基于Fluent模拟分析的真空下液体射流喷嘴的选型

本文以真空喷射法制备聚合物薄膜为研究背景,对其重要的发生元件喷嘴进行了选型研究.现阶段应用最为广泛的直射式喷嘴有直线型、锥形、锥直型和抛物线型四种类型,通过Fluent软件对喷嘴喷射后的液体射流流速、压力分布和湍流强度三个方面进行了模拟分析.结果表明:在相同的初始条件下,锥形直射式喷嘴其射流速度分布均匀,压力分布也比较均匀,射流流场的扩散性优于其它类型的喷嘴;此外其射流雾化后的液滴尺寸分布均匀,射流的贯穿距离较长,液体出喷嘴后湍流强度较大,射流后液体的雾化破碎效果较好,更适于制备成膜致密,膜厚均匀可控的聚合物薄膜.     

喷嘴结构对真空喷射雾化性能影响研究

基于Fluent软件模拟了柱型、扇型、锥型和混合型喷嘴真空喷射射流雾化过程,研究了喷嘴结构对动压力转换、射流速度和喷嘴出口湍动能的影响。结果表明,锥型喷嘴动压力较大,可提高静压能转换效率;扇型和锥型喷嘴喷射束宽度较大,利于大面积喷射成膜;扇型喷嘴易形成空化,出口湍动能较大,有助于液滴初次雾化破碎,而混合型喷嘴的空化层厚度最小,湍流区域最大。通过分析雾化锥角与喷嘴流量系数,发现扇形和锥直形喷嘴具有较大雾化锥角,但流量系数较小喷嘴压力损失较大;喷嘴直线段会提高锥型喷嘴雾化锥角和喷嘴出口湍动能,并使扇型喷嘴的流量系数增大,但射流雾化锥角减小。最后,本文尝试构建了真空喷射射流雾化数学模型。     

突扩膨胀射流冲击换热与流动的数值模拟

采用大涡模拟模型对突扩膨胀射流冲击平板的传热特性及喷嘴内部流场进行数值模拟,得到不同进口Re数,不同膨胀比情况下喷嘴内部流场和射流冲击平板时的换热效果,分析了不同进口Re数、膨胀比E、冲击高度H/d对换热和流动的影响.研究表明,与直喷嘴进行对比,由于膨胀喷嘴射流与周围介质的掺混、渗透作用使射流的流速大大降低,最大速度偏离几何中心,使得换热效果减弱,对加热平板的冷却具有不对称性,但使得整个换热板的平均冷却效果更加均匀.     

微射流抛光机理仿真及实验研究

为实现193 nm投影物镜光学元件的超光滑加工,介绍了一种非接触式微射流超光滑表面加工方法,对该方法的材料去除特性和超光滑加工效果进行研究.首先,采用计算流体动力学理论对其材料去除机理进行了仿真研究,通过对微射流流场的压力、速度和表面剪切力的分析得到其去除函数形状与表面剪切力的分布相反,呈现W型.随后,采用正交法对各工艺参数对抛光效果的影响进行了综合分析,结果表明材料去除效率随入射速度和磨料浓度的增大而增大,随工作距离增大而减小,并且工作距离具有显著影响,为实验研究中工艺参数的选取提供了指导意义.最后,在自研的微射流抛光机床上对一平面熔石英进行了抛光实验,加工样件表面粗糙度均方根值由初始的1.02 nm降为0.56 nm.实验结果表明,微射流抛光技术可以用于光学元件的超光滑加工.     

电弧加热器流场数值模拟研究

电弧加热器流场特性是影响材料热化学烧蚀的关键因素之一,根据可压缩的轴对称N-S方程,对喷嘴的超声速自由射流、垂直冲击射流进行了数值模拟,采用k-ε湍流模型.计算得到自由射流流场结构的三个区域:射流核心区、射流卷吸区和射流湍流区,射流的速度分布具有不均匀性,其轴线射流速度存在较大变动;冲击射流近壁处存在着滞止区.所获得的喷嘴外部流场的流动状况以及冲击射流参数分布,如压力、温度和速度分布,可用于烧蚀试验和计算优化设计,流场计算结果与烧蚀实验值吻合.     

高背压下平口喷嘴射流锥角影响因素分析

高背压下条件下的射流在火电的减温水喷射、燃气轮机、加压煤气化、潜艇等领域具有广泛的应用。由于高背压射流参数计算方法缺失,本文利用搭建的高背压实验系统,选取8种不同结构参数的喷嘴进行实验,研究背压、喷射压差、喷嘴长径比等参数对射流锥角的影响。分析实验结果,发现背压对射流锥角影响较大,在高背压时,背压越高,射流锥角越大;在低背压时,射流锥角受喷嘴内部流动状态影响较大,低背压时,喷嘴内部易产生空穴流动,空穴的产生促进射流锥角的增大,其影响不可忽略。     

真空喷射雾化过程中喷嘴口的流动模型计算与数值分析

在真空喷射法制备薄膜的过程中,射流效果如何主要取决于喷嘴的结构。不同的喷嘴对液体射流雾化的影响不同,其作用效果主要取决于喷嘴中喷口的形状,通过对三种不同喷嘴喷口形状的流动模型的建立和数值分析可知锥直型喷口其水蒸气的体积分数变化较小,雾化效果最好且成膜的质量最高。     

印刷涂布烘箱V型条缝喷嘴冲击射流流场的数值模拟

为了解印刷涂布设备烘箱V型条缝喷嘴冲击射流流场分布及其影响因素,采用标准k-ε湍流模型,对喷嘴射流冲击移动壁面进行数值模拟。分析了喷嘴冲击射流壁面附近速度场和压力场分布情况,考虑了影响喷嘴冲击射流壁面附近速度分布的喷嘴宽度和高度等因素。研究结果表明:在冲击射流中,喷嘴距壁面的高度和喷嘴宽度对壁面附近速度分布影响较为明显;综合考虑各种因素,较理想的喷嘴高度是15 mm,相应的喷嘴宽度为2.5 mm。     

旋进射流喷嘴的频率及流场特性研究

在圆筒套管内设置一块孔板构成旋进射流喷嘴，由此获得持续稳定的旋进射流，研究了喷嘴最优的结构参数。用热线风速仪测量出口射流的速度并进行功率谱分析，得到旋进射流的频率及流场特性。研究表明，旋进射流具有较高的紊流强度，速度场沿径向的分布趋向平缓，其进动频率随流量增大而加快，喷嘴的尺寸和结构对射流进动有影响。     

光学加工中抛光垫特征对工件面形的影响分析

抛光是光学加工中获得超精密表面的主要手段.为明确抛光垫特征对平面光学元件抛光面形的影响规律,分析了抛光垫与工件之间的界面接触形式,并建立接触力学分析模型,运用有限元方法分析了工件与抛光垫之间的接触压力分布情况,获得了抛光垫厚度及表面球半径等特征对抛光压力分布的影响规律.基于理论分析结果,提出了一种新的平面抛光面形控制技术.在实验中对一块尺寸为430 mm×430 mm×60 mm的熔石英元件进行了加工,通过将抛光垫表面修整为微凸面,同时对抛光转速比进行精确控制,实现了工件面形精度的快速收敛.     

The application of hybrid RANS/ILES approach for the investigation of the effect of nozzle geometry and mode of efflux on the characteristics of turbulence of exhaust jets

The efficient hybrid RANS/ILES approach is used for the investigation of the effect of nozzle geometry and parameters of flow at the nozzle exit section on the characteristics of turbulence in the exhaust jet. The calculations are performed for nozzles of different types such as conical and chevron nozzles and the nozzle of double-flow turbojet engine (TJE) with chevrons on the core nozzle. The effect of the foregoing parameters on the level of fluctuations of velocity and pressure in the investigated jets is demonstrated. The effect of off-design mode of efflux on the parameters of turbulence in the jet is investigated under conditions of supersonic efflux of the jet. The effect of misalignment of the core and fan nozzles on the flow in the jet is considered for the nozzle of double-flow TJE. Grids containing about 10⁶ cells are used for the calculations. The accuracy of the results is confirmed by comparison with the known experimental data.     

双腔室自激振荡喷嘴频率特性研究

摘要：作为对双腔室自激振荡喷嘴这一新型喷嘴的探索,基于流体网络理论建立了双腔室自激振荡脉冲射流喷嘴的相似网络模型,理论分析了双腔室自激振荡喷嘴频率特性。模型计算结果表明：双腔室自激振荡喷嘴结构参数对系统的固有频率有重要的影响,系统结构参数间存在最优匹配关系,并与文献中介绍的单腔室结构参数的最佳配比关系有较大的不同,双腔室自激振荡喷嘴较单腔室自激振荡喷嘴可以提高脉冲射流峰值压力。分析结果对双腔室自激振荡喷嘴结构设计具有一定的借鉴价值。     

Performance Comparison of Four Waterjet Nozzles

This article presents the results of laboratory tests on four waterjet-cleaning nozzles for industrial use. The nozzles selected for the tests included standard cone-jet and fan-jet nozzles, a cavitating jet nozzle and a resonating jet nozzle. A series of cleaning and erosion tests were conducted to compare the performance of the nozzles in terms of erosion rates and jet coverage, based on the same amount of energy input. The fan-jet nozzle was extremely sensitive to small variations in standoff distance. The cavitating jet nozzle gave similar performance over a large range in standoff distance. The cavitating jet and fan-jet nozzles were more efficient at an angle of incidence of 0° and 40°, respectively. For the same settings, the cone-jet and resonating jet nozzles gave an overall poorer performance than the fan-jet and cavitating jet nozzles. The cavitating jet nozzle exhibited even better erosion rate, erosion depth, and footprint covered than the fan-jet nozzle.     

Numerical study of liquid nitrogen cavitating flow through nozzles of various shapes

The cavitating flow of cryogenic liquid through a spray nozzle is influenced by many factors, such as unique thermophysical properties of cryogenic liquid, the inflow temperature and the complicated geometrical structure of the spray nozzle. The geometrical parameters of liquid nitrogen spray nozzles have a profound impact on cavitating flow which in turn affects spray atomization characteristics and cooling performance. In present study, CFD simulations are performed to investigate influence of the nozzle geometry on the liquid nitrogen cavitating flow. The mixture model is used to describe the liquid-vapor two phase flow, and both the cavitation and evaporation are considered for the phase change. The predictions of mass flow of liquid nitrogen spray are validated against experimental results. The effects of geometric parameters, including the outlet orifice diameter and the length of nozzle, the inlet edge angle of orifice, the inlet corner radius of orifice, the orifice shape and different positions of swirl vanes, are investigated under a wide range of pressure difference and inflow temperature. The results show that the effects of geometric parameters on cavitating flow show different trends under subcooled conditions compared with saturated temperature conditions. The flow characteristics are more affected by the changes of the inlet edge angle, the inlet corner radius, and the orifice shape. The insert of swirl vanes has an effect on the distribution of the cavitated vapor within the orifice, but it has little influence on flow characteristics. The results could enrich our knowledge of liquid nitrogen cavitating flow in spray nozzles of various shapes.     

Influence of nozzle vibrations on the aerodynamic characteristics of a jet

The results of investigations of the aerodynamic characteristics of turbulent jets issuing from nozzles and subjected to the action of various kinds of low-frequency vibrations — transverse, longitudinal, and torsional (during axisymmetric vibrations of the nozzle around the longitudinal axis) — are presented. Data on the laws governing changes in the average and pulsation velocities along the jet axis, as well as on the spectra of velocity pulsations in the zone of jet mixing, have been obtained. It has been established that at low-frequency vibrations of the nozzle a noticeable intensification of jet mixing is attained. The same effects as on acoustic excitation of a jet are observed. The experiments were carried out at Reynolds numbers Re = 2∙10⁴–8∙10⁴.     

Experimental and numerical simulation of the flow in a driving module with an annular and linear double-slot nozzle

This paper presents the results of numerical and experimental studies of the flow and comparison of propulsion performance characteristics of a model of a jet engine exhaust system equipped with an annular or (equivalent in gas consumption) linear double-slot nozzle with an inner cavity and circular segment deflector in the axial section. Calculations performed for the annular nozzle and double-slot nozzle corresponding to it in geometric parameters demonstrate that a flow similar to the flow in nozzles with a central body is formed in the exhaust system. According to the data obtained, the initial turn of the flow takes place in the oblique shock wave. In the double-slot nozzle, the final turn of the flow in the direction of the thrust vector occurs in a configuration of four shock waves positioned downwards in the flow; in the annular nozzle, it is in the intense barrel shock wave. It was established that the exhaust system with an annular of the linear doubleslot nozzle develops a thrust and specific impulse that exceed the corresponding values for the sonic nozzle equivalent in gas consumption by almost a factor of 2.     

Mixing enhancement using chevron nozzle: studies on free jets and confined jets

This paper reports an experimental study focused on the impact of chevrons (serrations on the trailing edge of the nozzle) on the mixing process of an incompressible jet issuing from a convergent nozzle. The study also explores enhancement of the mixing performance by a novel approach to geometry modification. Profiles of mean velocity were used to characterize the extent of mixing. For a comparative assessment, studies were carried out with a base line circular nozzle, a conventional chevron nozzle and an improvised tabbed chevron nozzle. Flow visualization studies were carried out for jets issuing from chevron nozzles and the results corroborate well with quantitative measurements. The impact of confinement on mixing of jets issuing from chevron nozzles is also studied. The results show that the proposed geometry modification can significantly improve the rate of mixing in the range of Reynolds numbers considered in the study. In confined jets, presence of chevrons was found to accelerate the process of jet break-down.     

包装印刷设备的烘干风嘴分布参数规律研究

目的为了提升包装印刷设备烘干性能,针对风嘴分布进行研究。方法依据实际包装印刷设备风嘴为参考,建立风嘴分布模型并进行非结构网格划分,根据实际情况建立适用于其工况的边界条件和控制方程;控制风嘴间距和承印物距离这2个关键参数,建立风嘴分布参数与热风场性能之间的数学模型;依据所建立数学模型估算不同参数模型的烘干效果。结果根据多组仿真实验得到了风嘴间距和承印物距离等参数对热风场分布的影响,相应经验公式为v (=-0.007×L+2.568)x~(4.311/L+0.056)。风嘴间距对于烘干风嘴影响效果明显,增加风嘴间距离可以提升烘干风嘴风速和热风场的均匀性;同时发现随着承印物不断前进和风嘴作用效果的叠加,其表面风速将持续呈现上升。结论经过研究分析,掌握了不同参数下的热风场分布规律,这对指导实际生产对于烘干风嘴设计具有重要参考价值。