燃烧加热污染空气对超燃冲压发动机性能影响研究

针对燃烧加热地面试验设备存在的工质污染问题,采用数值模拟方法研究了燃烧加热污染空气对氢燃料超燃冲压发动机性能的影响。以飞行马赫数Ma=6.5,当量油气比ER=0.6为计算基准状态,分别对纯净空气和污染空气来流下氢燃料超燃冲压发动机的整机流场和性能进行了对比计算分析。燃烧化学反应模拟采用了改进的H₂/O₂七组分八方程模型,湍流模型为标准的 k-ε模型,并采用直连式燃烧室试验数据进行了数值方法的验证。研究结果表明:(1)相对于纯净空气来流,污染空气来流下的超燃冲压发动机推力和比冲均有所下降。(2)采用酒精燃烧加热器的前提下,来流参数匹配静温、静压、马赫数时,发动机性能与纯净空气来流下的结果最为接近,而匹配总温、总压、马赫数时相差最大。(3)来流参数匹配总焓、静压、马赫数的前提下,采用氢燃烧加热器时发动机性能与纯净空气来流下的结果最为接近,而采用甲烷燃烧加热器时相差最大。      

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。     

超音速飞机压强场的机器学习预测方法研究

超音速飞行过程中由于近场空气压强过大而产生音爆现象,会对周围环境产生重要影响。准确预测飞机近场和远场的压强值,对超音速飞机设计和评估极其关键。首先通过Fluent计算飞机在不同马赫数下近场的压强,其次通过机器学习线性回归算法拟合远场的压强场,最后通过模拟数据验证模型的准确性。结果显示,模型预测精度相对误差在5%以内,研究结果可以为超音速飞行器音爆测量与预测提供理论基础。     

某重型燃气轮机燃烧室燃烧流动的数值模拟

对某重型燃气轮机燃烧室燃烧天然气进行数值模拟,在模拟过程中采用了雷诺应力模型、EBU-Arrheniue湍流燃烧模型和六通量辐射模型来描述其燃烧流动过程,运用FLUENT软件求解了三维流场和温场分布.计算结果能够很好地反映该重型燃气轮机燃烧室燃烧流动特点,对预测燃烧室内的燃烧流动有一定参考价值.     

H2O/CO2污染对煤油燃料超声速燃烧影响数值研究

在纯净空气与H₂O/ CO₂污染空气来流对比试验结果基础上,采用数值计算方法和化学动力学方法,研究了H₂O和CO₂污染组分对煤油燃料超声速燃烧的影响,获得了试验手段难以得到的燃烧室流场参数和性能数据。完成了相应的煤油燃料超声速燃烧室二维数值计算,其中匹配了进口总温、总压、马赫数、氧气摩尔分数和工作当量油气比。将数值计算结果与相应试验测量值进行了对比分析,并结合燃烧室流场数据、性能参数分析了H₂O和CO₂污染的动力学影响、以及对燃烧室性能的影响。研究表明:(1)数值计算结果与实验测量值总体上吻合,两种手段均体现了纯净空气来流时不同煤油当量油气比的燃烧室性能,并反映了一致的“污染效应”影响趋势;(2) H₂O污染、H₂O+ CO₂污染的存在降低了煤油燃料超声速燃烧室性能,体现在燃烧诱导压升、燃烧效率、流向冲量增量的下降,而且随着污染组分含量的增加,燃烧室性能下降越加显著。      

安全阀稳态泄放过程的瞬态模拟与试验验证

该文采用瞬态模拟方法对开启过程的稳态泄放流动机理进行了研究,采用路径分析法和流线分析法研究了内部和外部泄放流道中流场参数的变化特点,对比了模型的相关参数在典型路径上的变化关系。分析了流动的跨音速发展和演化情况,进而说明了安全阀与传统喷管在超音速机理方面的异同。同时分析发现喉部并未如传统理论预期出现超音速流,而传统认为不会出现超音速流的阀口流场附近区域(密封面)和反冲盘出口却出现了全面超音速流。利用所开发的实验装置对开启过程参数进行了验证测试。模拟结果与测试数据的对比表明,三维瞬态模拟和实验数据非常吻合。     

燃烧室喷嘴的优化设计与仿真模拟

通过建立圆管状燃烧室内煤粉燃烧的数学模型,对燃烧室回流区的温度场进行数值模拟。通过改变燃烧室的喷嘴形状,数值模拟了温度场的分布规律。结果表明,不同的喷嘴对燃烧有着重要影响,钝体喷嘴最适合该燃烧室的要求。实验表明,数值模拟与实验结果能基本吻合。研究结果对燃烧室的设计和燃烧室工况分析具有指导意义,所建立的数学模型为燃烧室几何和结构设计以及燃烧过程操作中进行定量分析提供了有效手段。     

增压器性能试验台燃烧室的流体仿真与性能优化

在对车用涡轮增压器性能试验台架的研究中发现,燃烧室的燃烧情况会对试验检测结果产生影响。现以燃烧室为研究对象,将其内部几何结构做一定简化后,利用CFD软件FLUENT对其内部冷态动力场和燃烧过程进行数值模拟分析,并通过改变燃烧室中喷油油束的角度和方位及喷油点数量,对改变后的各种情形进行燃烧模拟仿真,寻求在喷油束入射这方面的具体优化方案。结果表明,原型燃烧室结构设计合理,内部冷态动力场分布良好,稳态燃烧时除存在空间分布不均匀外整体情况良好;改变喷油束入射形态确实会对燃烧产生影响,其中将喷油束偏向空气进口和两个喷油点以轴向截面为对称面45°角入射比原型流场分布要好。该结论为增压器试验台燃烧室的设计和优化提供流场理论及建议。     

微加热器热传导试验与计算

为了研究微加热膜下方的结构与微加热器性能的关系,利用数值计算与有限元仿真,研究了微加热膜下方空气隙厚度的变化对加热器性能的影响.首先,通过微加热器试验确定了对流换热系数等关键热学计算参数,建立了一维Fourier导热微分方程组,计算了Biot数并以此为依据对模型进行了薄壁简化,使用有限差分法对微分方程进行了数值计算.然...     

新型材料改性方法——常温超音速冷喷涂制备功能涂层

介绍一种新型材料表面改性技术－冷喷涂技术，即气体在常温下或在有限加热温度下，利用超音速气流将涂层粉末喷射到基板形成保护涂层。相对热喷涂技术而言，其不存在高温氧化、气化、晶化等影响涂层性能的效应出现，具有独到之处。结合工程实际简化建模，并完成气、固两相射流的流场计算结果。定量研究了冷喷涂试验中两相射流流对涂层效果的影响程度。还对该试验装置进行了锌粉、陶瓷粉的膜制备试验，取得了预期效果。     

Starting characteristics of the hypersonic wind tunnel with the mach number variation

The scramjet engine test facility (SETF) of the Korea Aerospace Research Institute is a blow-down, high enthalpy wind tunnel with a free-jet test cell. The free-jet test sections can reduce choking and test larger models compared with solid wall test sections, but the facility needs an excessive starting pressure ratio and is highly unpredictable because of the free-jet space. An air ejector system was designed to simulate a Mach 3.5 test condition. Quasi one-dimensional and computational analyses of the ejector were performed. The test results of the ejector well agree with the analysis results. The SETF showed a normal-shock efficiency of 58% at the Mach 3.5 condition. The air ejector system was modified to conduct a scramjet intake test with a Mach 6.7 condition. The normal-shock efficiency of the SETF was 40% with the Mach 6.7 condition. There was almost no change in the starting pressure ratio due to blockage.     

A testing facility for pumps operating in a supersonic flow of a water-steam mixture

A testing facility designed for experimental studies and diagnostic tests of pumps in a supersonic flow of a water-steam mixture, which simulates natural working bodies in the boiling state, is described. The results of studies of pumps on the bench that have shown the possibility of changing to turboless system for supplying fuel into the engines of aircrafts.     

超燃发动机流场组分浓度的在线测量

为了正确评价超燃发动机试验状态,采用自发拉曼散射技术在线测量了超燃发动机流场的主要组分。基于发动机试验条件和发动机与光学诊断技术的接口,建立了用于发动机流场组分测量的自发拉曼散射实验系统;测量了多车次发动机试验过程中流场主要组分的拉曼光谱;最后,通过光谱计算获得了流场主要组分浓度信息并重点分析了来流氧气含量及其变化情况。实验显示:发动机试验中,部分车次试验补氧后的来流中氧气的最大含量达到了30%,最小含量为18%,说明发动机试验过程中,对补氧量的控制精确和稳定性还有待提高。结果表明:采用自发拉曼散射技术可以较好地完成来流主要组分浓度测量工作,测量结果可用于发动机试验数据的分析及来流补氧控制方式和控制精度的改进。     

A facility for permeation measurements under plasma irradiation

An PIM (magnetic plasma source) experimental facility for investigation of permeation of hydrogen isotopes through the structural and plasma-facing materials, which are used in fusion devices, is described. The facility allows investigation of the hydrogen permeation through metal and porous (carbon and carbon composites) membranes in a temperature range of 290–1000 K during interaction of membranes with gaseous hydrogen (the pressure difference between the membrane sides is up to 0.1 atm) and also under irradiation with microwave plasma with a flux density of up to 3 × 10²⁰ atoms/(m² s). The permeability of ChS-68 austenitic steel was investigated. The experimental data confirmed the correctness of the operation of the facility and the reliability of the results.     

Computation and comparison of two electric air heaters for industrial use

The computational results of temperature on the surface of ribbed tubular electric heaters and ribbed pipes of thermosiphons have been presented, the desired airflow rate, and installed electric capacity of fan motors for existing and developed electric air heaters has been determined. The computational results of the temperatures of the ribbed pipes have been compared with the experimental data. The novelty of the development has been confirmed by patents obtained on the invention of the electric air-heater design.     

Imaging of hydrogen-induced Si(111) surface with the scanning tunnelling microscope

We have directly observed the hydrogen-induced changes of the Si(111)7times7 surface using a scanning tunnelling microscope (STM). The 7times7 reconstructed atomic structure was formed on a clean surface of Si(111). But when the clean surface was dosed with typically 1–2 L [1 L (Langmuir) = 1·33 times 10^?4 Pa. sec] hydrogen, the 7 times 7 image was gradually smeared out and then a 1 times 1 unreconstructed pattern appeared. After dosing with 5–10 L hydrogen, the STM image exhibited a new long-periodic structure together with the 1times1 structure underneath. These experimental results may be ascribed to the chemisorption of hydrogen atoms on clean Si surfaces.     

Optimal design of supersonic nozzle contour for altitude test facility

This paper develops a robust and practical design for supersonic nozzles to be used in an altitude engine test facility. Although many studies have been conducted on nozzle design, none of these present a robust yet practical and simple method for designing supersonic nozzles. This research attempts to develop such design for supersonic nozzles by combining method of characteristics (MOC), optimization algorithm, and computational fluid dynamics analysis for design verification. Preliminary design optimal techniques were adopted to reduce nozzle length while keeping the exit area constant in the design. Optimization produced a smooth flow by generating a parallel and uniform flow at the exit. A two-dimensional model was initially used because of the axisymmetrical characteristic of the flow in this study. The optimal nozzle was designed for the operation of a test facility at Mach number 2.3 and altitude of 7 km. The optimal design produced a uniform and parallel flow at the given test condition.     

Design, manufacture, and analysis of metal foam electrical resistance heater

This paper presents a novel concept using the radial heating element made from porous Fe–Cr–Al metal foam in an air heater. Electrical resistance heating has been used extensively to convert the electrical energy into thermal energy. An analytic heat transfer model is first developed to estimate dimensions of the heating element. Four prototype Fe–Cr–Al metal foam electrical heaters with different levels of porosity and density are built. A more detailed computational fluid dynamics modeling of prototype heaters to include the temperature loss to the surroundings is developed. Experiments are conducted to evaluate the effects of airflow rates and electrical current and measure the change of air inlet and outlet temperatures. The experimental temperature measurements show reasonably good agreement with modeling predictions. Finally, improvements to the initial concept are discussed.     

A technique for measuring the propagation of a supersonic radiation front in foam via spatially resolved spectral imaging of a tracer layer

We present a technique for measuring the propagation of a supersonic radiation front in low-density foam, where the lack of motion of the objects in its wake makes it difficult to determine its location. We illuminate a thin tracer foil embedded in the foam with a broadband x-ray source, and measure its changing absorption of these x rays as it ionizes. We record both spatial and spectral information of the heated tracer, and thus obtain its ionization state as a function of distance along the front propagation direction. We extrapolate this information to determine the state of the foam and the location of the radiation front. We present the experimental configuration used to test this technique at the Omega laser facility along with experimental results.     

An experimental study on the effect of square grooves on decay characteristics of a supersonic jet from a circular nozzle

In this experimental work, the effect of square grooves on the structure of a supersonic jet emanating from a circular nozzle has been investigated at three different nozzle inlet total pressures i.e 360 kPa, 550 kPa and 720 kPa. The nominal exit Mach number is 1.8. A new empirical relation for predicting the supersonic core length for grooved nozzle has been suggested. Further, a new parameter “groove effectiveness” has also been suggested to quantify the effect of the groove by using the total pressure data in the supersonic core length. Experimental results suggest that at higher nozzle inlet total pressure, the groove effectiveness plays a minor role. From the jet centreline total pressure data, supersonic core length, the locations at which 50 % and 90 % decay occurs have been obtained. It has been observed that higher groove effectiveness is associated with smaller values of supersonic core length, L_50% and L_90%. Schlieren images of the jet structure shows unsymmetrical shock pattern of jets emanating from a single grooved nozzle.