CFD Study of NO_x Emissions in a Model Commercial Aircraft Engine Combustor

Air worthiness requirements of the aircraft engine emission bring new challenges to the combustor research and design. With the motivation to design high performance and clean combustor, computational fluid dynamics (CFD) is utilized as the powerful design approach. In this paper, Reynolds averaged Navier-Stokes (RANS) equations of reactive two-phase flow in an experimental low emission combustor is performed. The numerical approach uses an implicit compressible gas solver together with a Lagrangian liquid-phase tracking method and the extended coherent flamelet model for turbulence-combustion interaction. The NOx formation is modeled by the concept of post-processing, which resolves the NOx transport equation with the assumption of frozen temperature distribution. Both turbulence-combustion interaction model and NOx formation model are firstly evaluated by the comparison of experimental data published in open literature of a lean direct injection (LDI) combustor. The test rig studied in this paper is called low emission stirred swirl (LESS) combustor, which is a two-stage model combustor, fueled with liquid kerosene (RP-3) and designed by Beihang University (BUAA). The main stage of LESS combustor employs the principle of lean prevaporized and premixed (LPP) concept to reduce pollutant, and the pilot stage depends on a diffusion flame for flame stabili-zation. Detailed numerical results including species distribution, turbulence performance and burning performance are qualita-tively and quantitatively evaluated. Numerical prediction of NOx emission shows a good agreement with test data at both idle condition and full power condition of LESS combustor. Preliminary results of the flame structure are shown in this paper. The flame stabilization mechanism and NOx reduction effort are also discussed with in-depth analysis.     

Design and Performance of an Improved Trapped Vortex Combustor

 A trapped vortex combustor (TVC) has been a very promising novel concept for it offers improvements in lean blow out, altitude relight, operating range, as well as a potential to decrease NO_x emissions compared to conventional combustors. The present paper discusses the improved designs of the new combustor over the prior ones of our research group, including that: a) the overall dimensions, both axial and radial, are reduced to those of an actual aero-engine combustor; b) the air flow distribution is optimized, and especially 15% of the air is fed into the liner as cooling air; c) a straight-wall diffuser with divergence angle 9癷s added. A series of experiments (cavity-fueled only, under atmospheric pressure) has been conducted to investigate the performance of the improved TVC. Experimental results show that at the inlet temperature of 523 K, the inlet pressure of 0.1 MPa, stable operation of the TVC test rig is observed for the Mach number 0.15-0.34, indicating good flame stability; the combustion efficiency obtained in this paper falls into the range of 60%-96%; as the total excess air ratio increases, the combustion efficiency decreases, while the increase of the inlet temperature is beneficial to high combustion efficiency; besides, the optimal Mach numbers for high combustion efficiency under different inlet conditions are confirmed. The outlet temperature profiles feature a bottom in the mid-height of the exit. This paper demonstrates the feasibility for the TVC to be applied to a realistic aero-engine preliminarily and provides reference for TVC design.     

亚燃冲压模型燃烧室高空负压试验

为了验证亚燃冲压燃烧室在高空负压条件下稳定工作的能力,设计了带蒸发式值班火焰稳定器与直射式喷油装置的亚燃冲压模型燃烧室,对该模型燃烧室进行了冷态流阻试验、贫油熄火边界试验以及不同截面燃烧效率试验研究。研究结果表明,试验件的冷态流阻系数略大于1,冷态总压恢复系数0.98以上;蒸发式火焰稳定器贫油熄火边界较宽;两截面燃烧效率最低相差6%,最高相差19%,在高空负压条件下,增加燃烧段长度能显著提高燃烧效率。     

高性能半导体激光器温度控制单元的设计

研究了半导体激光器温度控制系统的设计,包括高精度温度测量电路和大电流半导体制冷片(TEC)驱动电路以及制冷片保护电路。实验表明系统抗干扰能力强,动态响应速度快,控温效果好,在-40-55℃宽范围内半导体泵浦头温度控制精度可达±0.2℃。     

TC4-DT钛合金高温热变形行为研究

利用Gleeble-3500型热模拟实验机,研究了TC4-DT损伤容限型钛合金在温度850℃～1000℃、应变速率0.01～10s-1、变形程度为40%～70%条件下的热变形行为,分析了该合金的流变应力行为及微观组织演变规律,并建立了本构关系模型。研究结果表明,TC4-DT合金在950℃以下的较低温度变形时应力软化现象非常明显,变形机制和热变形激活能不同于950℃以上的较高温度变形机制;在950℃以上高温度变形时,低应变速率(如ε=0.01s-1)促进了动态再结晶行为的发生,而在较高的应变速率(如ε=10s-1)时,一般只发生动态回复现象,动态再结晶行为受抑制。     

航天用复合材料结构高温极限承载能力试验方法

针对航天飞行器飞行特点,本文给出两种基于破坏时间的承载能力试验方法,可以获得结构在不同飞行温度和时间下的承载能力。能够充分发挥材料在传热过程中的高温承载能力,降低结构防热质量。     

基于ANSYS对遥感器铝合金镜头低温环境试验技术的研究

为了给新型遥感器用铝合金镜头提供良好的模拟试验环境,针对较低的温度以及较高的温度均匀性要求,为提高试验可靠性和工作效率,采用仿真计算与试验相结合的方式。运用ANSYS软件详细分析试验过程中的三维温度场,预测整个过程的降温趋势,以提前发现试验中可能存在的潜在问题并做出有效的改进。同时开展低温条件下的试验验证。结果表明:仿真计算值与试验结果趋势相符。通过仿真分析提前预测潜在的问题并对试验方案做出改进,有助于提高试验的可靠性和效率,也为日后的各类金属镜头的低温试验奠定了基础、积累了经验。     

航空发动机燃烧室声载荷自激励门限自回归仿真模型

采用自激励门限自回归分析方法,利用航空发动机环形燃烧室测试数据,得到燃烧室噪声声压时间信号自激励门限自回归仿真模型SETAR（2;1;15,14）,并与控后非门限的自回归滑动平均模型ARMA（6,5）进行了比较,仿真结果表明,误差方差明显降低。     

脉管制冷机液氦温区高频特性

从主动制冷的角度,探索冷端无运动部件的低温制冷机-脉管制冷机高频下达到液氯温区的条件,在前期理论设计的基础上,研制了一台预冷型的单级高频脉管制冷机,采用低温惯性管和低温气库为调相方式,开展了频率、平均充气压力、预冷温度以及输入功率等对制冷机性能影响的实验研究.实验结果表明:当采用氦-4为工质,预冷温度为4.54 K,工作压力为0.775 MPa,工作频率为40 Hz时,该制冷机最低无负荷制冷温度达4.23 K.     

激光推进辐射击穿温度特性的数值研究

在9种等离子体击穿温度下,数值模拟了二次反射式聚焦系统聚焦情况下激光推力器内流场的演化过程,得到了不同击穿温度对应的能量沉积率、推力峰值、冲量和冲量耦合系数,能量沉积率和推进性能参数在某个等离子体击穿温度值处发生突变。根据空气对激光的逆韧致吸收系数公式,计算了CO2激光辐照下不同等离子体击穿温度对应的空气辐射自由程,发现当等离子体击穿温度为14000K时,辐射自由程为1.4mm,与计算网格的典型尺寸相当,此时入射激光能量在一个网格内以一定效率被吸收,由此确定了基于逆韧致吸收的激光等离子体的击穿温度。