连续波DF/HF化学激光器环形喷管与线形喷管的对比

环形喷管阵列主要用于环柱型化学激光器,它可以分为两种构型:直喉道型和圆喉道型。二者都可以由线性喷管阵列变换得到。在变换前后保持相同的增益区体积的前提下,环形喷管阵列的横向尺寸将减小为线性喷管阵列的1/π倍,这将更有利于激光器的紧凑化设计。由于圆喉道型环形喷管阵列相对直喉道型更具实用价值,通过三维的数值模拟,比较了圆喉道型环形喷管单元和线形喷管单元的流场特性。结果表明:在相同截面尺寸及喉道面积的条件下,环形喷管出口气流马赫数、气流速度分别比线形喷管高4.03%,0.356%,静温、静压分别比线形喷管低6.08%,19.7%。在喷管的收缩段,两种喷管的边界层发展规律及厚度值基本相同,而环形喷管的气流速度要快于线形喷管,因此环形喷管的氟原子复合比例要略低于线形喷管。     

CW—DF／HF化学激光器新型喷管气流掺混的数值模拟

针对HYLTE喷管的三维复杂外形,设计生成高效的计算网格.利用有限体积方法,通过求解带湍流模型的多组分混合气体N-S方程,建立了一套能对HYLTE喷管和光腔流场进行模拟的三维程序和方案.考虑到副喷管粘性边界层对喷管内流场的影响,喷管和光腔采用了一体化模拟,在不考虑化学反应的条件下,初步对HYLTE喷管和光腔"冷流场"进行了模拟.研究了喷管和光腔内的流场结构;氧化剂、燃料和稀释剂的掺混机理;喷管内的回流和气体分离等.所得到的冷流场结果可以作为反应流场模拟的初解,对程序进一步完善和反应动力学参数进行修改,可以模拟各种燃料体系和HF泛频激光的反应流场、小信号增益和FP腔的输出功率以及化学效率.(PC7)     

圆转矩形收敛段型面对喷管流动与红外辐射特性影响

针对圆转矩形收扩喷管的收敛段截面面积沿轴向的变化规律进行了优化设计,得到了4种圆转矩形收敛段模型,与相同的矩形扩张段相匹配,形成4种圆转矩形收扩喷管模型,对其气动、换热与红外辐射特征进行了数值研究。得到如下结论:收敛段截面积沿程变化规律对喷管气动与红外辐射特性影响明显:按照前急后缓规律设计的喷管红外抑制效果较差,按照维托辛斯基公式以及缓急相当规律设计的喷管略有增强,而按照前缓后急规律设计的喷管则最佳。这是因为在模型C中随着收敛段截面积沿程收敛速度较快,壁面压力峰值减小,出口旋流增强,尾喷流掺混增强,尾喷流高温区长度减小,尾喷流和喷管红外辐射强度分别降低19.2%和20.6%。     

DSMC方法在微小喷管流场模拟中的应用

利用DSMC方法对不同扩张比及喉部尺寸的轴对称拉伐尔喷管流动现象进行了模拟分析,模拟中采用与实际分子碰撞过程更为接近的内能松弛模型及CLL物面反射模型。研究结果表明不同的扩张比及喉部尺寸对喷管内的流场分布有较大影响,在同等条件下,喉部尺寸较大的微喷管性能要优于喉部尺寸小的喷管,扩张比为5的微喷管流场马赫数更高而壁面承受压力更低,有更好的性能。     

微喷管内流动和换热的数值模拟与分析

发展了直接模拟MonteCarlo方法的压力边界条件处理方法 ,并使用这种方法对微型拉法尔喷管内的气体流动特性进行了数值模拟与分析。研究了两种构型的拉法尔喷管 ,对比了相同出口压力不同入口压力下的流场特性 ,以及在相同入口压力时真空压力条件和给定低压边界条件对流场的影响     

气动激光器列阵喷管的研究

在过去实际工作的基础上(1971～1976),总结了气动激光器快速膨胀喷管设计时应考虑的一些问题,包括主要参数的选择、喷管理论型壁的计算和边界层修正方法的讨论等.同时,通过大量的计算分析,给出了不同条件下边界层修正的简便方法.在过去实际工作的基础上(1971～1976),总结了气动激光器快速膨胀喷管设计时应考虑的一些问题,包括主要参数的选择、喷管理论型壁的计算和边界层修正方法的讨论等.同时,通过大量的计算分析,给出了不同条件下边界层修正的简便方法.     

微喷管内流动和换热的数值模拟与分析

发展了直接模拟Monte Carlo方法的压力边界条件处理方法,并使用这种方法对微型拉法尔喷管内的气体流动特性进行了数值模拟与分析.研究了两种构型的拉法尔喷管,对比了相同出口压力不同入口压力下的流场特性,以及在相同入口压力时真空压力条件和给定低压边界条件对流场的影响.     

仿生毛发气流传感器在流场中的传感特性研究

模仿昆虫感受器的结构,设计制备了一种仿生毛发气流传感器——表面对称电极含金属芯聚偏氟乙烯(PVDF)纤维（SMPF）传感器。基于流体力学理论和第一类压电方程建立了SMPF的气流传感模型。搭建了实验系统,验证了SMPF对于气流速度的传感能力。实验结果表明,SMPF的输出信号和气流速度的平方成线性关系,验证了理论模型,表明SMPF具有感知气流速度的能力。将纤维呈阵列排布置于风洞流场中,用气流对纤维阵列进行冲击,搭建实验系统,验证了纤维在流场中的传感特性,并进行有限元仿真分析。实验结果表明,在风洞装置中,当有气流流过时,会产生流动边界层,且沿着气流速度方向边界层厚度越来越厚,同一截面上的气流速度差也越来越大。实验结果验证了理论模型,表明SMPF具有感知流场分布的能力。     

基于扫描波长调制光谱的气体质量流量测量方法研究

基于扫描波长调制光谱方法实现了超声速气流的温度、H2O组分浓度、压强、速度以及质量流量的测量。利用两条H2O吸收谱线的谐波信号,研究了均匀流场中超声速气流多参数同时测量的方法。基于波长调制光谱技术的测量结果能准确反映均匀流场中的气体参数,然而实际流场往往具有边界层。针对具有边界层的近似均匀流场,数值仿真研究了谱线选择和边界层厚度对流场中心流测量结果的影响。仿真结果表明,随着边界层厚度不断增大,测量结果误差逐渐增大,选择对边界层温度不灵敏的吸收谱线能够有效降低边界层的影响。对超燃直连台隔离段内的超声速气流进行实验研究,结果表明基于波长调制光谱的测量方法在强噪声和强振动的环境中具有较高的测量精度。温度、H2O组分浓度、压强、速度以及质量流量测量值与预测值的最大相对偏差分别在8.2%、7.2%、2.0%、3.1%和6.4%以内。     

微喷管内流动和换热的数值模拟与分析

发展了直接模拟Monte Carlo方法的压力边界条件处理方法，并使用这种方法对微型拉法尔喷管内的气体流动特性进行了数值模拟与分析。研究了两种构型的拉法尔喷管，对比了相同出口压力不同入口压力下的流场特性，以及在相同入口压力时真空压力条件和给定低压边界条件对流场的影响。     

采用超音速低温喷管的小型连续波DF化学激光器性能分析

针对一台单喉道的小型连续波DF化学激光器设计指标与实验结果的差别 ,利用数值方法对不同条件的喷管光腔冷流场进行模拟和诊断 ,分析了光腔中的F原子质量百分比浓度、静压和静温分布以及反应流场小信号增益系数分布 ,并与实验光斑定性地进行了比较 ,取得与实验观察一致的结果 ,从而为该小型DF激光器的改进措施确定提供了理论依据。     

均匀液滴喷射成球法的射流速度计算

分别通过流体力学计算、数值模拟及实验方法研究在不同压力作用下生产电子封装用锡球时不同喷嘴的射流速度。对比分析表明,理论计算和模拟与实验结果基本相符;理论计算方法较方便、准确计算出射流出口的平均速度,数值模拟方法不但可求得平均速度,而且可得到射流断面的速度分布。保持喷嘴直径不变,射流速度随压力增加而呈抛物线形增加。在相同压力作用下,射流速度随喷嘴直径增加而稍有增加,随过渡段直径增加而减小,并且压力差越大增加值或减小值也越大。     

DF/HF化学激光器喷管设计和数值模拟

简述了喷管作用和单个喷管型面设计中存在的问题 ,根据气动理论提出了一种喷管设计新方法 ;介绍了DF HF激光器喷管流动数值模拟的控制方程、初边值条件和CS方法。     

Hydrodynamic Simulations of Unitraveling-Carrier Photodiodes

We present simulated results of a unitraveling-carrier photodiode (UTC-PD) using the hydrodynamic carrier transportation model. A maximum responsivity of 0.25 A/W and a small-signal 3-dB bandwidth of 52 GHz were obtained for a 220-nm-thick InGaAs absorption layer. The physical properties of the UTC-PD have been investigated at different optical injection levels. Modulation of the energy-band profile due to the space charge effect has been observed at high injection level, and an electron velocity overshoot of 3 x 10⁷ cm/s has been found to effectively delay the onset of space charge effects. Comparisons with reported simulated results using the drift-diffusion model as well as reported experimental results are presented. The results suggest the necessity of using the hydrodynamic transport equations to accurately model the UTC-PD. In addition, it has been corroborated that the photoresponse of the UTC-PD could be improved by incorporating a graded doping profile in the absorption layer.     

Design and analysis of separate-absorption-transport-charge-multiplication traveling-wave avalanche photodetectors

This paper proposes a novel type of avalanche photodiode-the separate-absorption-transport-charge-multiplication (SATCM) avalanche photodiode (APD). The novel design of photoabsorption and multiplication layers of APDs can avoid the photoabsorption layer breakdown and hole-transport problems, exhibit low operation voltage, and achieve ultra-high-gain bandwidth product performances. To achieve low excess noise and ultra-high-speed performance in the fiber communication regime (1.3/spl sim/1.55 /spl mu/m), the simulated APD is Si-based with an SiGe-Si superlattice (SL) as the photoabsorption layer and traveling-wave geometric structures. The frequency response is simulated by means of a photo-distributed current model, which includes all the bandwidth-limiting factors, such as the dispersion of microwave propagation loss, velocity mismatch, boundary reflection, and multiplication/transport of photogenerated carriers. By properly choosing the thicknesses of the transport and multiplication layers, microwave propagation effects in the traveling-wave structure can be minimized without increasing the operation voltage significantly. A near 30-Gb/s electrical bandwidth and 10/spl times/ avalanche gain can be achieved simultaneously, even with a long device absorption length (150 /spl mu/m) and low operation voltage (/spl sim/12 V). In addition, the ultrahigh output saturation power bandwidth product of this simulated TWAPD structure can also be expected due to the large photoabsorption volume and superior microwave-guiding structure.     

基于水导激光平面缩流喷嘴内流场仿真研究

适用于水导激光加工工艺的毛细带锥角喷嘴,其内部流动状态复杂。为了获得喷嘴内部高度稳定水束,采用有限元流体计算软件模拟分析的方法,进行了适用于水导激光工艺的缩流型喷嘴内流场模拟分析和数值验证,取得了生成高速稳定水束的参量数据。结果表明,随着平面喷嘴入口压力逐渐增加,毛细段长径比值减小,流体进入喷嘴内部与毛细段壁面发生完全分离,无明显的空化现象发生,形成稳定光滑的缩流型水束;喷嘴入口压力为50MPa时,毛细管直径分别为0.128mm,0.07mm,0.03mm的喷嘴内部水束再附壁长度可达毛细管长度90%;锥角管为10°时, 经过锥角段的水束会再次附壁。模拟分析所得参量对水导激光缩流型喷嘴选取提供指导。     

液体激光系统流场特性对热畸变的影响

液体介质的循环流动为消除激光系统的热效应提供了有效途径,对改善激光系统的光束质量具有重要意义.根据液体介质的流场特性,结合Fluent6.53软件模拟计算,分析了抽运区介质流速、湍流强度与附面层厚度、温度扰动的关系及时激光热畸变的影响.增大抽运区介质流速能有效减小热畸变和附面层厚度;在给定抽运条件下,采用光阑限孔的方法进一步减小热畸变,流速为20 m/s时的光程差(OPD)最人差值由 10个波长下降到5个波长.     

Numerical analysis of fluid flow of rotating squared crystal in the pulling method and its effect on growth shape

A numerical analysis of the effect of a rotating squared crystal on the environmental solution flow in the pulling method was performed. These calculation results show a drastic change in the velocity boundary layer thickness around the squared edge at a certain condition. This velocity boundary layer thickness has generally a strong relation with a solute boundary layer thickness and that corresponds to the difference of the crystal growth rate. We calculate the crystal surface spiral ledge growth rate assuming typical BCF model and with the different solute boundary layer thickness at different positions. This solute boundary layer thickness difference brought different ledge growth rates. We calculate ledge growth rate in the case of the small solute boundary layer thickness near the spiral center and large thickness far from the spiral center. At the region of the two solute boundary layer thickness exists, the higher growth rate ledge that located near the spiral center about to reach the far located and low growth rate ledge. So as a result, the ledge spacing becomes smaller at the boundary of the two different thickness boundary layers.     

Some numerical solutions of the boundary layer equations for an SF6arc

An approximate integral formulation of the thermal boundary layer equation is derived for a steady arc in a nozzle. This differential equation defines the constriction of the arc radius in terms of a heat transfer parameter γ which represents the ratio of all radial heat losses to axial convection. These radial losses include both optically thin radiation and turbulent heat transfer as estimated from a mixing length model. Numerical solutions of the continuity, energy, and momentum equations have been obtained within an arc radius determined from the above equation. These solutions show the effects of various degree of arc constriction upon the velocity and temperature profiles and the arc time constant. The calculations make use of the thermodynamic, transport, and radiative properties of SF6evaluated for a throat pressure of 10 atm for temperatures up to 100 000°K. Solutions have been obtained for arc currents of 100 and 1000 A. It is found that a 100-A arc will have a time constant of several microseconds if the arc radius is of the order of 0.5 mm. Voltage gradients corresponding to this degree of constriction are approximately 200 V/cm.