基于激光布里渊散射的高速气流测试技术

激光布里渊散射是由介质密度涨落引起的一种非弹性散射现象,其散射谱特征参数（频移、线宽）取决于散射角和散射介质压强、温度等参数,通过探测高速气流激光布里渊散射谱,可反演获得高速气流压强、温度等参数。介绍了基于激光布里渊散射原理的高速气流参数测试原理,设计了一种基于法布里 珀罗干涉仪的高速气流参数测试装置,搭建实验平台获取了高速氮气气流的激光布里渊散射谱。实验结果表明,通过激光布里渊散射谱获得的高速气流压强、温度值与理论值相对误差在15%以内。     

Optical measurement of the speed of sound in air over the temperature range 300-650 K

Using laser-induced thermal acoustics (LITA), the speed of sound in room air (1 atm) is measured over the temperature range 300-650 K. Since the LITA apparatus maintains a fixed sound wavelength as temperature is varied, this temperature range simultaneously corresponds to a sound frequency range of 10-15 MHz. The data are compared to a published model and typically agree within 0.1%-0.4% at each of 21 temperatures.     

On the determination of laminar flame speed from low-pressure and super-adiabatic propagating spherical flames

The outwardly propagating spherical flame (OPF) method is popularly used to measure the laminar flame speed (LFS). Recently, great efforts have been devoted to improving the accuracy of the LFS measurement from OPF. In the OPF method, several assumptions are made. For examples, the burned gas is assumed to be static and in chemical equilibrium. However, these assumptions may not be satisfied under certain conditions. Here we consider low-pressure and super-adiabatic propagating spherical flames, for which chemical non-equilibrium exists and the burned gas may not be static. The objective is to assess the chemical non-equilibrium effects on the accuracy of LFS measurement from the OPF method. Numerical simulations considering detailed chemistry and transport are conducted. Stoichiometric methane/air flames at sub-atmospheric pressures and methane/oxygen flames at different equivalence ratios are considered. At low pressures, broad heat release zone is observed and the burned gas cannot quickly reach the adiabatic flame temperature, indicating the existence of chemical non-equilibrium of burned gas. Positive flow in the burned gas is identified and it is shown to become stronger at lower initial pressure. Consequently, the LFS measurement from OPF at low pressures is not accurate if the burned gas is assumed to be static and at chemical equilibrium. For super-adiabatic spherical flames, the burned gas speed is found to be negative due to the local temperature overshoot at the flame front. Such negative speed of burned gas can also reduce the accuracy of LFS measurement. It is recommended that the direct method measuring both flame propagation speed and flow speed of unburned gas should be used to determine the LFS at low pressures or for mixtures with super-adiabatic flame temperature.     

RFQ冷却聚束器的离子引出系统

论述了RFQ冷却聚束器的两种离子引出系统——静电引出和小型RFQ方法的模拟结果，并通过流体力学方法计算了设计中的静电引出系统的氦气流量和系统可能获得的真空度. 研究结果表明：在较低氦气气压时，应该选用小型RFQ引出方法，以获得更好的束流品质，而在较高氦气气压时，只能选用静电引出方法. 另外，由于设计中的RFQ冷却聚束器经常工作于高氦气气压条件下，因此高纯度氦气的回收和再利用是必需的.     

气相井喷的泄漏源模型及其仿真

 钻井过程的井喷是气田开发中最严重的事故之一,研究气相井喷的泄漏和扩散进而为现场应急提供科学依据,必须首先明确钻井过程中井喷的泄漏源模型。采用流体力学特别是气体动力学理论与计算流体力学技术相结合的方法,分析和模拟了气相井喷的泄漏源模型。通过基于理论分析的数值仿真,得到了气相井喷的温度、静压和马赫数分布等气体动力学参数,仿真结果与理论分析以及相关实验的结论具有很好的一致性。研究表明,钻井过程中气相井喷的泄漏源可以用塞流模型表征,气相井喷可视为欠膨胀射流。     

二极管激光吸收光谱法对低气压介质阻挡放电等离子体中氩的亚稳态的诊断

利用可调谐二极管激光吸收光谱技术对低气压氩气介质阻挡放电等离子体进行诊断,重点考察了Ar亚稳态1s₅和1s₃的数密度和气体温度随放电电压,气压,流量,极板间距,以及随N₂配比的变化情况。实验基于朗伯-比尔(Lambert-Beer)定律,通过计算吸收谱线的吸收峰面积求取Ar亚稳态的数密度,同时对谱线进行Voigt拟合得到多普勒展宽,进而求出气体温度。Ar亚稳态主要由电子碰撞产生,但同时电子也会碰撞亚稳态发生猝灭作用,从而使数密度减少;气体温度则与等离子体的实际功率、电子的状态以及粒子之间的碰撞有关。实验结果表明在本实验条件范围内,Ar亚稳态数密度和气体温度随放电电压和流量的增大都先增大,之后逐渐趋于平缓,但两者随流量的变化幅度都较之随放电电压的小,增长较缓慢。随气压的升高,Ar亚稳态数密度和气体温度先增加并达到一个极大值,而之后逐渐降低。实验数据表明,气压对谱线展宽有较明显的影响作用。适当增大极板间距,Ar亚稳态数密度明显降低,但气体温度却有所升高。N₂的加入对亚稳态有很强的猝灭作用,0.5%的N₂就会使数密度下降50%,但随着N₂浓度的进一步增大,其数密度不再明显降低。     

Laser-induced thermal-acoustic velocimetry with heterodyne detection

Laser-induced thermal acoustics (LITA) was used with heterodyne detection to measure simultaneously and in a single laser pulse the sound speed and flow velocity of NO>(2) -seeded air in a low-speed wind tunnel up to Mach number M =0.1 . The uncertainties of the velocity and the sound speed measurements were ~0.2 m/s and 0.5%, respectively. Measurements were obtained through a nonlinear least-squares fit to a general, analytic closed-form solution for heterodyne-detected LITA signals from thermal gratings. Agreement between theory and experiment is exceptionally good.     

大气压氩气介质阻挡放电中的电子激发温度

采用发射光谱强度比法,测量了大气压氩气介质阻挡放电(DBD)中的电子激发温度。实验在690～800 nm的范围内测量了大气压氩气DBD的发射光谱,经分析发现这些谱线全部是氩原子的发射谱线。为了测量电子激发温度,选用相距较近的763.51 nm(2P₆→1S₅),772.42 nm(2P₂→1S₃)的两条光谱线。结果发现电子温度的范围为0.1～0.5 eV,电子激发温度随电压的增加而增加,随流量的增加而减小。实验还发现氩气流动与非流动时电子激发温度有明显的差别。上述结果对介质阻挡放电在工业领域上的应用具有重要意义。     

Measurement of neutral gas temperature in inductively coupled plasmas

Dependence of the neutral gas temperature on the gas pressure and discharge power in an inductively coupled plasma source has been investigated using optical emission spectroscopy. Both nitrogen and argon plasmas have been studied separately. In the case of argon plasma, about 5% nitrogen was added to the total gas flow as an actinometer. The maximum temperature was found to be as high as 1850 K at 1 Torr working pressure and 600 W radiofrequency power. The temperature increases almost linearly with the logarithm of the gas pressure, but changes only slightly with the discharge power in the range of 100–600 W. In a nitrogen plasma, a sudden increase in the neutral gas temperature occurs when the gas pressure is increased at a given discharge power. This suggests a discharge-mode transition from the H-mode (high plasma density) to the E-mode (low plasma density). In the H-mode, the gas temperature is proportional to the logarithm of the gas pressure, as in the argon plasma. However, the gas temperature increases almost linearly with the discharge power, which is in contrast to the case of argon plasma. The electron density in the nitrogen plasma is about 10% of that in the argon plasma. This may explain the observation that the nitrogen neutral temperature is always lower than the argon neutral temperature under the same discharge power and gas pressure.     

精细平衡气体动理学格式

流体系统在重力作用下，流体压力可与重力相平衡，达到静力平衡状态.常规的有限差分和有限体积方法无法在离散尺度上保持这种平衡态，常常产生虚假速度等非物理现象.通过将重力源项的体积分改写为网格界面值的加权平均，实现离散条件下压力与重力的精细平衡，得到一种Navier-Stokes （NS）方程的精细平衡气体动理学格式.该格式可以在机器精度上精确地保持等温条件下的静力平衡态以及捕捉平衡态附近的小扰动传播.同时，该格式还能求解自然界中更常见的非等温平衡态.此类平衡态除了要求静力平衡还要求热流平衡.利用提出的格式求解NS方程，可以得到静止（机器精度下的零速度）的非等温平衡态，并且密度和温度分布都具有二阶精度.通过多个算例验证格式的有效性，表明该格式可更好地模拟重力场下的温度、密度的分层流动.     

超声速气膜冷却时的光学性能优化设计

高速飞行器在大气层中飞行时,其光学头罩承受着严重的气动加热。超声速气膜冷却方法可以有效地隔离外部加热,但是冷却气体和主来流形成的混合层会引起光束退化,影响成像质量。为减少光束退化,优化超声速气膜冷却时的光学性能,基于混合层折射率和压力同时匹配设计思路,提出了两种设计方法,即配置特定温度的冷却气体实现混合层折射率和压力同时匹配设计方法和配置特定组分的冷却气体实现混合层折射率和压力同时匹配设计方法,并对设计方法的可行性和有效性进行了验证。模拟证明,后一种方法在外部流动参数不变的情况下,冷却气体的组分构成仅与其喷流静温有关,为气膜的冷却性能和光学性能同步设计奠定了基础。     

供水温度对CO2空气源热泵系统性能的影响

为探究热泵供水温度对CO2空气源热泵系统性能的影响,保持室外环境温度15.5℃不变,调节热泵供水温度,测试冷却水流量、气冷器出水温度、压缩机排气温度、气冷器CO2进出口温差、压缩机排气压力、压缩机耗功量、系统制热量、气冷器热交换完善度、系统COP的变化情况。结果表明:供水温度由45℃升至85℃,气冷器出水温度、压缩机排气温度、气冷器CO2进出口温差、压缩机排气压力随之增加,冷却水流量随之减小。系统制热量增加了7.3%、气冷器热交换完善度下降了20.0%、系统COP下降了35%、压缩机功耗增加了65.1%。     

大气压氩直流微放电光谱研究

微空心阴极放电或微放电是一种能够实现高气压下放电的有效方法。利用不锈钢空心针作阴极,不锈钢网作阳极,进行了大气压氩直流微放电实验研究。测量了大气压氩微放电光谱,发现氩气的发 射谱线主要集中在690～860 nm范围,且全部为氩原子4p—4s的跃迁。实验研究了不同放电电流、气体压强、气体流量与谱线强度之间的关系,发现谱线强度随放电电流、气体流量增加均增加,而谱线强 度随压强变化呈现不同特征：谱线强度随压强的增加先增加后降低,在13.3 kPa时强度最大。此外,选用跃迁波长为763.51和772.42 nm的两条光谱线,利用发射谱线强度比值法测量了氩气微放电等离子 体的电子激发温度。结果显示,其电子激发温度处于2 000～2 800 K之间,且随放电电流的增加而增加,随气体压强和气体流量的增加而降低。     

高温高压下基于TDLAS的二氧化碳浓度测量方法研究

通过具有高灵敏度、非侵入式等特性的可调谐二极管激光吸收光谱技术对发动机气缸工作过程等高温高压燃烧环境进行实时在线检测,是了解其内部燃烧过程进而研发高效发动机的重要手段之一。作为一种重要的温室气体和化石燃料燃烧的主要产物,二氧化碳对于了解燃烧过程具有重要的意义。为了寻找一种能够对高温高压燃烧过程中的二氧化碳浓度进行快速检测的方法,利用工作在室温条件下的近红外可调谐二极管激光器作为光源,以二氧化碳位于5 006.140 cm-1处的跃迁作为传感谱线,结合固定波长的吸收光谱调制技术,通过该CO₂谱线的一次谐波归一化的二次谐波信号峰值实现对高温高压环境中CO₂浓度测量,建立了一种可用于高温高压环境下的组份浓度的测量方法,通过实验验证得出该方法在5 atm压力、500 K温度下和10 atm压力、1 000 K温度下对于CO₂浓度测量的平均标准偏差为3.99%;另外还对实验中所得CO₂直接吸收及二次谐波信号进行了分析,得到了其吸收光谱在高温高压环境下的特性。     

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采用两相流的流动换热理论,建立二维几何模型,运用FLUENT对稳定入口流速下注入气体的铅铋流动段作了模拟。模拟研究注入气体的体积份额或速度改变对压力和铅铋与注入气体之间换热与影响,得到了不同条件下的温度与压力分布。分析结果发现,体积份额减小,铅铋流体的径向温度分布更加均匀,中心温度更低;随着体积份额的减小,铅铋的总压呈现出一种下降的趋势。注入气体速度不同对铅铋整体的换热影响不大;中心处的动压有较大增加,总压改变甚微。     

高焓膨胀管风洞性能调试试验研究

为评估新建成的高焓膨胀管风洞的设备性能,开展了风洞调试试验.通过测量激波速度、静压及Pitot压力等流场参数,结合考虑高温热化学效应的理论计算方法,对设备在常规氦气驱动模式及自由活塞驱动模式、低焓到高焓的运行状态进行了调试与分析.调试试验表明风洞最高气流速度达到11.5 km/s,最高焓值达到71.7 MJ/kg,高焓...     

原表面回热器换热阻力特性试验研究

本文对研制加工的适用于 100 kW 微型燃气轮机的 CW(Cross Wavy) 原表面回热器进行了试验研究,通过对两侧流体进、出口温度、压力等的测量,重点分析了燃气流量、入口温度及空气进口压力变化对换热阻力的影响,得出了在变工况下回热器的流动与换热性能规律,结果表明:所研制的 CW 原表面回热器空、燃气两侧换热均匀,提高了换热效率,两侧压降都有不同程度降低,并得出了有工程应用价值的 Nu-Re 及 f-RE 准则关系式,可为原表面回热器的设计制造提供参考.     

The Flow Patterns and Wall Stresses in a Louvered‐Wall Moving Granular Filter Bed of Quartz Sand

The flow patterns and wall stresses in a two‐dimensional louvered moving granular filter bed of quartz sand were investigated. The flow pattern histories of granular solids in the filter bed were recorded using a digital camcorder and a pressure gauge for simultaneously measuring the normal stresses as well as shear stresses of the granular solids. The static wall stress distributions produced by the granular solids were measured, and agreed with a theoretical prediction formed using the differential slice and Runge‐Kutta (order four) methods. The variations in the dynamic wall stresses with time in a moving granular filter bed were obtained and the effect of the louver angle upon the flow patterns and wall stresses was also investigated. Employing the results obtained by stress measurements and image processing, the wall pressure pulsation phenomena in a moving granular filter bed may be further understood. The results reported here provide fundamental information for the design of moving granular filter beds to act as high‐temperature flue gas cleanup filters.     

Numerical simulation of plasma and fluid behavior in the ISTEC-2 nonequilibrium disk MHD generator with multiple loads

Plasma and fluid behavior in a nonequilibrium disk magnetohydrodynamics generator with multiple loading has been investigated with a time-dependent three-dimensional numerical simulation. Particular attention is paid to the effects of the downstream load resistance and the influences of the middle electrode on the plasma and fluid flow. The possibility to improve generator performance by multiple-loading operation is also examined. It is shown that increase in the downstream load resistance raises the static pressure and decelerates the working gas in the upstream region. This is because the static pressure increase and the boundary layer development near the middle electrode have the same effects as the change of the outlet boundary conditions for the upstream region. It is found that the ionization degree of seed atoms is kept high on the middle electrode, whereas, the electron temperature is decreased rapidly. This results from the longer relaxation time of ion number density compared to that of the electron temperature. The multiple-loading operation leads to an improvement of the enthalpy extraction ratio. Isentropic efficiency, however, becomes somewhat lower under the multiple-loading condition. This is caused by the high static pressure and the low electrical efficiency under the high enthalpy extraction condition for the multiple loading.     

利用波长调制光谱技术测量高温环境中的气体压强、温度和H_2O组分浓度

利用基于可调谐半导体激光器的扫描波长调制光谱技术,实现了高温燃烧场内气体参数的测量。提出了基于迭代算法实现气体压强、温度和组分浓度同时测量的方法,迭代算法具有收敛速度快以及对初始值不敏感等优点。采用频分复用技术,利用两条H_2O吸收谱线(7 454.45和6 806.03cm-1)的谐波信号,对高温燃烧场进行了实验研究,并将气体压强、温度和H_2O组分浓度测量结果与压力传感器、热电偶和直接吸收光谱法的测量结果进行比较,结果表明,基于波长调制光谱技术测得的气体压强、温度和H_2O浓度与预测值基本符合,最大偏差分别在7.6%,8.1%和7.5%以内。此方法具有多参数同时测量、免标定等显著优势,但由于依赖的参数较多,容易对测量精度造成影响。