基于单片机的轴快流CO2激光器控制系统设计【说明书论文开题报告外文翻译】
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毕 业 设 计（论 文）任 务 书1本毕业设计（论文）课题应达到的目的：通过毕业设计，使学生受到电气工程师所必备的综合训练，在不同程度上提高各种设计及应用能力，具体包括以下几方面： 1. 调查研究、中外文献检索与阅读的能力。 2. 综合运用专业理论、知识分析解决实际问题的能力。 3. 定性与定量相结合的独立研究与论证的能力。 4. 实验方案的制定、仪器设备的选用、调试及实验数据的测试、采集与分析处理的能力。 5. 设计、计算与绘图的能力，包括使用计算机的能力。 6. 逻辑思维与形象思维相结合的文字及口头表达的能力。 2本毕业设计（论文）课题任务的内容和要求（包括原始数据、技术要求、工作要求等）：1.本课题要求使用单片机控制轴快流 CO2 激光器。 2.设计系统的硬件电路和软件程序，包括详细的硬件设备配置，系统连接，程序调试等详细步骤； 3.最终完成一篇符合金陵科技学院毕业论文规范的系统技术文档，包括各类技术资料，电路图纸，程序等； 4.系统要有实际的硬件展示，并能够通电运行； 5.本子系统要与整个系统能够配合运行； 6.能够完成各项任务，参加最后的毕业设计答辩。 毕 业 设 计（论 文）任 务 书3对本毕业设计（论文）课题成果的要求包括图表、实物等硬件要求： 1.按期完成一篇符合金陵科技学院论文规范的毕业设计说明书（毕业论文） ，能详细说明设计步骤和思路； 2.能有结构完整，合理可靠的技术方案； 3.能有相应的电气部分硬件电路设计说明； 4.有相应的图纸和技术参数说明。 5.要求控制系统能在实验室现有的设备基础上调试成功，并在答辩时完成实际系统展示。 4主要参考文献： 1 林卫星，激光电源的单片机控制软、硬件设计J，工业控制计算机，2001，14(8)：56-57. 2 李适民，激光器件原理与设计M，华中理工大学出版社，1994. 3 司立众，分立供气轴快流 CO2 激光器占空比配气技术J，制造技术与机床，2012（11）：88-90. 4 江海河，激光加工技术应用的发展及展望J，光电子技术与信息，2001，14(4)：1-12. 5 张育川，我国激光产业十年J，激光与红外，2000，30(3)：136-140. 6 丘军林，我国高功率 CO2 激光器的发展回顾与展望J，应用激光，2002，22(2)：254-254. 7 周稳观等，“现代高功率激光器及其应用”国际研讨会J，激光与光电子学进展，2001，(1)：11-11. 8 潘新民，王燕芳，单片微型计算机实用系统设计M，人民邮电出版社，2000. 9 司立众，一种大功率 CO2 激光切割国产化关键技术研究D，南京理工大学，2009 10 尚建新，单片机原理及其在工业控制中的应用J，太原科技，2003(5)：63-63. 11 C51 Complier Users Guidez. Keil Elektronik Gmb H. and Keil Software, Inc.2000. 12 世界仪器仪表的发展趋势J，仪器仪表与传感器，2003（1）：70-73. 13 孟臣，李敏，串行接口键盘控制器 SK5278 及其在单片机系统中的应用J，国外电子元器件，2003(9)：29-31. 15 陈光东，赵性初，单片微型机算机原理与接口技术M，华中科技大学出版社，2001. 16 司立众，刘旭明，鞠全勇等，一种带工作气体回收再利用装置的轴快流 CO2 激光器P，中国：CN201510291261.8 ，2015-8-5 17 司立众，直流激励轴快流 CO2 非正常放电研究J, 激光与光电子学进展，2012（2）：18 吴秀丽，激光加工的现状及发展趋势J，光机电信息，2000，17(10)：23-23. 19 安承武，李适民等，轴快流 CO2 激光器的气动系统最佳化J，激光杂志，1989，10(2)：53-56. 毕 业 设 计（论 文）任 务 书5本毕业设计（论文）课题工作进度计划：2015.11.04-2015.11.28：在毕业设计管理系统里选题 2015.11.29-2015.12.16：与指导教师共同确定毕业设计课题 2015.12.17-2016.01.10：查阅指导教师下发的任务书，准备开题报告 2016.02.25-2016.03.09：提交开题报告、外文参考资料及译文、论文大纲 2016.03.09-2016.04.28：进行毕业设计（论文） ，填写中期检查表，提交论文草稿等 2016.04.29-2016.05.09：按照要求完成论文或设计说明书等材料,提交论文定稿 2016.05.09-2016.05.13：教师评阅学生毕业设计；学生准备毕业设计答辩 2016.05.14-2016.05.21：参加毕业设计答辩，整理各项毕业设计材料并归档 所在专业审查意见：通过 负责人： 2016 年 1 月 12 日 毕 业 设 计（论文） 开 题 报 告 1结合毕业设计（论文）课题情况，根据所查阅的文献资料，每人撰写不少于1000 字左右的文献综述： 一、选题目的意义高功率轴快流 CO2 激光器的控制系统涉及到的领域较多，对于温度、气压、功率以及各种状态信号等都需要实时监测，各部分的动作要做到安全和互锁，以保证整套激光器安全稳定的运行以及操作人员的绝对安全。PLC 控制技术的引入使轴快流 CO2 激光器的控制系统发生了巨大的变化，极大地增加了激光器控制系统的灵活性，提高了控制系统的效率，丰富了控制系统的资源，扩大了激光器的应用范围。本课题研究的中心主要是围绕单片机控制展开，主要负责控制激光器的外围参数设置各状态监测以及激光器的运行与停止等。随着微型机控制技术的发展，单片机以其独特的性能及优越的性能/价格比独占鳌头，愈来愈受到人们的重视；特别是在家用电器，工业过程控制及智能化仪器中的应用，大有取代微型计算机之势作为上位机的控制面板与下位机 PLC 相配合，很好地完成了对激光器各方面的操作控制， 较好地降低了系统成本，提高了系统的工作效率。 本课题主要是用 C51 系列单片机来完成整个激光器前端控制面板的控制系统，系统的设计可划分为两大部分的内容：一是与单片机直接接口的数字电路范围的电路芯片的设计，如 A/D 芯片的接口。另一部分是与模拟电路相关的电路设计，包括、信号变换、隔离。二、国内外研究综述国外的激光产业已经十分发达。CO2 激光器在工业中的应用一直保持强劲的增长势头，特别是在切割和焊接领域；而在涂覆和打标加工领域，CO2 激光器也同样占有优势。轴快流 CO2 激光器光束质量好，除能连续波工作外，还可门脉冲及超脉冲工作性能稳定，操作简单，维护方便。迄今国际上从 0.5kW 到 3kW 的 CO2 激光切割系统几乎全部选用轴快流 CO2 激光器 。另外国外著名的激光公司也颇具规模，以 RofinSinar 激光公司为例，该公司建于 1975 年。迄今已在世界范围内安装了工业 CO2 激光器 3500 台，占世界中 CO2 激光器市场 28%。近年年销售各种 CO2 激光器约 500 台。1995 年销售额达 1.35 亿马克。我国的激光产业还十分弱小，从严格的意义上来讲还很难算得上一门独立的产业，但是它的发展是迅速的。在引进、消化吸收国外先进技术的同时，我们也开发了自己的产品，20 世纪 60 年代末我国已开始了 CO2 激光器的发展及其应用的研究，经过 30 多年全国科技工作者的努力，现在已形成了 500W10kW 系列产品的生产能力，大约有 10 家公司和单位能够生产 500W 以上的 CO2激光器，其中包括封离型、横流、轴快流等形式。年生产能力已超过 100 台。1991-1998 年销售以年均 40%的速度递增，但从总体上看由于产品质量目前还不如国外产品，因此每年仍有一定数量的产品进口。目前我国激光加工设备产业逐渐走向成熟。大功率激光切割/焊接设备在汽车业将会成倍增长，激光熔覆将会在汽车、船舶、轧钢等行业有一定的应用。专业从事激光切割加工站将会增加。90 年代是我国高功率 CO2 激光器发展比较迅速的时期，由于激光材料加工的迅速推广，特别是激光热处理的普及和 200 多个激光加工站的建立，大大推动了 CO2 激光器的发展。据不完全统计，近十年来，我国激光公司生产的CO2 激光器累计销售已超过 500 台，而从国外公司进口的 CO2 激光器，仅上海团结百超每年就进口上百台。激光加工技术的应用领域主要决定于国家的工业发展状况。我国在 2001年应其中激光打标占了 45.3%居高不下，而全球市场激光切割占整体销售额的37%是激光应用中最大的份额，我国激光切割占 21.7%这其中蕴含着巨大的市场。同时也说明了我国激光产业中的结构不甚合理。其它方面，激光热处理占11.7%焊接占 11.4%打孔占 0.6%其它占 9.3% 。当前，国内、国外市场上销售的美国、日本、德国等的 CO2 激光加工设备大部分 CO2 激光器已采用 PLC 进行控制，其中德国的 Rofin-Sinar 早在几年前就已研制出与 PLC 相配合使用的控制面板，能对激光器进行全面的控制，功能强大，完善，受到市场的欢迎。并且国外公司注重高功率 CO2 激光器的小型化、智能化、可靠性的提高以及完善与数控机床的紧密配合。国内的激光产业这几年发展也很快，但与国外相比还有一定的差距。国内高功率 CO2 激光器就其测控系统而言，仍存在不少问题，其主要问题表现在 ：1、性能较差，功能不多，千瓦以上的 CO2 激光器缺少先进的监测和编程系统； 2 、稳定性还不够高，无故障运行周期短 ；3 一般都脱离不了计算机的外围控制，战线拉得太长。为此，我们研制出以 C51 系列单片机构成的控制系统，该控制系统不仅很好的解决了上述问题，而且使得操作既方便又简捷，更加适合现代激光加工的要求 。三、主要参考文献1 林卫星，激光电源的单片机控制软、硬件设计J，工业控制计算机，2001，14(8)：56-57. 2 李适民，激光器件原理与设计M，华中理工大学出版社，1994.3 吴秀丽，激光加工的现状及发展趋势J，光机电信息，2000，17(10)：23-23. 4 江海河，激光加工技术应用的发展及展望J，光电子技术与信息，2001，14(4)：1-12. 5 司立众，一种大功率 CO2 激光切割国产化关键技术研究D，南京理工大学，2009.6.16 丘军林，我国高功率 CO2 激光器的发展回顾与展望J，应用激光，2002，22(2)：254-254. 7 周稳观等， “现代高功率激光器及其应用”国际研讨会J，激光与光电子学进展，2001，(1)：11-11. 8 潘新民，王燕芳，单片微型计算机实用系统设计，人民邮电出版社，2000.9 安承武，李适民等，轴快流 CO2 激光器的气动系统最佳化J，激光杂志，1989，10(2)：53-56. 10 尚建新，单片机原理及其在工业控制中的应用J，太原科技，2003，(5)：63-63. 11 C51 Complier Users Guide. Keil Elektronik Gmb H. and Keil Software, Inc.2000. 12 世界仪器仪表的发展趋势J，仪器仪表与传感器，2003， （1）：70-73. 13 孟臣，李敏，串行接口键盘控制器 SK5278 及其在单片机系统中的应用J，国外电子元器件，2003，(9)：29-31. 15 陈光东，赵性初，单片微型机算机原理与接口技术M，华中科技大学出版社，2001. 16 司立众，鞠全勇，刘旭明，郑李明，轴快流 CO2 激光器谐振腔结构架一种P，2015.7.917 司立众，分立供气轴快流 CO2 激光器占空比配气技术J，制造技术与机床，208 张育川，我国激光产业十年，激光与红外J，2000，30(3)：136-140.毕 业 设 计（论文） 开 题 报 告 2本课题要研究或解决的问题和拟采用的研究手段（途径）： 以单片机为核心的轴快流 CO2 激光器控制面板系统设计方案大体上分为如下几个步骤 ：（1）分析评估控制任务 （2） 单片机的选型 （3） 硬件电路设计 （4） 软件设计 （5）系统的调试与实验 由于激光器安全性要求高，本课题的关键技术是保证面板控制系统的可靠性、稳定性及智能化，并能很好地与下位机紧密配合， 可监视和控制激光器进行正常运行。 1、系统应采取自检措施，能及时发现故障。 2、系统应便于携带，操作简单，修改维护方便。 3、采用简化电路，不进行扩展接口电路，减少不必要的元件。 4、软件的设计上应采用自锁、自检等技术、使之具有高度可靠性。毕 业 设 计（论文） 开 题 报 告 指导教师意见：1对“文献综述”的评语：该生通过大量搜集和查阅文献资料，对与“轴快流 CO2 激光器”相关的国内外前人工作较好地进行了综合分析和归纳整理，具体阐述了轴快流 CO2 激光器工作原理、激光加工产业发展状况等，并对国内外激光器制造技术与激光加工工艺技术进行了概述。从“文献综述”全文来看，达到了学校对“文献综述”的要求。 2对本课题的深度、广度及工作量的意见和对设计（论文）结果的预测：该生对于所开课题进行了较为详尽的市场调研，参考了一定数量的文献资料，最后确定的课题对轴快流 CO2 激光器具有一定的参考和应用价值。本课题是学生所学专业知识的延续，符合学生专业发展方向，对于提高学生的基本知识和技能、提高学生的研究设计能力有一定的锻炼和提升作用。研究目标清晰，研究手段基本合理，工作量适当，难度适中，学生能够在预定时间内完成该课题的设计研究工作。 3.是否同意开题： 同意 不同意指导教师： 2016 年 03 月 03 日所在专业审查意见：同意 负责人： 2016 年 03 月 04 日译文题目： Computational fluid dynamic modeling of gas flow characteristics of the high-power CW CO2 laser To increase the photo electronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.High-power fast axial flow (FAF) CO2 laser is a well-established cutting tool in the manufacturing industry. In large-format laser cutting systems, the laser generally moves with the whole system along the guide rail; there-fore, the structure of the laser has to be as compact and light as possible. The key factor in achieving all these characteristics is to raise the photo electronic conversion efficiency of the single discharge tube. This technology has been under continuous improvement. In the early stage, a single discharge tube of cruciform structure can reach a maximum output of merely 290 W with an optimized entrance nozzle structure. A maximum output of 333 W can be achieved. We recently discovered that the maximum output power of the single discharge tube can reach 500 W. The core theory of this progress is the discharge tube structure and the gas flow field optimization. However, there has been very little domestic research on this subject.Many studies on FAF CO2 lasers have focused on the modeling of laser processes in the laser medium19 . The effects of turbulence flow on the performance of the FAF CO2 laser have also been discussed10 13. These studies have provided good theoretical bases for our re-search. Computational fluid dynamic (CFD) method has become a powerful approach to analyze the three-dimensional (3D) flow in complicated domains. We can make use of previous researches and the CFD method to obtain further insight on the realistic gas flow of the laser and make the design more efficient.In our earlier letter14, we presented a preliminary at-tempt on numerical investigation of a FAF CO2 laser using CFD method, and the results were encouraging. However, much improvement is needed before the actual application. Our previous work simplified the discharge cavity into a straight tube. With the further demand for laser researches and a more accurate grasp of the internal flow field, we established a realistic 3D discharge tube model, including the turbulence generator and the anode and cathode area. In our previous work, the effect of the external electric field was only described via a given constant value, which was equal to the difference between the input electric and laser output power. This approach was not sufficiently accurate because the electric field effects on particular regions inside the laser cavity are different. The contribution of electrons of vibrational states and relaxation of electrons from the asymmetric stretch vibrational levels of CO2 to the ground level also need to be considered15. In this letter, we divide the computational grid into four regions, and then set the source term.An overall view of the grids used in the computations is shown in Fig. 1. The size of the grid is approximately 129184 cells. From Fig. 1, the turbulence generator is constituted by a cylindrical annular cavity located out-side the ellipsoid chamber with a gas inflow opening. The jet orifice connecting the cylindrical annular cavity and ellipsoid chamber is opposite the initial gas inlet and 45 away from the axial. The electrode pin is coaxially disposed with the axis of the jet orifice. This structure helps generate a vortex street and a high-turbulence gas flow, according to the following numerical investigations.The model consists of a set of differential equations for numerical solution of discharge process of the FAF CO2 laser. Before introducing the governing equations, we discuss the division of the computational grids, which is the main improvement from our previous work. The gases in the region of fluid inlet and the cylindrical annular cavity have not been excited; in other words, the effect of the electric field and electric cur-rent need not take the energy conservation equation into account. We define this region as inflow area. The region of intense electrical heating near anode pin is the ellipsoid chamber. We define this region as the an-ode area. The region inside the cylinder of the radius 19.15 mm between the axial distances of 20.42 and 216.3 mm is defined as the positive column area. The axial distance between 216.3 and 224.3 mm is defined as the cathode area. The related source terms will be set into the four areas.CFD method is the numerical simulation of flow under the control of the basic flow equation (conservation of mass, momentum, and energy equations). In this letter,the conservation equations of mass and momentum for the gas flow in the discharge tube are the same as the non-ionized gas if the contribution of the electric force is ignored.However, the energy equation should consider the contribution of electron of vibrational states,relaxation of electrons from the asymmetric stretch vibrational levels of CO2 to the ground level, and electrical heating. We are interested in the small-signal gain; therefore, the intensity Iv inside the cavity is assumed to be 0. The distributions of the internal flow fields in the discharge tube are considered as in steady-state; thus,we can neglect time-term in governing equations. The governing equations of the dynamic process in the laser cavity can be written as5,6,8where is the gas density; ui are the components of the gas velocity (i=x y, z ); xi are the space coordinates;P is the gas pressure;f =0.3164Re 1/4 is the friction coefficient, where Re = (u/)dr is the Reynolds number, is the viscosity of the gas, and dr is the discharge tube diameter4;is the diffusion coefficient, which will be defined and discussed later; ij are the elements of the stress tensor; ne is the electron density; h is the value of the Planck constant; nCO2 and nN2 are the concentrations of the molecules of CO2 and N2; v3 and v4 are the frequency of the first excited state of the asymmetrical stretch mode and frequency spacing between the N2 vibrational levels; 3 and 4 are the excitation rates of the asymmetric stretch mode of CO2 and of the vibrational mode of N2 , respectively; h3 is the specific vibrational energy of the asymmetric stretch mode of CO2 (we assume that the stimulated emission occurs only for 10P (20) transitions in the (0001, J ) (1000,J +1) band); 3 is the relaxation time of energy transfer from the CO2 asymmetric mode to the combined CO2 bending and symmetric stretch mode; I is the electric current, E is the electric field intensity, and I E is the electrical heating of the gas5,8.After the computational grids have been established and the conservation equations of mass, momentum, and energy have been presented and discussed, the next step is to import the grid into FLUENT software. FLUENT software only contains the basic flow equations; therefore, the contribution of the electric field effect added in the energy equation will be loaded as user-defined functions according to the write programs. The CFD solving process in FLUENT software has been shown in our earlier letter14.The boundary and initial conditions are key parts of the computational procedure because they are the prerequisites of the correct solutions of the governing equations. For the compressible turbulent flow model, the gas inlet and gas outlet adopted the pressure inlet and the pressure outlet boundary conditions, respectively. The initial conditions included the gas inlet and outlet pressure, temperature, and many other dynamic parameters.The inlet temperature was assumed to be equal to room temperature 293 K. The outlet temperature was 421 K,which was measured in the experiment. Therefore, the qualitative temperature which was the mean value of the inlet and outlet temperatures was expected to be 357 K.This temperature was used for the estimation of the material parameters, which had to be defined before18 starting iteration. The input parameters of the model are shown in Table 1.As shown in Figs. 2 and 3, the gas pressure and density of the laser cavity are calculated versus tube length at 3 mm (plots A) away from the central longitudinal line of the laser cavity, the center line (plots B), and at 3 mm (plots C) away from the center line. Since the inlet opening is located at 51-mm radius from the laser axis,the pressure and density variation in the region of the inflow area cannot be presented in the two figures. However, the positive column region is the main part that reflects the discharge process in the laser cavity. Therefore, we select the three given lines as representative explanations. The zero-point in the x-axis is opposite the center of the jet orifice connecting the cylindrical annular cavity and ellipsoid chamber. Apart from the small region near the entrance of the tube, the gas pres-sure and density variations do not exceed 10%, and are only slightly dependent on the distance from the axis. At the fore part, the significant decrease is mainly due to the gas mixture introduced in the tube through the narrow orifice to the ellipsoid chamber. The dimension of the flow section suddenly increases. This is related to the decrease of the radius of the laser cavity.Fig. 1. General view of the grids used in our computations.Table 1. Initial Input Parameters of the Computational ModelMixing Gas Notation ValueTube Length L (mm ) 274.1Tube Diameter D (mm) 19.15Average Molecular M (kg/mol) 12.28WeightThermal Conductivity k W/(m K) 0.0943Viscosity kg/(m s) 2.313105Heat Capacity atcp J/(kgK) 1943Constant PressureInlet Gas Pressure P (Pa) 18400Outlet Gas Pressure P (Pa) 10400Inlet Gas Temperature Ti (K) 293Outlet Gas Temperature To (K) 421The gas velocity nephogram in the central longitudinal section of the laser cavity is shown in Fig. 4. Since the anode pin is placed opposite the initial gas inlet and 45 away from the axial, the anode pin and jet orifice cannot be seen in this figure. According to the fluid dynamic theory, the input flow blows through the narrow orifiyce with a cross-section several times smaller than that of the discharge tube. Thus, the input gas flow is near sonic, highly turbulent, and has a distinct turbulent core near the entrance. The computational result shown in Fig. 4 justifies the above analyses. The turbulent core is in the center of the ellipsoid chamber. The distributions of the gas velocity in the inflow and anode regions are non-uniform because of the high turbulent from the cylindrical annular cavity and nozzle. The above distributions are not shown in our previous work. After the anode region, the gas velocity and its distribution stability increase along the discharge tube length, especially downstream of the positive column region, which is the main area determining discharge stability. This is the global distribution showing the overall distribution trends of the gas velocity. To obtain the detailed distribution of the gas velocity, the following analysis is needed.Fig. 2. Plots of the gas pressure versus tube length at 3-mm radial distance (curve A), at the center line (curve B), and at 3-mm radial distance (curve C) of the discharge tube.Fig. 3. Gas density versus tube length.Fig. 4. Contours of velocity distribution inside the laser cavity.The plots of the axial velocity versus axial length under the inlet openings are shown in Fig. 5. The selection of the curves is similar to that in Fig. 2. From Fig. 5, the largest axial velocity is at the zero-point, which is the center of the nozzle. The sharp drop after the zero-point is due to the introduction of the gas mixture in the tube through the narrow orifice to the ellipsoid chamber and the sudden increase in the dimension of the flow section. The initial increase after the sharp drop of this velocity is related to the decrease of the radius of the laser cavity. The increase is related to the decrease of the plasma density (see Fig. 3) which is caused by the increase of the temperature heated by the gas discharge. The decrease beyond the cathode is related to the increase of the radius of the laser cavity. In the region of 25 220 mm, the increase of gas velocity is nearly linear, and the differences among curves A, B, and C are negligible. Therefore, the gas velocity distribution is uniform.Previous studies have demonstrated that high veloc-ity is helpful in the timely removal of the heat from discharge and in obtaining high efficiency. However, in the optimization process, even if the gas velocity is high, the gas discharge appears jittery, and the electrical power cannot be injected when the excitation current increases to a certain extent. The unreasonably designed discharge tubes cannot obtain uniform distribution of the gas velocity. Therefore, the uniform distribution of gas velocity is an important prerequisite for increasing the output power.The effect of gas flow turbulence on laser output has been investigated in the previous research; results showed that gas flow turbulence was important for increasing laser power4. However, a highly turbulent flow also means a large instability factor in the gas flow. More-over, an unstable distribution of the turbulent intensity will cause severe local heating of the gas, with increase in current intensity. This makes the light area constrict to the tube center where the turbulent intensity is weak, and causes the necking phenomenon of the plasma. There-fore, a stable distribution of turbulent intensity at the discharge tube center is an important prerequisite for a uniform and stable glow discharge. The turbulent intensity distributions need to be calculated and displayed. Figure 6 shows the turbulence intensity versus the tube diameter at 50 mm (curve A), 100 mm (curve B), and 150 mm (curve C) away from the initial gas inlet of the laser tube. From this figure, near the entry of the laser cavity, the highly turbulent flow is generated by the en-trance structure to increase the probability of particles collision. The turbulent intensity is high, but unstable. When the gas flow tends towards stability along the tube length, the turbulence intensity also tends to stabilize.Fig. 5. Gas velocity versus tube length.Fig. 6. Plots of the turbulence intensity versus tube diameter at 50 (curve A), 100 (curve B), and 150 mm (curve C) axial length of the discharge tube.The turbulence intensity decreases along the tube length; however, the stability increases. At 150 mm away from the initial gas inlet, the distribution of the turbulence intensity is nearly symmetrical, and the value change is minimal in the region of 66 mm, which represents that the distribution of turbulence intensity is nearly stable in the tube center.Our experiments were carried out on a DC excited FAF CO2 laser developed in our institute using nominal output power of 4 kW. Actual measurement of the internal flow field of the laser cavity is difficult; thus, we determined its dimension by observing whether there was discharge channel jitter with the increase in excitation current. Discharge tubes with external circumferential flow structure were applied in the laser. The excitation current then gradually increased to observe the discharge process under different injection electric powers. The tube can maintain a stable glow discharge when the ex-citation current increased from 45 to 85 ma. According to the observation, the gas flow pattern is as stable as the computation results (Figs. 5 and 6).Comparison of the computational results and the experimental value of the gas flow characteristics are given in Table 2. There is a good agreement between the computation and experiment. Although slight differences exist, results are not affected.In conclusion, the turbulence flow in the optimized discharge tube has been numerically investigated by CFD method to provide a simulation and optimum design criteria for high-power FAF CO2 laser. The complete structure 3D model and the partial loading source terms have allowed us to describe more accurate details of the internal gas flow field distribution. Results have shown that uniform axial gas velocity and stable radial turbulence are necessary to ensure a uniform and stable glow discharge, which is an important prerequisite in increasing the photo electronic conversion efficiency of the single discharge tube. Results of computations have been shown to be in reasonable agreement with the experimental observations.Table 2. Computational Results and Experimental Values of the Gas Flow CharacteristicsGas Flow Computational ExperimentalCharacteristics Results ValuesInlet Mass Flow-Rate (kg/s) 0.00279 0.00285Outlet Temperature (K) 430 421Pressure Loss (Pa) 796 800Output Power
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