载气密闭循环氧碘化学激光技术模拟实验研究

载气密闭循环氧碘化学激光器技术是一种有望大幅减小氧碘化学激光器体积和降低运行成本的技术,然而至今鲜见相关实验报道。采用超音速喷管加双螺杆真空泵建成了模拟实验装置,并通过测量超音速喷管前后和双螺杆真空泵出入口处的气动参数的方法开展了载气密闭循环氧碘化学激光器的可行性研究和工作稳定性模拟实验研究。模拟实验研究结果证明了该技术的可行性,发现并分析了其光腔压力随双螺杆真空泵转速提高而出现压力拐点的现象,确定了其稳定运行工作条件,为实现载气密闭循环氧碘化学激光器的真正运行和小型化奠定了良好的基础。     

超音速化学氧碘激光器光腔扩张角

 在超音速化学氧碘激光器的设计中,为了削弱光腔部分的化学反应放热对激光器出光的负面效应,在光腔部分通常加入一扩张角。为了研究这一扩张角对激光器内流场的作用,根据kW级超音速化学氧碘激光器的实验平台,数值模拟了激光器内超音速混合喷管至光腔部分的流动过程,解析了光腔扩张角对内流场的流动参量和化学增益的影响,从维持压强和温度稳定性方面比对分析了不同扩张角度的性能,并探索了喷管高度和扩张角之间的规律。结果表明：此kW级超音速化学氧碘激光器的合理光扩张角度为4.5°。     

高马赫数高压力的氧碘化学激光器阵列喷管的数值模拟

 采用计算流体力学方法,研究了以氮气为载气的新型高总压氧碘化学激光器(COIL)阵列喷管。模拟结果表明:采用高马赫数的氮气流引射低马赫数的氧气流,可以提高光腔出口的驻点压力;高超声速的氮气与声速的氧气混合较慢,在喷管出口安装翼片有利于增强气流混合;喷管出口安装大翼片,翼片诱导的横向涡可以到达氮喷管的中心,光腔内混合比较充分。通过采用10组分21反应的化学反应模型,模拟了阵列喷管内多组分气体的混合和化学反应过程。模拟结果表明：光腔内生成了激发态碘原子和基态碘原子,光腔中获得了正增益,而且光腔出口的总压也由2.6 kPa提升至28.9 kPa。     

新兴的高能激光器——氧碘化学激光器

氧碘化学激光器是近年来国际上竞相研究的一种高能激光器．概述了氧碘化学激光器的基本原理、阐明了提高Ｏ_２（～１△）化学发生器的效率是提高氧碘化学激光器性能的关键；展望了氧碘化学激光器可能的应用前景，指出工业应用或许是氧碘化学激光器近、中期应用的重要方面；简单介绍了中国科学院大连化学物理研究所有关氧碘化学激光方面的研究工作．     

基于故障树的氧碘化学激光器故障分析

为方便快捷地查找出氧碘化学激光器故障发生的原因,以氧碘化学激光器常见故障为例,建立了其功率失常的故障树模型,用最小割集理论按下行法对模型进行了定性分析和定量分析。分析表明:氧碘化学激光器7个子系统中,碘供给子系统的可靠性最低,氯气供给子系统次之,这与实际情况相符。计算出的氧碘化学激光器出光不正常发生概率为3.99%,其可靠度为96.01%。     

kW级立式氧碘化学激光器的初步实验研究

 实验考察了立式氧碘化学激光器的工作性能。在氯气流量为82 mmol/s,无主稀释气的条件下,输出功率约1.3 kW，化学效率达到16.9％。分别与以氦气和氮气为稀释气的氧碘化学激光器进行了主要参数的比较（He-COIL在氯气流量110 mmol/s时，输出功率为2.4 kW；N_{2-COIL在氯气流量115 mmol/s时，输出功率为2.6 kW；立式氧碘化学激光器在氯气流量115 mmol/s时，输出功率为1.32 kW），结果表明该COIL装置初步实验结果与传统的He-COIL和N2-COIL相比还存在很大差距。但通过对实验结果的深入分析得知，若进一步降低单重态氧发生器的pτres值，缩短超音速喷管中亚音速段的氧碘混合长度或采用超音速段氧碘混合方式，使该立式氧碘化学激光器在无主稀释气的条件下运行且达到与He-COIL和N2-COIL相当的功率水平是可以实现的。}     

化学氧碘激光器高压操作的可行性以及最佳增益区的确定

利用一简单的模型,从理论上证明了在化学氧碘激光器小信号增益存在依赖于系统总氧压力的最佳值,同时讨论了高压下工作的化学氧碘激光器的可行性,最后给出了确定化学氧碘激光器的最佳增益区的方法。     

化学氧碘激光器光腔中碘分子浓度的测量

依据Ｂｅｅｒ定律，采用双光路法，利用Ａｒ￣＋激光器的４８８ｎｍ线作为探测激光，对化学氧碘激光器光腔中的碘分子浓度进行了瞬时测量，详细地研究了化学氧碘激光器重要部件之一，激活介质的给体－腆池的工作性能对其他工作参数的依赖关系，并估计了ｋｗ级化学氧碘激光器的最佳氧碘配比约为９０：１．     

氧碘化学激光器故障诊断技术

为了解决氧碘化学激光器通过常规诊断故障定位困难的问题,采用建立的氧碘化学激光器功率失常故障树模型,结合氧碘化学激光器常用的8个监测参数:碘腔压力、碘文氏管压力、p-t曲线、主氦压力、氯气压力、氧发生器压力、上游压力和光腔压力,提出采用故障树和在线监测参数相结合的办法,基于3σ法则的判断标准对氧碘化学激光器进行故障诊断,故障诊断正确率达到94.5%,并对出现的故障提出了改进措施。     

碘喷孔位置的变化对激光性能的影响

 在主、副气流流量不变的情况下,仅改变氧碘化学激光器中碘喷孔的位置,数值模拟了其混合气体流场特性和小信号增益分布等的变化。计算结果表明,碘喷孔在喷管叶片上的位置沿气流方向往下游移动,混合状况变差,光腔中小信号增益降低,输出功率减小,饱和光强沿气流方向的衰减变得平缓。     

气动激光器喷管非平衡流2维数值仿真

将Anderson的两振型三温度弛豫模型和严海星整理的弛豫数据相结合,采用2维守恒型方程组对按照最小长度喷管型面设计方法设计的、面积比分别为50和20的气动激光器喷管非平衡流场进行了数值仿真。小信号增益计算结果在每个计算点都和J.S.Vamos等人针对这两种喷管的小信号增益测量试验结果符合很好.解决了传统的准1维非平衡流分析方法不能很好地和试验结果相符的问题.对气动激光器喷管性能设计提供了更精确的评估方法。     

矩形喷口欠膨胀超声速射流对撞的实验研究

在不同喷口间距和射流压力下开展了矩形喷口欠膨胀超声速射流对撞实验并与自由射流进行了对比. 实验表明:超声速射流对撞的辐射噪声中存在四种不同的啸音模式, 且随喷口距离和射流压力的变化在不同模式间切换. 在射流压力大于0.5 MPa且喷口间距小于50 mm时, 射流对撞面在两个喷口外形成两道正激波之间, 啸音基频维持在3 kHz左右. 随喷口间距的增大或射流压力的降低, 射流对撞面在一侧喷口外的弓形激波与另一侧喷口外的正激波之间. 对撞面也有可能出现在两个弓形激波之间, 对应的啸音基频约为9 kHz, 但容易受扰动而回到喷口一侧或是在喷口之间大幅度振荡. 当射流压力小于0.36 MPa且喷口间距大于70 mm后, 对撞面在两个喷口之间大幅度振荡, 产生基频在1 kHz左右并随射流压力的降低和喷口间距的增大而降低的啸音. 关键词： 超声速射流 啸音 射流对撞 激波     

超音速喷嘴叶栅造型设计及数值分析

分析了超音速喷嘴内部的流动机理并研究了超音速喷嘴的设计方法,对某液体火箭发动机用氢涡轮超音速喷嘴叶栅进行了改型设计。设计采用尖边喉部和光滑过渡喉部两种方法,其中光滑过渡喉部喷嘴型线设计采用具有局部修改能力的三次非均匀B样条曲线。对超音速喷嘴叶栅复杂内流的全三维数值模拟结果表明:改型叶栅流动性能明显改善,效率提高,光滑过渡喉部喷嘴性能优于尖边喉部喷嘴。     

Effects of processing parameters on laser cutting of aluminium-copper alloys using off-axial supersonic nozzles

Conventional laser cutting involves the utilization of converging coaxial nozzles to inject the assist gas used to remove the molten material. This processing system prevents the utilization of this technique to cut aluminium alloys for aerospace applications. The inefficient removal of molten material by the assist gas produces cuts with poor quality; very rough cuts, with a large amount of dross, and a large heat affected zone (HAZ) are obtained. An alternative to increase the assist gas performance is the utilization of off-axial supersonic nozzles. Removal of molten material is substantially increased and cuts with high quality are obtained. On the other hand, pulsed laser cutting offers superior results during the processing of high reflectivity materials as aluminium alloys. However, there are no experimental studies which explore the pulsed laser cutting of aluminium alloys by means of a cutting head assisted by an off-axis supersonic nozzle.The present work constitutes a quantitative experimental study to determine the influence of processing parameters on the cutting speed and quality criteria during processing by means of off-axial supersonic nozzles. Cutting experiments were performed in pulsed mode and the results explained under the basis of the molten material removal mechanisms. Performed experiments indicate a reduction in cutting speed as compared to continuous wave (CW) mode processing and the existence of two processing regimes as a function of the pulse frequency. Best results are obtained under the high pulse frequency one (f > 100 Hz) because the superior capabilities of molten material removal of the supersonic jets are completely exploited in this processing regime.     

Acoustic disturbance from gas non-uniformities convected through a nozzle

The non-steady flow generated by convection of gas containing non-uniform temperature regions or “entropy spots” through a nozzle is examined analytically as a source of acoustic disturbance. The first portion of the investigation treats the “compact nozzle”, the case where all wave lengths are much longer than the nozzle. Strengths of transmitted and reflected one-dimensional waves are given for supersonic and subsonic nozzles and for one configuration of supersonic nozzle with normal shock at the outlet. In addition to a wave reflected from the nozzle inlet, the supersonic nozzle discharges two waves, one facing upstream and the other facing downstream. For reasonable values of the nozzle inlet Mach number, the pressure amplitude of each wave increases directly as the discharge Mach number.The acoustic perturbations from a supercritical nozzle of finite length, in which the undisturbed gas velocity increases linearly through the nozzle, are analyzed for several inlet and discharge Mach number values and over a wide frequency range. The results which agree with the compact analysis for low frequency, deviate considerably as the frequency rises, achieving pressure fluctuation levels of several times the compact values. It is shown that this result originates in a phase shift between the two waves emitted downstream and that the pressure fluctuations for moderate frequencies may be approximated from the compact analysis with an appropriate phase shift.In all cases, the pressure fluctuations caused by a 2% fluctuation in absolute inlet temperature are large enough to require consideration in acoustic analysis of nozzles or turbine blade channels.     

激光推力器喷管热防护实验研究

 基于激光推力器喷管热烧蚀因素分析，初步提出了反射式和吸收式两种喷管热防护方法，并相应设计了两种喷管。以10 kW级脉冲式CO₂激光器为光源，三次反射激光推力器为对象，进行了两种方式下两种喷管的热防护初步实验研究。结果表明：两种喷管均发生不同程度烧蚀，与相对聚焦位置和激光作用时间有关；反射式热防护通过喷管光学表面对透射激光能量进行二次聚焦，以及良好的循环冷却，可能成为将来激光推力器喷管热防护的备选方案之一。     

Control of spray spot shape in cold spray technology. Part 2. Spraying process

The present paper studies high-velocity heterogeneous flows produced with nozzle designs unconventional for cold spray; the process of coating deposition was studied under these conditions. The possibility of using unconventional gas dynamic tools (swirling of main flow, nozzles with permeable profiles and with slots in the supersonic part of nozzle) for control of particle distribution in the supersonic jet is investigated: this might be useful for obtaining a proper shape of the spray spot. These experiments offered a method of gas-dynamic design for the spray spot shape, which extends the possibilities of cold spray technique.     

Control of spray spot in cold spray technology. Part 1. Gas dynamic aspects

This paper presents a study of supersonic jets formed by approaches that are new for cold spray technique: the main flow is swirled, the nozzles with permeable profiles and with exit slots on the supersonic section are engineered. The flow swirling achieved in the nozzle prechamber retains downstream to substrate surface. The system of vortices created within the permeable nozzles changes the shock wave features of the overexpanded jet and the geometry of the bow shock wave ahead of the substrate surface. These new features of flow may affect particle motion and particlesubstrate interaction under the conditions of cold spray process; this offers tools for obtaining the necessary shape of a spray spot.     

Uniform Supersonic Expansion for FTIR Absorption Spectroscopy: The nu(5) Band of (NO)(2) at 26 K

A high-resolution Fourier transform interferometer (Bruker IFS 120 HR) was combined with a uniform supersonic expansion produced by means of axisymmetric Laval nozzles. The geometry profile of the nozzle enabled us to work under precise thermodynamic and kinetic conditions. The effect of the cooling rate of different nozzles on cluster nucleation is illustrated. The experimental sensitivity was tested by recording the nu(5) band of (NO)(2) at 26 K. Copyright 2000 Academic Press.     

任意长度喷管型面设计方法在气动激光器喷管设计中的应用

 将一种新的任意长度喷管型面设计（ALN）方法应用于气动激光器喷管型面设计,在相同的喷管出口设计马赫数、喷管喉部高度及喷管扩张段长度条件下,设计了4条ALN方法喷管型面,并和一条最短长度（MLN）喷管型面作对比,采用2维气动激光器增益场仿真方法对5个喷管的小信号增益场进行仿真。计算结果表明:ALN方法可以有效地实现增益场分布的控制,选择合理的设计参数得到的喷管长度比MLN喷管更短,小信号增益更大。