低污染燃烧室预混喷嘴结构性能的数值研究

以某燃气轮机SAC(单环腔)燃烧室为原型,设计、研究了一种适用于甲烷燃料的低污染燃烧室,对燃烧室单喷嘴模型进行了数值模拟研究。就燃料喷孔位置、旋流器旋流数、叶片数目对流场和温度场进行了定性的分析。结果表明:(1)设计的喷嘴结构能形成明显的中心回流区和角回流区;(2)在有限预混长度情况下,燃料孔的位置对燃料空气预混效果有较大影响;(3)旋流器旋流数及叶片数目对燃烧室冷态流场有较大影响,且旋流数设计过大会导致回火现象,旋流数过低也会对燃料空气预混的均匀性产生一定影响;(4)结构优化后的喷嘴经计算得到NO_x排放量为7.01×10~(-6)(15%O_2浓度),CO为4.687×10~(-6)(15%O_2浓度),相比传统燃烧室降低了约80%,为形成与环境友好的燃烧室设计技术做了理论探索前期的研究工作。     

燃气轮机燃烧室预混结构性能的数值研究

采用Fluent软件对某旋流预混燃烧室燃料与空气的预混和燃烧进行了数值模拟,分析了轴向叶片式旋流器叶片参数对预混均匀性、回火特性、总压损失和污染物排放的影响,并提出了燃料喷孔结构的改进方案.结果表明:旋流器叶片遮盖度为1.0~1.5,叶片角度为40°~55°,叶片数目为8~12时能够获得较好的燃烧性能;缩小燃料喷孔的孔径,采用旋流器与燃料喷孔合并的结构,合理布置燃料喷孔的位置3种改进方案均能有效改善预混均匀性,降低燃烧的最高温度,3种改进方案依次使NO_x的体积分数比原来降低91%、35%和91%.     

微混喷嘴结构对氢混燃料/空气掺混均匀性的影响分析

采用数值仿真方法开展了燃气轮机燃烧室微混喷嘴中富氢燃料/空气掺混均匀性问题研究。首先分 析了三种不同微混喷嘴结构的燃料浓度分布和掺混均匀性指数变化规律，发现采用燃料轴向进气、空气径向 进气的燃料/空气掺混方式，能够在合理的总压损失范围内，获得更好的掺混均匀性。然后分析了三种喷嘴 的流场特性，不同径向位置处的轴向速度分布表明，燃料和空气的射流速度会对喷嘴内燃料/空气掺混水平 造成影响，燃料径向喷人和从喷嘴中心区域轴向喷人在轴向高速射流作用下被吹向下游，不能均匀的沿径向 扩散并分布到喷嘴流道内部，使燃料/空气掺混均匀性提高受限。最后分析了富氢燃料中氢含量变化对掺混 均匀性的影响，研究结果表明，氢含量变化会带来燃料射流速度的改变，当燃料射流速度超出合理范围后，会 导致掺混均匀性下降。研究结果为微混喷嘴燃料/空气喷注策略设计提供参考。     

燃烧室预混段燃料_空气混合规律的数值研究

燃料与空气的均匀混合是稀态均相预混燃烧技术的关键.采用数值模拟方法:研究了多种工况条件下一个圆柱形射流预混段内燃料与空气的混合过程.结果显示,增加预混段长度,减小燃料喷嘴直径,降低燃气平均速度和提高燃气湍流度,都能提高预混段的混合能力.研究获得了所有主要参数的统一定量关系,可用它通过内插或外推来预测其它条件下燃料和空气的混合情况.研究结果对于认识预混过程的机理和燃烧室的设计有重要的参考价值.     

同轴分级环形燃烧室低工况燃料分配特性

针对天然气燃气轮机在低工况下的燃料分配策略问题,采用数值模拟研究了7种不同燃料分配模式下的同轴分级环形燃烧室燃烧特性,重点分析了燃料分配模式对速度场、燃料空间分布、温度场以及综合性能的影响。研究结果表明:燃料分配模式是影响燃烧室性能的关键因素,适量控制值班级燃料喷射量可以改善燃烧室内的燃料贯穿深度和温度场分布;预混级虽然可以提高燃料分布均匀性和降低污染物排放,但是会引发回火现象;当燃料通过第一、二级预混级喷入燃烧室时,燃烧室的效率较高、压力损失较小、污染物排放较低。     

微型燃气轮机燃烧室预混结构性能研究及改进

针对微型燃气轮机燃烧室的设计,通过归纳工程中常见结构,对大阪大学的实验装置进行数值模拟及结构改进。结果表明结构中的燃料喷射流量与喷孔位置无关,与喷孔面积呈正相关,且喷孔的开孔位置和孔径大小对燃料与空气混合均匀性有显著影响。比较两种改进结构的反应区最高温度和污染物CO排放指标,表明预混非均匀性的降低对燃烧性能的提高和反应区最高温度的降低有显著的作用。通过改进结构,能够强化预混、减小预混非均匀度,降低最高燃烧温度,但CO的排放会上升。     

空气旋流数对甲烷燃烧NOx生成影响数值模拟研究

为研究甲烷-空气非预混燃烧下空气旋流数对流动特性、温度分布及其对污染物NOx生成的影响,利用CFD软件,采用标准的k-ε湍流模型、P-1辐射模型和涡流耗散模型进行数值模拟。结果表明：空气旋流数从0提高到0.8的过程中,形成的中心内回流区会强化燃料和空气混合,中心火焰向燃烧室两侧逐渐扩散,火焰长度变短,且高温区移动到燃烧室的前端,局部高温的产生得到了抑制,燃烧室内的温度场更加均匀,进而导致NOx生成量的下降。同时研究燃烧器几何尺寸对气体停留时间及NOx排放浓度的影响,发现缩小空气入口孔隙半径r和燃空径向隔板间距L会导致气流速度增大,促进反应更快地弥散到整个空间,能够进一步抑制NOx的产生。     

单管微混燃烧器燃料/空气掺混规律研究

为了使应用于燃气轮机的单管微混燃烧器实现清洁燃烧,达到降低污染的效果,采用数值模拟的方法,从影响单管微混燃烧器燃/空掺混均匀性的几何参数入手,分析了几何参数与掺混均匀性的问题,研究了微混燃烧器中非反应流动以及燃/空分配对掺混均匀性的影响,形成了单喷嘴微混设计方案。三维模拟模型基于如下设计参数建立：空气孔径D_a为2～5 m、空气孔间距S为5～11 m、第1排空气孔与燃料主流入口平面距离L₁为3～35 m、流速V为50～70 s。结果表明：混合质量并不直接取决于空气孔直径D_a的大小,而是与燃空射流动量比有关;空气孔间距S对均匀度的影响较小,且与最短预混段长度L呈三次多项式的关系;L₁的长度与预混段长度在给定区间内呈现四次多项式的关系;流速V、空气孔直径D_a、射流深度H三者可呈现出一个函数关系,可由已知量推测未知量的范围。基于上述研究结果,在合适的几何尺寸下,单管微混燃烧器可以得到较高的混合质量,压损较小的情况下,使燃/空掺混均匀性更好。     

生物乙醇喷雾蒸发和预混过程的数值模拟研究

基于生物乙醇燃料的贫燃预混、预蒸发燃烧技术(Lean Premixed Pervaporation,LPP),采用数值模拟方法,研究了预混室内生物乙醇雾化蒸发流场,分析了预热空气温度为500、600和1 000 K以及旋流数为0.47、0.8和1.41时的生物乙醇蒸发和气体混合特性的规律。研究表明:在LPP预混室旋流流场中,中心回流区宽度随预混室距离的增加先增大后减小,并且会受喷雾射流的影响拉伸变长,中心回流区随旋流强度的增大更贴近喷雾出口,角回流区的长度随旋流强度增大而缩短直至消失,旋流强度对液雾整体蒸发速率影响不大,但会影响液雾分布;进气温度增加会增大进气速度,提高液滴蒸发速率,缩短液雾炬长度;液滴蒸发过程存在一定程度上的压力振荡,会对LPP不稳定燃烧过程产生一定影响。     

火焰拉伸对甲烷/空气和丙烷/空气层流燃烧速度的影响

通过拓展层流火焰消耗速度的概念,将其定义与反应进程变量（progress variable）的定义相结合,给出了一个积分层流燃烧速度的广义定义。在准一维稳态系统中,分析了积分层流燃烧速度,以及其与未燃气体的位移速度和已燃气体的位移速度之间的关系。对甲烷-空气和丙烷-空气拉伸层流预混火焰在常温常压下进行了数值计算,研究了在不同当量比下,火焰拉伸对层流燃烧速度的影响,并得出了马克斯坦长度。对基于通过火焰前锋放热率的积分层流燃烧速度和基于燃料消耗率的积分层流燃烧速度进行了比较。结论表明低拉伸火焰的马克斯坦数与渐进分析一致,也与球形火焰获得的实验数据吻合。     

Effect of the Structure Parameters of a Low Swirler on Premixed Characteristics

Combustion with lean premixed and low swirl is an effective way of flame organization.It can improve the flame stability and reduce NOX emission.In this kind of combustion,one of the most important issues is fuel/air premixed characteristics.How the structure parameters influence that issue is figured out through numerical simulation.The structure parameters concerned in the study are as follows.They are shape of blades,number of blades,location and shape of gas jet.The influences of them are analysed with comprehensive consideration of many aspects.With the same light shading rate and stagger angle,the axial swirler with curved blades has worse premixed uniformity and lower pressure loss than the one with straight blades.With the same structure of each blade,the decrease of the quantity of blades does influence the pressure loss,while the quantity of gas jets changes correspondingly.But it has little effect on premixed uniformity in a certain range.However,more blades make contribution to better premixed performance.When the total flow area is the same,the axial and circumferential positions of the fuel jets also greatly influence the premixing process.When the fuel jets are upstream the blades and locate at middle of the vanes,the premixing performance is the best.Meanwhile,the jet direction of the fuel jets is a very important influencing factor of the premixing process.When the fuel jet direction is oblique downward at an angle of 30°to the horizontal,the premixing effect is better than the horizontal outflow,which is better than the oblique upward structure.     

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

This paper investigates one issue related to Large Eddy Simulation (LES) of self-excited combustion instabilities in gas-fueled swirled burners: the effects of incomplete mixing between fuel and air at the combustion chamber inlet. Perfect premixing of the gases entering the combustion chamber is rarely achieved in practical applications and this study investigates its impact by comparing LES assuming perfect premixing and LES where the fuel jets are resolved so that fuel/air mixing is explicitely computed. This work demonstrates that the perfect premixing assumption is reasonable for stable flows but is not acceptable to predict self-excited unstable cases. This is shown by comparing LES and experimental fields in terms of mean and RMS fields of temperature, species, velocities as well as mixture fraction pdfs and unsteady activity for two regimes: a stable one at equivalence ratio 0.83 and an unstable one at 0.7.     

Effect of partial premixing on the sooting structure of methane flames

An experimental investigation of the sooting structure of diluted methane–oxygen counterflow flames is reported for partial premixing in the following two nonpremixed flame configurations:

• Case 1:Nonpremixed flame on the oxidizer side of the stagnation plane,
• Case 2:Nonpremixed flame on the fuel side of the stagnation plane.

Effects of both fuel-side and oxidizer-side partial premixing for Cases 1 and 2 were investigated in a low-strain-rate (∼6–8 s⁻¹) counterflow flame. Computations using OPPDIF code were in excellent agreement with the measured concentrations of major species and [OH]. Distribution of measured soot volume fraction and particle sizes are presented along with measured distributions of C₂ hydrocarbon species. Soot loading can increase or decrease depending on (a) the level of partial premixing, (b) the side of partial premixing (fuel side or oxidizer side), and (c) the nonpremixed flame configuration. Of particular interest is the trend for fuel-side partial premixing of Case 1, where the peak soot loading, the peak soot particle diameter, and the thickness of the soot zone initially decrease and then increase with progressive partial premixing. The trends presented are discussed based on chemical, dilution, and flow-field effects of partial premixing on soot growth in counterflow flames. Unlike previous literature, which focused on soot inception, this work emphasizes the role of partial premixing on soot growth by taking into account the changes in the temperature–time history of soot particulates in addition to the previously reported “chemical” and “dilution” effects.     

旋流冷壁燃烧室燃烧性能的数值分析

为进一步深化对中心空气射流及相关参数影响燃烧室性能变化规律的认识,采用雷诺应力模型(RSM)开展了有无中心空气射流、射流速度与射流孔径对燃烧效果影响的仿真研究。结果表明:增加空气中心射流以及改变相关参数能提高燃烧效率的主要原因在于湍流强度的增强改善了传热性能。壁面附近的协同角是影响旋流冷壁效果的重要因素,协同角越接近90°,越有利于获得较好的冷壁效果。     

Study on nonpremixed methane/air combustion from flame structure and NOX emission aspect for different burner head structures

In the present study, the air turbulator, which is a part of a nonpremixed burner, is investigated numerically in terms of its effects on the diffusion methane flame structure and NO_X emissions. A computational fluid dynamics (CFD) code was used for the numerical analysis. At first, four experiments were conducted using natural gas fuel. In the experimental studies, the excess air ratio was taken constant as 1.2, while the fuel consumption rate was changed between 22 and 51 Nm³/h. After the experimental studies, the CFD studies were carried out. Pure methane was taken as fuel for the simulations. The nonpremixed combustion model with the steady laminar flamelet model (SFM) approach was used in the combustion analyses. Methane‐air extinction mechanism with 17 species and 58 reactions was used for the simulations. The results obtained from the CFD studies were confronted with the measurements of the flue gas emissions in the experimental studies. Then, a modified burner head was analysed numerically for the different air turbulator blade numbers and angles. The CFD results show that increasing the air turbulator blade number and angle causes the thermal NO emissions to be reduced in the flue gas by making the flame in the combustion chamber more uniform than the original case. This new flame structure provides better mixing of the fuel and combustion air. Thus, the diffusion flame structure in the combustion chamber takes the form of the partially premixed flame structure. The maximum reduction in the thermal NO emissions in the flue gas is achieved at 38% according to the original case.     

热风循环工艺参数对茯茶烘房的影响研究

以某企业热风循环茯茶烘房为研究对象,应用数值模拟方法研究送风速度、角度和茶砖间距三种单因素变量对烘房的影响规律,结果表明:适当增加送风速度有利于室内空气流动顺畅,并改善温度场的均匀性;送风角度向下偏转有利于提高流场均匀性;缩短茶砖摆放间距,可减少烘房左侧茯茶温度的不均匀。     

Effect of rotor–tower interaction,tilt angle,and yaw misalignment on the aeroelasticity of a large horizontal axis wind turbine with composite blades

This paper presents a detailed analysis of the rotor–tower interaction and the effects of the rotor's tilt angle and yaw misalignment on a large horizontal axis wind turbine. A high‐fidelity aeroelastic model is employed, coupling computational fluid dynamics (CFD) and structural mechanics (CSM). The wind velocity stratification induced by the atmospheric boundary layer (ABL) is modeled. On the CSM side, the complex composite structure of each blade is accurately modeled using shell elements. The rotor–tower interaction is analyzed by comparing results of a rotor‐only simulation and a full‐machine simulation, observing a sudden drop in loads, deformations, and power production of each blade, when passing in front of the tower. Subsequently, a tilt angle is introduced on the rotor, and its effect on blade displacements, loads, and performance is studied, representing a novelty with respect to the available literature. The tilt angle leads to a different contribution of gravity to the blade deformations, sensibly affecting the stresses in the composite material. Lastly, a yaw misalignment is introduced with respect to the incoming wind, and the resulting changes in the blade solicitations are analyzed. In particular, a reduction of the blade axial displacement amplitude during each revolution is observed.     

Knowledge Mining of Low Specific Speed Centrifugal Pump Impeller Based on Proper Orthogonal Decomposition Method

To clarify the complex relation between the pump blade shape and its corresponding hydraulic performance, the knowledge mining method of centrifugal pump impeller based on proper orthogonal decomposition(POD) was proposed. The pump blade shape was parameterized by cubic Bezier curve. The Latin hypercube design method was employed to supply the necessary samples for producing the perturbations of blade wrap angle, and blade angle at inlet and outlet. The hydraulic efficiency and head were optimized by NSGA-II and RBF hybrid algorithm. The Pareto-optimal solutions were obtained. In order to further illustrate the relationship between the centrifugal pump blade shape and its hydraulic performance, the POD method was used to discover the effects of optimized blade shape to the flow solutions. For the optimization of centrifugal pump MH48-12.5, blade shape and relative velocity field in impeller from Pareto-optimal solutions were analyzed. The results demonstrate that larger blade angle and smaller wrap angle increase the average kinetic energy in impeller, resulting in higher pump head design. Smaller blade angle and larger wrap angle decrease the velocity gradient from the pressure side to suction side, resulting in smaller hydraulic loss and higher efficiency design.     

The effect of premixed stratification on the wave dynamics of a rotating detonation combustor

Typical injection schemes of rotating detonation combustors inject fuel locally into the combustion channel, creating stratified fuel-rich and fuel-lean mixing regions. In this study, premixed hydrogen and air rotating detonations are explored in a rotating detonation combustor through premixing part of the fuel into the oxidizer flow. The objective is to investigate the effect of premixing on the operation of the combustor. Three premixing schemes are examined where the detonation wave speeds are analyzed. The results show that in premixing, the fuel-lean regions became more favorable for continuous detonation propagation when premixed with the bypass fuel, resulting in higher detonation wave speeds. This phenomenon is shown to be independent of the global fuel-air equivalence ratio and the amount of fuel premixed into the oxidizer. As such, combustor performance and the operational regime could be improved with lean hydrogen premixing amounts in the main flow oxidizer.     

2种结构喷油嘴的流体动力学(CFD)计算及试验研究

为了满足越来越严格的排放法规和经济性要求,改善柴油机混合气均匀性是有效的措施之一.特别是对于每缸2气门喷油器偏置结构的发动机,燃烧系统开发的一项重要内容是提高喷油嘴各孔流量的均匀性.应用FIRE软件,对无压力室及小压力室2种不同结构的6孔喷油器进行了三维流体动力学（CFD）计算,小压力室结构在流量系数和各喷孔流量的均匀性方面都明显优于无压力室结构.对2种结构的喷油嘴进行了试验对比,小压力室喷油器由于提高了混合气的质量,经济性优于无压力室喷油器.在HC排放量上,无压力室喷油器有很明显的优势。