the temperature distribution are all in accordance with the experimental values by the LES method. The.LES square method can predict the large scale turbulent pseudo sequence in the supersonic velocity. The structure and unsteady flow and combustion process can capture the interaction between the shock wave and the boundary layer, the mixing of the turbulent flow, the stationary flame and the reburning of the flame. The LES results show that the unsteady flame of the flameout reburning is formed in the shear layer on both sides of the blunt body, and a stable combustion part of the premixed flame is formed in the central reflux bubble of the combustor. Under the LES framework, the two probability density distributions of epsilon and beta are closed to the reaction schedule. The results show that the calculated results of the beta distribution of the probability density are in good agreement with the experiment. It is assumed that the delta distribution of the probability density does not take into account the subgrid pulsation of the reaction progress variable, and the average temperature is high. Therefore, the reaction progress variable is obtained. The subgrid pulsation is very important for the prediction of supersonic combustion. The large scale order structure and mixing characteristics of the supersonic lateral jet Gamba combustion chamber are studied by using the LES method. The mixed fraction probability density function is used to analyze the mixing characteristics of the upstream reflux region, the near field of the jet and the far field of the jet, and to discuss the flow of the jet flow. The effect of the volume ratio on the flow field structure, the penetration depth of the jet, the distribution of the scalar and the mixing efficiency. The results show that the reverse rotating vortex has a stronger interaction between the CVP structure and the wall boundary layer when the flux ratio is low. The mass fraction of the fuel is faster in the transverse direction and the mixing efficiency is higher. Considering the supersonic flow temperature is higher than that of the flow rate, the temperature of the flow is higher than that of the flow rate. The self ignition temperature of the fuel and the modified self ignition combustion model are used to study the structure of the flow field in the combustion chamber of the Gamba combustion chamber, the penetration depth of the jet, the structure of the vortex and the characteristics of the combustion. As the reaction exothermic, the reverse rotating vortices of the combustion field increase the structure of the TCVP structure with the reverse rotating vortex of the CVP and the wake, and the penetration depth of the jet is increased. The combustion of the combustion is calculated. The three combustion reaction regions: the ignition point upstream of the jet inlet, the shear layer of the jet and the wake region of the near wall jet. The stability of the wake region in the near wall jet is mainly controlled by the reverse rotating vortex of the wake to the TCVP structure.

【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】：2015
【分类号】：TK16

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