Tomographic particle image velocimetry measurement on three-dimensional swirling flow in dual-stage counter-rotating swirler

Three-Dimensional(3D)swirling flow structures,generated by a counter-rotating dualstage swirler in a confined chamber with a confinement ratio of 1.53,were experimentally investigated at Re=2.3×10^(5)using Tomographic Particle Image Velocimetry(Tomo-PIV)and planar Particle Image Velocimetry(PIV).Based on the analysis of the 3D time-averaged swirling flow structures and 3D Proper Orthogonal Decomposition(POD)of the Tomo-PIV data,typical coherent flow structures,including the Corner Recirculation Zone(CRZ),Central Recirculation Zone(CTRZ),and Lip Recirculation Zone(LRZ),were extracted.The counter-rotating dual-stage swirler with a Venturi flare generates the independence process of vortex breakdown from the main stage and pilot stage,leading to the formation of an LRZ and a smaller CTRZ near the nozzle outlet.The confinement squeezes the CRZ to the corner and causes a reverse rotation flow to limit the shape of the CTRZ.A large-scale flow structure caused by the main stage features an explosive breakup,flapping,and Precessing Vortex Core(PVC).The explosive breakup mode dominates the swirling flow structures owing to the expansion and construction of the main jet,whereas the flapping mode is related to the wake perturbation.Confinement limits the expansion of PVC and causes it to contract after the impacting area.

Robust lag synchronization between two different chaotic systems via dual-stage impulsive control

In this paper, an improved impulsive lag synchronization scheme for different chaotic systems with parametric uncertainties is proposed. Based on the new definition of synchronization with error bound and a novel impulsive control scheme （the so-called dual-stage impulsive control）, some new and less conservative sufficient conditions are established to guarantee that the error dynamics can converge to a predetermined level, which is more reasonable and rigorous than the existing results. In particular, some simpler and more convenient conditions are derived by taking the same impulsive distances and control gains. Finally, some numerical simulations for the Lorenz system and the Chen system are given to demonstrate the effectiveness and feasibility of the proposed method.

Design and Experiment of Vertical Motion Dual-stage with Piezo-actuated Nanopositioning Stage

Nanopositioning stage based on piezoelectric(PZT)actuators and flexure mechanisms has been widely used in dual-stage.Its favorable positioning accuracy and dynamic response can guarantee the high performance of the dual-stage.Here the vertical axis motion dual-stage is designed with piezoelectric actuator for the fine-stage and ball-screw drive integrated with wedge sliding mechanisms for the coarse-stage.The aim of the dual-stage is to meet the stringent requirement of scanning over a relative large range with high accuracy.The design results of the piezo-actuated nanopositioning stage show good static and dynamic performance,validated by the simulation of finite element analysis(FEA).Hysteresis nonlinearity due to the use of piezoelectric stacks for actuation is studied and compensated by aproportional-integral(PI)feedback controller.To qualify the design of the motion ranges and resolutions,an experiment platform is established.The experimental results show that the proposed dual-stage has a full range of 12 mm with the resolution of 40 nm.Guideline is provided for the design methodology of the vertical motion dual-range stages.

Implementation of Mooring Automatic Positioning System for Deepwater Semi-Submersible Platform Based on Dual-Stage Actuator

The automatic positioning control of mooring system for deepwater semi-submersible platform has become a key issue in the research and development field of deep-sea resources. The Dual- Stage Actuator (DSA) proposed in this paper can replace the single actuator to achieve the high speed and high precision positioning by cooperative control. The relative model and control algorithm of motion trajectory (CAMT) are designed and validated, which proves that the method proposed in this paper is effective.

双旋流燃烧室冷态流场2维湍流特性试验

为研究燃烧室流场湍流结构特性,采用粒子图像测速仪(PIV)对双级旋流器燃烧室流场进行测量,得到了不同进气速度下的速度场分布、雷诺应力分布和湍流度分布。结果表明:随着进气速度的提高,旋流器出口射流速度提高,中心回流区轴向速度变化较小;在2维平面上,燃烧室轴向测量截面出现5个高雷诺应力区域,分别为中心回流区外、中心回流区与高速旋转射流交汇区(剪切层)2处以及高速旋转射流与燃烧室头部模拟壁面接触区2处;回流区与高速旋转射流交汇区较高的雷诺应力分布有利于燃料与空气充分混合;湍流度分布与速度波动幅值和平均流速有关,中心回流区与高速旋转射流交汇区处湍流度较高。

反向和同向旋流滑动弧等离子体点火助燃头部的燃烧特性

非平衡态等离子体点火助燃技术是新型的燃烧调控技术.面对航空发动机燃烧室稳定燃烧的迫切需求,为发挥滑动弧等离子体技术在改善雾化、提高燃烧效率等方面的优势,搭建了航空发动机燃烧室实验平台,并开展了不同旋流方向下滑动弧放电等离子体的燃烧特性实验.实验通过采集燃烧过程OH^(*)化学发光强度图像,着重分析了不同旋流方向滑动弧等离子体对燃烧室燃烧强度、温度分布以及燃烧效率的影响.研究表明,施加等离子体助燃后,燃烧室内的平均已燃区相对强度明显提升,且反向旋流等离子体助燃的提升效果更加明显;反向旋流滑动弧助燃的径向温度分布相较于同向旋流滑动弧助燃均匀性提升,当余气系数为2.0时,反向旋流等离子体助燃的径向温度分布系数为0.3022,同向旋流等离子体助燃的径向温度分布系数为0.3223;反向旋流滑动弧助燃的燃烧效率高于同向旋流滑动弧放电的燃烧效率,当余气系数为2.0时,反向旋流等离子体助燃的燃烧效率为89.56%,同向旋流等离子体助燃的燃烧效率为83.41%.

Sensitivity analysis of the vane length and passage width for a radial type swirler employed in a triple swirler configuration

The design of axial or radial swirlers typically governs a number of geometrical parameters that are determined by the desired flow field.In the meantime,the number of unknown parameters increases with the number of concentrically mounted swirlers.The available literature is nonetheless limited,and designers are obligated to increase the number of initial assumptions.In this article,three kinds of triple swirlers are employed and simulations are performed to determine the effect of each parameter on the swirler performance.Based on the correlation provided,overlengthening the radial vane length could result in significant changes in the flow field from the jetlike pattern to a wide swirl-jet angle due to the Coanda effect.Passage width should also have the potential to alter the swirl-jet angle and velocity field at the exit of the swirler.

Investigation and Analysis of High Temperature Corrosion and Degradation of Marine Boiler Combustion Swirler

现在的纸调查了并且分析了 swirler 材料由在 30 MW 水兵锅炉为一年的时期受到服务的低碳钢组成。由于在结合的炉子的高温度的存在，腐蚀剂水兵环境 swirler 材料显示出加速的降级和材料消耗量。调查进与交替的材料或涂层生产存在 swirler 的可行性有热障碍涂层的 swirler 材料被承担。基于他们的性质和表演， SS 304 和 SS 316 为 swirler 作为代替材料被建议。有在提高的温度在他们的表演为任何改进观察的热障碍涂层也是的一种形式的存在 swirlers 测试了的涂层的另外的选择。钨铬钴合金，它是一个 Ni 公司基于涂层，在 MS 样品上被执行，一样暴露于上面提及的一样的温度。可得到的选择的表演关于材料的谷物结构被评估，在提高的温度的材料和恶化的坚硬价值。调查证明象 SS 304， SS 316 和钨铬钴合金涂层一样的建议材料 / 涂层表明 SS 316 是适合高温度申请的材料最好。

基于PIV的中心分级燃烧室冷态流场试验

为了掌握中心分级燃烧室流场特性,利用粒子图像测速仪(PIV)对中心分级燃烧室的冷态流场进行试验,对具有不同流通面积的主模旋流器和副模旋流器出口流场进行了对比。结果表明:在压降相同条件下,副模旋流器单独工作时流过的空气流量约占主、副膜旋流器同时工作时的1/3;副模单独工作时,流场中无明显回流区,这表明副模旋流器主要作用是在燃烧室头部提供高速气流与燃油喷嘴喷出油雾颗粒充分混合形成油气混合物;在压降不变的条件下,随着主模旋流器流通面积的增加,空气流量增大,燃烧室头部流场分布受流通面积影响显著;在流通面积不变的条件下,随着供气压降的提高,空气流量增大,流场中旋转回流区位置向燃烧室头部方向移动,面积减小,中心回流区位置基本不变,回流速度加快。

轴向双级反旋预混喷嘴燃烧调整边界实验研究

干式低污染燃烧室为保证安全、稳定、高效的运行状态,通常需要进行燃烧调整。本文针对一种干式低污染燃烧室用轴向双级反旋预混喷嘴,在常温常压条件下开展燃烧调整边界实验研究。测量并探究了影响燃烧调整边界的因素,如贫熄火边界、污染物排放边界以及动态压力脉动边界,着重分析了喷嘴内的剪切层稳焰机理以及火焰根部跳动与壁面相干作用导致的热声振荡机理。研究结果表明,由NO_(x)、CO、火焰状态、动态压力脉动和熄火边界共同决定的稳定运行边界在低负荷条件下为当量比0.576~0.714,随着热负荷升高,运行边界有所收窄。对比分析了纯甲烷以及掺50%H2两种燃料的燃烧调整边界,燃料加氢后边界整体向低当量比移动,运行窗口宽度得到拓展。

主燃级旋流器对中心分级燃烧室出口性能的影响

针对中心分级燃烧室头部主燃级旋流器的结构参数变化,探究其对燃烧室出口性能的影响。首先建立三级旋流器的简化模型,再针对主燃级旋流器的旋流孔角度分别设计30°、45°、60°、75°。利用FLUENT软件对燃烧室沿轴向温度分布、出口温度分布、沿轴向NO_(x)分布、出口NO_(x)排放分布等4个方面进行对比分析。结果表明:当主燃级旋流器旋流孔角度为60°时,旋流器对中心分级燃烧室的出口温度分布性能最好,且中心回流区发展较好,旋流器对中心分级燃烧室的出口NO_(x)排放量最小。

Plasma transport simulation under different conditions and optimization analysis of dual-stage grid ion thruster

In order to study the extraction and acceleration mechanism of the dual-stage grid,a three-dimensional model based on the Particle-In-Cell/Monte Carlo Collision(PIC/MCC)method is performed.Dual-stage grid ion thruster is a new type of electrostatic ion thruster,which can break through the limitations of traditional gridded ion thrusters,and greatly improve the specific impulse.The high performance also makes the grid sensitive to operating parameters.In this paper,the influence of grid parameters on xenon ion thruster’s performance in a wide range is systematically simulated,and the optimal operating condition is given.Both the over-focusing of the plume,and the transparency of the screen grid are improved,and the grid corrosion is reduced through simulation optimization.The specific impulse under the given working conditions is 9877.24 s and the thrust is 7.28 mN.Based on the simulation optimization,the limitation of the dual-stage grid is discussed.The grid performs well under high voltage conditions(>3000 V)but not well under low voltage conditions(<2000 V).Finally,since argon is cheaper and more advantageous in future engineering applications,the plasma distribution and grid extraction ability under xenon and argon are analyzed and compared to study the flexibility of the dual-stage grid ion thruster.The simulation results show that a set of optimal parameters is only applicable to the corresponding propellant,which needs to be optimized for different propellant types.

三头部燃烧室旋转滑动弧点火实验研究

基于燃烧室常用的斜切孔+径向叶片式涡流器,设计并加工了旋转滑动弧涡流器。放电试验表明,旋转滑动弧涡流器可在预定位置产生稳定的旋转滑动弧。在三头部燃烧室试验件上开展了旋转滑动弧点火试验。结果表明,在地面常温、地面低温及3.0km空中环境,相比常规点火,点火油气比下降超过20%;在4.5km空中及5.5km空中环境,点火油气比高于常规点火。低温低压条件下旋转滑动弧放电能量大幅减小。相比环境温度的降低,环境压力的下降对旋转滑动弧的工作影响更大。采用旋转滑动弧点火后,燃烧室的着火时间、联焰时间及点火时间均有缩短。其中,着火时间缩短最为明显,缩短幅度超过60%。联焰时间及点火时间的缩短主要得益于第一阶段着火时间的大幅缩短。

旋流器结构对中心分级燃烧室热态流场的影响

以装有三级斜切式径向旋流器的中心分级燃烧室为研究对象,利用数值模拟和控制变量的方法分别进行了值班级第一级旋流器斜切孔角度、值班级第二级旋流器叶片安装角和主燃级旋流器旋流孔角度对中心分级燃烧室热态流场影响的仿真和对比分析。结果表明:当值班级第一级旋流器斜切孔和值班级第二级旋流器叶片安装角角度分别为25°和30°~45°,主燃级旋流器旋流孔角度为45°~60°时,中心回流区的形状最好,中心分级燃烧室热态流场的品质最佳。

径向旋流器叶片安装角对多旋流分级燃烧室性能影响研究

针对燃气轮机高性能低排放燃烧室的发展需求,提出了一种多旋流组合式头部结构,通过数值模拟的方式研究了径向旋流器叶片安装角对燃烧性能的影响.结果表明:随着径向旋流器叶片安装角增大,旋流器出口燃油与空气混合均匀性提高,回流区轴向尺寸减小,回流区内中轴线湍流强度逐渐增大,出口温度分布系数逐渐降低,燃烧效率与压力损失均呈增大趋势,NO_(x)排放逐渐升高.压力损失y与出口温度分布系数u随叶片安装角x的变化拟合关系式分别为:y=0.0434x+0.207和u=-0.732x+66.64(50≤x≤65).径向旋流器叶片安装角为60°时,燃烧室有较好的综合性能参数.

低排放塔式同轴分级旋流配比对燃烧流场的影响

以天然气-低排放塔式同轴分级燃烧室为研究对象,采用Realizable k-ε湍流模型和FGM燃烧模型研究了旋流器旋流数对热态流场的影响.结果表明:随着二级旋流数增加,中心级和一级流量增加,二级流量减少,燃料掺混均匀性提高,均匀指数最大提高0.061;压力损失小幅增加,而CO排放显著减少,燃烧效率提高且超过99%;模拟的各工况温度分布均匀,均形成稳定的回流区,燃烧稳定;对16种不同的旋流器方案进行筛选,选出0.7/0.8旋流器方案为最佳方案.

旋流器叶片弯曲角度对旋流特性的影响

由于环形燃烧室结构紧凑、空间利用率高,所以在民用航空所使用的涡轮风扇发动机中得到广泛应用。该文建立环形燃烧室的火焰筒和双级旋流器模型,并采用数值模拟的方法对其旋流特性进行分析。旋流器的第一级和第二级叶片分别选取多种安装角度的组合,仿真计算发现,随着安装角度的增大回流区的特征长度增加较为明显,但特征宽度变化不大,这有利于保护壁面避免烧蚀,同时流速小的回流区会使火焰更充分和稳定地燃烧。进一步计算阻力损失系数发现,阻力损失系数随旋流数的增大而增大,这可能是由于旋流数越大,气流撞击叶片发生偏转时损失的能量越大,进而导致阻力损失的增大。因此,在设计旋流器时,不仅要考虑回流特性还需要考虑气流的阻力损失。

旋流器形式对双环腔燃烧室点火性能的试验研究

为了提高双环腔主燃烧室在大流量、宽广工作范围内的贫油点火边界,对值班级单级轴向旋流器及双级径向旋流器两种形式的旋流器进行冷态流场及油雾场的数值模拟和贫油点火的试验研究。结果表明:两种旋流器形式下,流场均为三涡结构。相比值班级为单级轴向旋流器的燃烧室,双级径向旋流器的燃烧室形成的回流区直径大,长度不变,回流强度增大30.6%,燃油浓度增加,贫油点火边界在3个火焰筒压降下变宽40%以上,且均存在最佳火焰筒压降,使得贫油点火边界最宽。

旋流器结构特征参数对中心分级燃烧室温度场的影响

以装有三级旋流器的中心分级燃烧室为研究对象,分别建立旋流器和燃烧室物理模型,利用数值模拟和控制变量的方法,研究旋流器结构特征参数对中心分级燃烧室温度场的影响,分别完成了值班级第一级、第二级旋流器和主燃级旋流器结构参数变化对中心分级燃烧室温度场影响的数值模拟和对比分析。结果表明:当值班级第一级旋流器的斜切孔角度为25°和值班级第二级旋流器的叶片安装角度为30°~45°时,中心回流区分布较好,反映出值班级旋流器对中心分级燃烧室温度场的影响较好,促进了火焰稳定燃烧;当主燃级旋流器旋流孔角度为45°~60°时,中心回流区分布较为理想,反映出主燃级旋流器对中心分级燃烧室温度场的影响较为理想,可有效避免因中心回流区面积过大造成燃烧室高温区集中。

无掺混孔中心分级燃烧室性能数值研究

以一种无掺混孔的中心分级燃烧室为研究对象,通过改变燃烧室中三级旋流器结构参数,利用数值模拟研究旋流器结构对燃烧室性能的影响。首先使用控制变量法,通过改变各级旋流器叶片的安装角大小及旋向设计了研究方案,再通过FLUENT进行数值模拟,最后对数值模拟的结果进行分析并得出结论。结果表明:第一、二级旋流器叶片的结构对燃烧室的回流区大小和出口温度分布影响较小,而第三级旋流器叶片安装角大小对燃烧室的回流区和出口温度分布影响较大;第三级旋流器安装角越大,回流区越大,燃烧就越充分,燃烧室出口温度分布就越均匀。