Design and Atomization Characteristic of Laval-style Annular Slot Nozzle

Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.

The influence of Laval nozzle throat size on supersonic molecular beam injection

In this study, finite element analysis （FEA） has been used to investigate the effects of different Laval nozzle throat sizes on supersonic molecular beam. The simulations indicate the Mach numbers of the molecular stream peak at different positions along the center axis of the beam, which correspond to local minimums of the molecular densities. With the increase of the throat diameter, the first peak of the Mach number increases first and then decreases, while that of the molecular number density increases gradually. Moreover, both first peaks shift progressively away from the throat. At the last part, we discuss the possible applications of our FEA approach to solve some crucial problems met in modern transportations.

Numerical simulation of the dimensional transformation of atomization in a supersonic aerodynamic atomization dust-removing nozzle based on transonic speed compressible flow

To simulate the transonic atomization jet process in Laval nozzles,to test the law of droplet atomization and distribution,to find a method of supersonic atomization for dust-removing nozzles,and to improve nozzle efficiency,the finite element method has been used in this study based on the COMSOL computational fluid dynamics module.The study results showed that the process cannot be realized alone under the two-dimensional axisymmetric,three-dimensional and three-dimensional symmetric models,but it can be calculated with the transformation dimension method,which uses the parameter equations generated from the two-dimensional axisymmetric flow field data of the three-dimensional model.The visualization of this complex process,which is difficult to measure and analyze experimentally,was realized in this study.The physical process,macro phenomena and particle distribution of supersonic atomization are analyzed in combination with this simulation.The rationality of the simulation was verified by experiments.A new method for the study of the atomization process and the exploration of its mechanism in a compressible transonic speed flow field based on the Laval nozzle has been provided,and a numerical platform for the study of supersonic atomization dust removal has been established.

Comparative study on the flow fields of three atomization nozzles

In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.

Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.

Laval喷管中CO_(2)凝结特性数值模拟研究

超临界二氧化碳压缩机是超临界二氧化碳循环的关键核心设备之一,压缩机入口参数接近临界点,叶轮附近的局部加速现象会引发两相区的出现,这可能会对压缩机的安全稳定运行带来隐患。为了深入认识并找出解决该问题的方法,本文将液滴凝结经典成核和生长模型以离散颗粒模型(discrete particle mode,DPM)的形式嵌入流体计算模型,开发出描述超临界二氧化碳凝结的CFD-DPM数值模拟方法,并验证其可靠性。数值模拟结果表明,该方法模拟出的结果与实验数据相符较好。Laval喷管的渐缩部分工质压力急剧降低,达到了很高的过饱和度状态,穿过亚稳态区进入凝结区域,创造极为有利于凝结的环境,因此二氧化碳工质在这个位置集中凝结,即成核率最大的位置出现在x=-0.012 m位置处,最大值约为2.58×10^(25)个/(m^(3)·s)。在二氧化碳凝结的同时,释放出来的热量使工质状态向亚稳态区域偏移,液滴凝结的驱动力减弱,液滴的成核速率和生长速率减缓。本文提出的CFD-DPM方法具有详细描述凝结液滴演化规律的功能,可应用在超临界二氧化碳压缩机的模拟中,有望展示压缩机叶轮进口的凝结液滴的发展演化规律,为高性能超临界二氧化碳压缩机的设计和优化提供高效手段。

PARAMETRIC STUDY ON THE THRUST OF BUBBLY WATER RAMJET WITH A CONVERGING-DIVERGING NOZZLE

To predict the thrust of bubbly water ramjet with a converging-diverging nozzle, the physical processes occurring in the diffuser, mixing chamber and nozzle were analyzed. The mathematical models were constructed separately under the restrictions of certain assumptions. The bubbly nozzle flow was examined using a two-fluid model and accomplished by specifying the water velocity distribution in the nozzle. The numerical analysis of flow field in the nozzle shows that the Mach number at the throat is 1.009, near unity, and supersonic bubble flow appears behind the throat. There is greater thrust produced by bubbly water ramjet, compared with single-phase air ramjets. Subsequently, the influences of vessel velocity, air mass flow rate, inlet area Ai, area ratio （i.e., mixing chamber to inlet area Am/Ai）, and initial bubble radius on the thrust were emphatically investigated. Results indicate that the thrust increases with the increase of air mass flow rate, inlet area and the area ratio, and the decrease of initial bubble radius. However, the thrust weakly depends on the vessel velocity. These analytical and numerical results are useful for further investigation of bubbly water ramjet engine.

不同压力下氢气超声速膨胀凝结特性

氢气液化所需温度远低于天然气,需要设置更繁琐的深冷环节,液化流程复杂、占地面积大、投资成本高。超声速膨胀液化是一种新兴的气体液化分离技术,具有流程密闭、节能环保、成本低等优势。因此,提出将超声速膨胀液化技术引入氢气液化领域,并且为探究其可行性,基于流体力学计算软件FLUENT中的SIMPLE算法和k-ω湍流模型,采用Gyarmathy液滴生长模型,研究了氢气在不同入口压力(1.05 MPa、1.10 MPa、1.15 MPa)条件下的超声速流动与凝结特性。结果表明,氢气高速膨胀引起的低温效应将使氢气自发凝结,导致在短距离内快速形成液滴,证实了超声速氢气液化技术的可行性;氢气入口压力的提高,可有效增加氢气在Laval喷管入口的过冷度,从而使得气体凝结起始位置前移,增大液滴粒径,提高Laval喷管液化效率。

管道形状对超音速雾化降尘特性的影响

为治理煤矿行业中井下粉尘的污染问题,基于可压缩气流管内超音速流动理论,提出1种超音速雾化降尘技术;通过数值模拟的方法来研究不同结构、气动总压力对拉瓦尔喷管内超音速流动过程的影响,并通过激波、音速环以及轴向最大马赫数、轴线最大平均速度等现象来分析不同气动总压力下不同拉瓦尔喷管结构参数的超音速流动规律;搭建雾化特性实验平台,对最佳的喷管形状在不同的压力下进行降尘效率的计算,对比分析不同时刻和不同压力下降尘效率的变化规律。研究结果表明:凹形喷管在不同压力下的降尘稳定性最强,是制作雾化降尘喷头的最好选择。凹形喷管在不同压力下3种时刻的瞬时降尘效率都随着时间增加而逐渐升高,雾化降尘效果良好,当喷雾时间为3 min且气动压力为0.5 MPa时,凹形喷管的降尘效率为85.13%,降尘效率最高,降尘效果最好。研究结果可为治理煤矿井下采煤过程中的粉尘问题提供理论支持和治理手段。

基于拉法尔喷管的新型放空立管可行性研究

针对传统放空立管介质出口速度小、扩散高度低等缺点。文章基于理论分析和模拟的手段对新型放空立管进行可行性研究。结果表明,放空介质动能来源于进出口压差及介质焓值,放空过程是一个压降、温降过程;通过对新型放空立管合理设计,在不改变进出口条件下,可比传统立管出口速度提高37.5%~41.7%,提高可燃气体的扩散高度,降低对地面工作人员的潜在危害。该新型放空立管切实可行,可为今后放空立管的设计提供新的思路。

The gas jet behavior in submerged Laval nozzle flow

The behavior of the combustion gas jet in a Laval nozzle flow is studied by numerical simulations. The Laval nozzle is installed in an engine and the combustion gas comes out of the engine through the nozzle and then injects into the surrounding environment. First, the jet injection into the air is simulated and the results are verified by the theoretical solutions of the 1-D isentropic flow. Then the behavior of the gas jet in a submerged Laval nozzle flow is simulated for various water depths. The stability of the jet and the jet evolution with a series of expansion waves and compression waves are analyzed, as well as the mechanism of the jet in a deep water depth. Finally, the numerical results are compared with existing experimental data and it is shown that the characteristics of the water blockage and the average values of the engine thrust are in good agreement and the unfixed engine in the experiment is the cause of the differences of the frequency and the amplitude of the oscillation.

Laval喷管内甲烷-乙烷混合气体低温液化特性

为明确Laval喷管内甲烷-乙烷低温液化特性,获得天然气超声速液化过程中的流动与凝结参数,建立了甲烷-乙烷混合气体超声速凝结流动数学模型,开展了双可凝组分气体凝结相变实验验证,对比分析了凝结流动与等熵流动条件下的流场特性,并重点研究了甲烷-乙烷混合气体低温液化特性,结果表明:凝结相变发生之后,甲烷-乙烷混合气体流动过程中产生了微弱的凝结激波,相比于等熵膨胀过程,Laval喷管出口压力、温度升高,马赫数降低;凝结核数量在很短距离内从0急剧上升至最大值0.879×10^(21)m^(-3)·s^(-1)(约x=0.139m处);Laval喷管可获得的最大液滴半径4.476×10^(-7)kg^(-1),最大液滴数目4.462×10^(14)m^(-3),最大液相质量分数6.089%。

紧耦合气雾化拉瓦尔喷盘结构优化

采用计算流体动力学法模拟了紧耦合气雾化拉瓦尔喷盘气流喷射角(40°,50°,60°,70°,80°)、气流喷射宽度(15,20,25,30,35 mm)、导流管伸出长度(0.5,4.5,8.5 mm)对雾化室流场气流速度分布及其y轴上气流交汇点气流速度和导液管出口处静压的影响,得到了喷盘优化结构参数;采用优化结构喷盘制备18Ni300模具钢紧耦合气雾化粉末,测定了其性能。结果表明:随着气流喷射角增加,流场最大气流速度减小,气流交汇处气流速度和导液管出口处静压均增大;随着导流管伸出长度增加,流场最大气流速度先减小后增加,导液管出口处静压减小,气流交汇点气流速度未发生显著变化;随着气流喷射宽度增加,流场最大气流速度未产生显著变化,气流交汇点气流速度和导液管出口处静压均减小;根据模拟结果得到喷盘优化结构参数为气流喷射角60°、气流喷射宽度30 mm、导流管伸出长度4.5 mm,此条件下制得的18Ni300模具钢紧耦合气雾化粉末形状规则,尺寸小且均匀,细粉收得率最大,粉末流速和松装密度较大,综合性能最佳。

基于Laval喷管的滑动电弧放电等离子体发生器及其工作特性分析

为了研究产生于Laval喷管中的一种新型滑动电弧放电的物理特性,研究了不同流量工作气体(空气)条件下产生的等离子体电弧的伏安特性,并利用高速摄影仪对此种新型等离子体的滑动电弧发展过程进行了跟踪,记录了滑动电弧等离子体击穿—延长—电弧最大—熄灭的循环过程。结果表明:随着工作气体流量的增加,电极电压波形出现突变的频率越来越高;电流波形随着气体流量的增加除了击穿时突变点增多外大致形状不变,近似于正弦波形,且最大值都为0.4A;半周期内的平均电压在629～1 347V范围内变化。分析得出,流量变化对这种滑动电弧放电的伏安特性,特别是电压特性存在剧烈影响,这一点也可以从高速摄影所得图像中看出。

基于Laval喷管的圆管爆轰驱动近似解

本文将圆管在滑移爆轰驱动下的运动与Laval喷管扩张段进行对比,利用Laval喷管的一维理论,推导出了圆管在炸药爆轰驱动下的二维抛掷公式。对于气体多方指数γ≠3的情况,采用小参数摄动法进行了求解。计算结果表明,在小抛掷角范围内,该方法有很好的计算精度。

超音速两相膨胀分离及制冷液化的研究进展

超音速膨胀降温并结合旋流分离技术是一种新型气体液化分离技术,近年来主要应用于分离多组分气体中的高凝点组分。介绍了超音速旋流分离器的2种典型结构;归纳了Laval喷管中凝结相变的理论发展、数值模拟、实验研究和分子模拟4个方面内容;对超音速旋流分离器中的激波问题、结构优化进行了分析总结;大量实验及现场应用证明了超音速旋流分离器具有节能环保、无运动部件、无需添加化学药剂等优势,在天然气净化处理等领域已得到广泛应用。下一步研究可从单组分、多组分气体凝结相变机理、提升液化效率等方面入手,促进超音速旋流分离技术在普冷温区、氢氦低温温区的液化及制冷技术应用。

氧枪喷头Laval喷管内流场的数值模拟

根据实际生产的氧枪喷头按比例建立了Laval喷管模型。应用商业软件Fluent6.2,采用κ-ε模型,耦合隐式求解器,讨论了喷管内不同数学模型的适应性,得出RNGκ-ε模型模拟喷管内激波较为理想。分析了Laval喷管内不同工况下(P_0=0.11～1.0 MPa)的流场、马赫数及压力的分布情况,得出喷管入口处滞止压力影响Laval喷管内部流动状况,但不影响出口流动工况,出口工况主要取决于喷管的几何结构。

Laval型雾化器气液流动特性研究

喷嘴出口气流速度和气液质量流率比是影响液态金属雾化效果的两个主要因素。为改善雾化效果,对现有环缝型雾化器进行改进,出口采用Laval型。建立了喷嘴出口速度、气体与金属质量流率的表达式,获得稳定气、液质量流率比的坩埚背压与金属液面高度的关系。通过实验方法建立了采用限制型Laval喷嘴导流管出口负压值与雾化压力之间的关系。

Supersonic expansion and condensation characteristics of hydrogen gas under different temperature conditions

This paper introduced supersonic expansion liquefaction technology into the field of hydrogen liquefaction.The mathematical model for supersonic condensation of hydrogen gas in a Laval nozzle model was established.The supersonic expansion and condensation characteristics of hydrogen gas under different temperature conditions were investigated.The simulation results show that the droplet number rises rapidly from 0 at the nozzle throat as the inlet temperature increases,and the maximum droplet number generated is 1.339×10^(18)kg^(-1)at inlet temperature of 36.0 K.When hydrogen nucleation occurs,the droplet radius increases significantly and shows a positive correlation with the increase in the inlet temperature,and the maximum droplet radii are 6.667×10^(-8)m,1.043×10^(-7)m,and 1.099×10^(-7)m when the inlet temperature is 36.0 K,36.5 K,and 37.0 K,respectively.The maximum nucleation rate decreases with increasing inlet temperature,and the nucleation region of the Laval nozzle becomes wider.The liquefaction efficiency can be effectively improved by lowering the inlet temperature.This is because a lower inlet temperature provides more subcooling,which allows the hydrogen to reach the thermodynamic conditions required for large-scale condensation more quickly.

收缩管与拉瓦尔管在液体雾化中的对比研究

为探究新型透皮给药方式中不同形状微管对雾化的影响,本文以收缩管和拉瓦尔管为对象展开研究.首先,我们使用相位多普勒粒子分析仪(Phase Doppler Particle Analyzer, PDPA)对经两类微管雾化后的液滴进行速度和粒径分布的测量.然后,为了解管内流动情况,我们利用动态压强传感器对管内气体压强进行了测量,并利用纹影法对管内流动情况进行观察.最后,我们利用高速液滴对皮肤模型进行了喷射试验,其中使用亚甲基蓝和伊文思蓝作为染色试剂,新鲜猪耳作为喷射对象.PDPA实验表明,液滴经拉瓦尔管的雾化比经收缩管的雾化更充分.压强测量结果表明拉瓦尔管内存在激波,进而证明了管内发生过超声速.纹影实验更直观地表明在本研究关注的拉瓦尔管内,气体流动在扩张段形成的不是正激波,而是两道交错的斜激波.皮肤模型喷射实验结果表明雾化后高速液滴穿透了角质层,展示了微喷管在医美行业透皮给药中有潜在的应用价值.该工作为新颖透皮给药方式的进一步研究奠定了基础.