大涡模拟航空发动机加力燃烧室内部流场

为研究航空发动机加力燃烧室内部气流的流动情况,基于LES计算方法,选用动态亚网格湍流模型对燃烧室内非反应流场进行数值研究。模拟结果显示:在中心锥后侧有较大回流区;在空心叶片尾部存在稳定回流区,表明大涡模拟动态亚网格模型能够模拟出加力燃烧室筒体内尺寸较小的涡团及涡团的掺混耗散过程,可较好地展现加力燃烧室实际的流动过程和特性。     

粉煤气化炉喷嘴旋流数对炉内流场及燃烧特性的影响

对带旋流单喷嘴粉煤加压气化炉内多相燃烧流场,建立二维旋流对称模型进行数值模拟。计算采用涡耗散概念模型,同时考虑体积反应和焦炭表面反应,模拟多机理的湍流燃烧。通过改变喷嘴内部旋流数进行平行模拟,研究不同旋流数下炉内流场的回流分布特性以及火焰的形态和分布等燃烧特性。结果表明:带有旋流喷嘴的气化炉,炉内流场分布主要由中心回流区和外回流区的旋流涡构成;旋流数增大导致轴向速度衰减加快,延长了粉煤颗粒在炉内停留时间,但旋流过大会导致颗粒在炉顶聚集形成"死区";旋流数S≤1.2时,火焰为锥子状,炉内整体高温不利于气化反应;旋流数S≥1.6时,炉内高温区上移至炉顶,火焰呈扁平花瓣状,扩散角过大容易形成回火;通过拟合高斯曲线得到本气化炉最佳旋流数为1.4。     

以天然气为燃料的燃气轮机燃烧室燃烧场数值模拟

某燃气轮机以天然气为燃料,对其燃烧室燃烧流场进行数值模拟,得到典型工况的速度场、温度场、CO2分布,总结了燃烧室出口温度不均匀度、燃烧效率的变化规律。结果表明:旋流器的导向作用明显,在火焰筒头部出现了明显的回流区,有利于火焰稳定;随着工况升高,燃烧室出口平均速度增大、CO2质量分数增大,燃烧效率提高;燃烧室出口温度分布均匀,掺混孔的掺混效果较好。     

凹槽火焰稳定器前缘结构对煤油超声速燃烧的影响

采用离散液滴模型、概率密度函数紊流燃烧模型和两方程紊流模型数值,模拟了双模态冲压发动机燃烧室内不同前壁面结构凹槽的超声速燃烧火焰稳定特性。在相同的计算条件下,数值分析结果表明:与具有正规凹槽结构的燃烧室相比,具有斜面凹槽结构的燃烧室:壁面静压分布更加合理;其内涡量比较强;燃烧室出口总压恢复系数和燃烧室效率都比较大。因而认为斜面凹槽火焰稳定器提高了混合和燃烧,优于正规凹槽火焰稳定器。     

主燃孔方案对回流燃烧室流动影响的数值研究

为探究主燃孔开孔方案对辅助动力装置回流燃烧室流动特性的影响,开展5种主燃孔开孔方案的矩形回流燃烧室冷态流场数值模拟研究,数值模拟方法通过粒子图像测速试验数据进行了有效性验证。结果表明：燃烧室主燃区流场形成了大尺度双涡流动结构,有利于火焰稳定。外环主燃孔射流穿透深度明显大于内环主燃孔射流,因此对流场影响更大。外环主燃孔数目越多,孔径越小,主燃区沿轴向和展向的尺寸都变大。主燃孔排列方式对主燃区流场结构影响很小,但对中间区流场影响显著。     

某型燃机燃烧室的数值模拟

燃料喷嘴双级径向旋流器在燃烧室内形成稳定的回流漩涡结构,有助于燃烧室火焰稳定和提高燃烧效率。文中建立了计算模型,利用CFX软件进行燃烧室的燃烧模拟,研究了燃烧室中流场分布、NO含量分布、温度场分布、燃料分布。模拟计算表明,此燃烧室具有较好的气动特性、稳燃性能与冷却性能,能够在额定工况下长时间稳定工作。     

不同头部间距下三头部燃烧室点火过程研究

为了探讨不同头部间距对某型航空发动机燃烧室点火过程中火焰传播特性的影响,建立三头部燃烧室燃烧试验系统,开展流动与点火过程中火焰传播特性、头部间距对周向点火过程影响规律的实验研究.研究表明:燃烧室的周向点火过程具有阶段性,在初始火焰发展阶段,火焰首先顺着流线方向传递,待燃烧强度增大到一定值时,火焰才开始向其他区域延伸;在相同工况下,头部间距较小时,相邻旋流器之间的局部回流区相互影响增大,油气掺混效果增强;随头部间距增加,流动因素对火焰传播的作用减小.     

不同头部间距下三头部燃烧室点火过程研究

为了探讨不同头部间距对某型航空发动机燃烧室点火过程中火焰传播特性的影响,建立三头部燃烧室燃烧试验系统,开展流动与点火过程中火焰传播特性、头部间距对周向点火过程影响规律的实验研究.研究表明:燃烧室的周向点火过程具有阶段性,在初始火焰发展阶段,火焰首先顺着流线方向传递,待燃烧强度增大到一定值时,火焰才开始向其他区域延伸;在相同工况下,头部间距较小时,相邻旋流器之间的局部回流区相互影响增大,油气掺混效果增强;随头部间距增加,流动因素对火焰传播的作用减小.     

燃烧室形状对缸内直喷CNG发动机燃烧特性影响的数值模拟

为了研究燃烧室形状对于缸内直喷CNG发动机燃烧特性的影响,以6105型CNG发动机为研究对象,利用AVL-FIRE软件建立该型发动机模型,将三类典型的燃烧室(缩口型,直口型,敞口型)进行对比。分析缸内的湍动能分布、速度场、温度场等数据后得出:直口型燃烧室缸具有较强的湍流运动,涡团与CH4的浓度分布有利于稳定火核的形成,提高燃烧速度,动力性较好。     

燃烧室结构对天然气转子发动机燃烧过程的影响

以一台由端面进气汽油转子发动机改装而来的预混天然气转子发动机为研究对象,在FLUENT软件的基础上通过编程实现转子发动机三维网格的偏心运动,并选择合适的湍流模型、燃烧模型以及详细的CHEMKIN化学反应机理,建立基于化学反应动力学的端面进气天然气转子发动机三维动态数值模拟模型。通过与试验数据进行对比和分析,验证模型的可靠性。在此基础上,研究燃烧室结构对端面进气天然气转子发动机的缸内流场、温度场和中间产物浓度场的影响。结果表明,当燃烧室凹坑布置于转子曲面长度方向的前端和转子曲面宽度方向的中心时,燃烧过程同时利用了燃烧室后部的滚流以及燃烧室中部高速流区对火焰的加速作用,缸内整体燃烧速率最大。同时,其缸内压力最大以及中间产物OH的生成量也最大,其压力峰值比中置凹坑燃烧室提高了19.9%,但其NO质量分数仍在0.5%以内。     

Numerical simulation of dump combustor with auxiliary fuel injection

Solutions of the steady, two-dimensional Navier-Stokes, thermal energy, radiation flux, and species conservation equations have been computed for a dump combustor geometry with downstream constriction. The equations are solved in the conservative finite-difference form on a nonuniform rectilinear grid of sufficient resolution to capture the momentum/thermal boundary layers accurately. The numerical procedure, SIMPLEST, which is a variation of SIMPLE, is used to ensure more rapid convergence. A κ−ε model is incorporated for the enclosure of turbulence with a wall function. The combustion model, ESCRS (extended simple chemically-reacting system) with eddy break-up model for the reaction rates of species conservation equation or energy equation is also used. For the good destruction of hazardous waste, it is effective that the waste is injected in the recirculation zone of high temperature with the condition not disturbing the combustion cavity. Excess oxygen from a lean core flame can be effectively utilized for waste destruction with the hydrocarbon waste injection as fuel-rich condition. The core flame has a significant impact on the structure of recirculation cell, in some cases completely changing the nature of the flow within the cavity. The optimum velocity of waste injection exists for the highest temperature at the recirculation zone. A premixed flame type for the auxiliary fuel is good for high temperature and long residence time to be large cavity in the recirculation zone.     

Combustion and heat transfer characteristics inside the combustion chamber of a wood pellet boiler

A grate-firing boiler was developed for wood pellet fuel, and then its combustion characteristics were tested. The flame was stretched to the exit of the combustion chamber, implying insufficient space for complete combustion. As a first step to resolve this problem, a numerical simulation was conducted for the combustion chamber. Turbulent and chemically reacting flow was considered by implementing a homogeneous reaction model. Flow field from the simulation showed strong recirculation flow at the upstream corner of the chamber, along which the flame was stretched to the exit. Based on these results, we suggest possible modification of the combustion chamber to improve combustion characteristics, such as relocating its exit or installing internals like guide vanes.     

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry(PIV)system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.     

基于CFD的氢气／空气当量比对微尺度燃烧室燃烧特性影响的分析

以美国麻省理工学院（MIT）研制的硅基六晶片微燃烧室为研究对象,提出利用二维CFD（计算流体动力学）数值模拟的方法,研究在保持微尺度燃烧室进口氢气／空气流量不变的情况下,改变氢气／空气当量比对燃烧室燃烧特性的影响。整个模拟计算主要包括氢气／空气的流动路径、微燃烧室的内部区域以及整个燃烧室的墙壁面;同时在计算过程中我们考虑了氢气／空气的流体动力学特性、传热学特性和详细的基元反应机理。结果表明,利用二维CFD数值模拟的方法研究微尺度燃烧室燃烧特性可行,与国外实际测量结果较为相似,为今后微型燃气轮机燃烧室的研制及改进提供了一定的参考依据。     

Idealized gas turbine combustor for performance research and validation of large eddy simulations

This paper details the design of a premixed, swirl-stabilized combustor that was designed and built for the express purpose of obtaining validation-quality data for the development of large eddy simulations (LES) of gas turbine combustors. The combustor features nonambiguous boundary conditions, a geometrically simple design that retains the essential fluid dynamics and thermochemical processes that occur in actual gas turbine combustors, and unrestrictive access for laser and optical diagnostic measurements. After discussing the design detail, a preliminary investigation of the performance and operating envelope of the combustor is presented. With the combustor operating on premixed methane/air, both the equivalence ratio and the inlet velocity were systematically varied and the flame structure was recorded via digital photography. Interesting lean flame blowout and resonance characteristics were observed. In addition, the combustor exhibited a large region of stable, acoustically clean combustion that is suitable for preliminary validation of LES models.     

Large eddy simulation of turbulent premixed combustion flows over backward facing step

Large eddy simulation (LES) of turbulent premixed combustion flows over backward facing step has been performed using a dynamic sub-grid G-equation flamelet model. A flamelet model for the premixed flame is combined with a dynamic sub-grid combustion model for the filtered propagation of flame speed. The objective of this study is to investigate the validity of the dynamic sub-grid G-equation model in a complex turbulent premixed combustion flow. For the purpose of validating the LES combustion model, the LES of isothermal and reacting shear layer formed at a backward facing step is carried out. The calculated results are compared with the experimental results, and a good agreement is obtained.     

Large eddy simulation of turbulent premixed flame in turbulent channel flow

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by usingG-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgridG-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic subgridG-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.     

Large eddy simulation of turbulent premixed combustion flow around bluff body

Large eddy simulation (LES) of turbulent premixed flame stabilized by the bluff body is developed by using sub-grid scale combustion model based on the G-equation describing the flame front propagation. The basic idea of LES modeling is to evaluate the filtered-front speed, which should be enhanced in the grid scale by the scale fluctuations. The dynamic sub-grid scale models newly introduced into the G-equation are validated by the premixed combustion flow behind the triangle flame holder. The objective of this study is to investigate the validity of the dynamic sub-grid G-equation model to a complex turbulent premixed combustion such as bluff body stabilized turbulent premixed flames for realistic engineering application. A new turbulent flame speed model, introduced by the sub-grid turbulent diffusivity and the flame thickness, is also proposed and is compared with the usual model using sub-grid turbulent intensity and with the experimental data. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment data.     

中心给粉旋流燃烧器气固两相流动的数值模拟

电厂采用的煤粉燃烧技术应达到稳燃、低污染、防结渣及防高温腐蚀的要求。中国电厂燃用煤的煤质偏差,煤种多变。在燃用这些煤的时候,锅炉的稳燃能力较低。针对这些问题,提出中心给粉旋流煤粉燃烧技术。由于燃烧器的气固流动特性对燃烧器的性能有很大的影响,利用可实现的k-ε和Lagrangian随机轨道模型对中心给粉旋流燃烧器的气固两相流动进行数值模拟,并将计算结果和三维相位多普勒测速技术(Phase-Doppler anemometry,PDA)试验结果进行详细比较,计算值和试验值速度分布的趋势基本相同。计算和试验结果表明,在轴向方向产生了回流区,切向速度分布出现典型的Rankine涡结构,中心线附近区域的径向速度小。当颗粒的轴向速度衰减为0之后,颗粒的运动方向发生偏转,开始向后上方运动。颗粒迂回型运动轨迹延长了煤粉在回流区中的停留时间。