Prediction of atomization characteristics of pressure swirl nozzle with different structures

The structure of the pressure swirl nozzle is an important factor affecting its spray performance.This work aims to study pressure swirl nozzles with different structures by experiment and simulation.In the experiment,10 nozzles with different structures are designed to comprehensively cover various geometric factors.In terms of simulation,steady-state simulation with less computational complexity is used to study the flow inside the nozzle.The results show that the diameter of the inlet and outlet,the direction of the inlet,the diameter of the swirl chamber,and the height of the swirl chamber all affect the atomization performance,and the diameter of the inlet and outlet has a greater impact.It is found that under the same flow rate and pressure,the geometric differences do have a significant impact on the atomization characteristics,such as spray angle and SMD(Sauter mean diameter).Specific nozzle structures can be customized according to the actual needs.Data analysis shows that the spray angle is related to the swirl number,and the SMD is related to turbulent kinetic energy.Through data fitting,the equations for predicting the spray angle and the SMD are obtained.The error range of the fitting equation for the prediction of spray angle and SMD is within 15% and 10% respectively.The prediction is expected to be used in engineering to estimate the spray performance at the beginning of a real project.

Supersonic swirling characteristics of natural gas in convergent-divergent nozzles

The supersonic nozzle is a new apparatus which can be used to condense and separate water and heavy hydrocarbons from natural gas.The swirling separation of natural gas in the convergent-divergent nozzle was numerically simulated based on a new design which incorporates a central body. Axial distribution of the main parameters of gas flow was investigated,while the basic parameters of gas flow were obtained as functions of radius at the nozzle exit.The effect of the nozzle geometry on the swirling separation was analyzed.The numerical results show that water and heavy hydrocarbons can be condensed and separated from natural gas under the combined effect of the low temperature（-80℃） and the centrifugal field（482,400g,g is the acceleration of gravity）.The gas dynamic parameters are uniformly distributed correspondingly in the radial central region of the channel,for example the distribution range of the static temperature and the centrifugal acceleration are from -80 to -55℃and 220,000g to 500,000g,respectively,which would create good conditions for the cyclone separation of the liquids.However,high gradients of gas dynamic parameters near the channel walls may impair the process of separation.The geometry of the nozzle has a great influence on the separation performance. Increasing the nozzle convergent angle can improve the separation efficiency.The swirling natural gas can be well separated when the divergent angle takes values from 4°to 12°in the convergent-divergent nozzle.

A swirling jet from a nozzle with tangential inlets and its characteristics in breaking-up rocks

In order to apply a swirling jet to a PDC drill bit, the nozzle performance influenced by nozzle inlet geometric parameters and rock breaking tests under submerged conditions were studied. Numerical simulation was used to study the influence of the nozzle structure on the swirling intensity and nozzle discharge coefficient. Simulation results indicate that spreading angle of the swirling jet is greater than that of＂ the non-swirling jet, and the swirling intensity of the jet is strongly influenced by the length of the nozzle body but weakly by the number of tangential inlets. Rock breaking tests were conducted to evaluate the performance of the swirling jet. It is found that the swirling jet shows a lower threshold pressure to break the rock samples and could break rock more efficiently compared with the non-swirling jet.

Turbulent flow in converging nozzles,part one:boundary layer solution

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer as- sumptions and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order Adams predictor-corrector method. The free vortex and uniform velocity profiles are applied for the tangential and axial velocities at the inlet region, respectively. Due to the lack of experimental data for swirling flows in converging nozzles, the developed model is validated against the numerical simulations. The results of numerical simulations demonstrate the capability of the analytical model in predicting boundary layer parameters such as the boundary layer growth, the shear rate, the boundary layer thickness, and the swirl intensity decay rate for different cone angles. The proposed method introduces a simple and robust procedure to investigate the boundary layer parameters inside the converging geometries.

Flow field, heat transfer and inclusion behavior in a round bloom mold under effect of a swirling flow submerged entry nozzle

Flow field,heat transfer and inclusion behavior in a 700 mm round bloom mold under the effect of a swirling flow submerged entry nozzle(SEN)were investigated with the aim to enhance the casting process.The results indicate that the impinging flow phenomenon,which is commonly observed in conventional single-port SEN casting,was completely suppressed by the swirling flow SEN coming from a novel swirling flow generator design in tundish.Steel from the SEN port moved towards the mold wall in 360 direction,leading to a uniform temperature distribution in the mold.Compared to a conventional single-port SEN casting,the steel super-heat was decreased by about 5 K at the mold center,and the temperature was increased by around 3.5 K near the meniscus.In addition,the removal ratio of inclusions to the mold top surface in the swirling flow SEN casting was found to be increased.Specifically,the removal ratio of spherical inclusions with diameters of 1,10,50 and 100μm was increased by 18.2%,18.5%,22.6% and 42.7%,respectively.Furthermore,the ratio was raised by 18.2%,20.8%,21.5% and 44.1%for non-spherical inclusions,respectively.

筒形五喷嘴燃烧室冷态时均流场特性实验研究

为深入研究五喷嘴燃烧室的流场特性,采用高频PIV测量方法对燃烧室中心截面的冷态流场开展实验研究,主要分析了燃烧室入口速度以及中心喷嘴旋流强度对五喷嘴燃烧室中心截面的时均流场特征的影响。实验结果表明:中心喷嘴和外侧喷嘴出口均存在主回流区,外侧喷嘴与燃烧室壁面间存在角回流区,相邻喷嘴射流相互干涉。喷嘴旋流强度相同时,入口速度由10 m/s增大到20 m/s,中心喷嘴和外侧喷嘴的回流区形态、主回流区长度、最大回流速度位置和气流合并点位置基本不变。入口速度为14.3 m/s时,中心喷嘴旋流强度由0.63增大到0.84,中心喷嘴回流区长度增大,外侧喷嘴回流区长度不变,主回流区最大回流速度显著增大,且更靠近喷嘴出口,气流合并点径向位置基本不变,轴向位置向喷嘴出口移动。

SCR系统压力旋流式喷嘴结构对近场喷雾特性的影响

选择性催化还原(SCR)系统是柴油机脱除尾气NO_(x)的核心,喷嘴的雾化性能直接影响NO_(x)转化率及尿素结晶,压力旋流式喷嘴比直流式喷嘴更有性能优势.以新设计的一款压力旋流式喷嘴为对象,结合试验数据,基于流体体积函数(VOF)法,耦合喷嘴内旋流与喷嘴外近场喷雾开展三维数值模拟,精准获取旋流液膜厚度、液膜锥角.基于喷孔内部流场与索特平均直径(SMD)的关系模型,实现喷嘴结构对喷雾雾化性能的直接耦合研究,进而获得了旋流室长度、旋流室直径、出口段长度和出口段孔径等压力旋流式喷嘴关键结构参数对喷雾性能的影响特性,结果表明:喷嘴几何参数调整需由气核生长情况判断;当气/液两相分界面呈多级阶梯型时,减小旋流室长径比、出口段长径比均可有效降低喷雾粒径,增强雾化效果.该新设计的压力旋流式喷嘴具备SMD小于30μm的潜力.

某电厂旋流燃烧器烧损原因分析及解决措施

本文主要介绍了某电厂旋流燃烧器喷口烧损事故的情况并针对旋流燃烧器出现的喷口烧损变形情况进行了原因分析,同时提出了解决措施,为同类型机组后续设计和运行提供了一定的借鉴经验。

自激扫掠喷嘴气液两相流场特性研究

为研究自激扫掠喷嘴内、外流场结构,分析高频扫掠液柱的变形和破碎过程,首先采用高速阴影成像法,在0.1~4.0 MPa压降范围内,对喷嘴的扫掠频率及扫掠张角等基本工作特性进行了测量;其次,采用实验测量结果对气液两相数值模型进行了校核;最后,采用校核后的数值模型对喷嘴内、外气液两相流场结构开展了模拟研究。研究结果表明:喷嘴内部为单相流动,无气相介质的回流;液柱的高频扫掠使其在喷嘴出口形成了一个扇形液面;液柱的自旋增强了气相对液柱的剪切作用;在扇形液面两侧,液柱的反向偏转会导致其变形和破碎;在扇形液面中间,液柱的横向扫掠形成一个高速气相区,气相速度可达液相的3倍,提高了韦伯数,使得“液丝状”的液柱进一步破碎并扩散。

长旋流腔敞口型离心喷嘴注气雾化特性试验

以水和煤油模拟液作为液体工质,氮气和氦气作为注入气体,采用可视化试验技术和激光多普勒测速仪试验研究了不同气体流量作用下的长旋流腔敞口型离心喷嘴的雾化特性,包括喷注液膜破碎形态、气液两相混合建压与雾化粒径。研究结果表明:随着气液质量流量比升高,破碎模式逐步由轮缘型破碎、多孔型破碎过渡到爆裂型破碎。雾化过程中在喷嘴出口处伴随间歇性的中心气流冲击,冲击长度随气体流量升高而增大,但冲击频率随气体流量呈非线性变化,在气体流量较高或较低时的冲击频率反而升高。注气显著提高了喷注压降和雾化均匀性,相同气体流量的条件下,氦气相较于氮气具有更快的建压速度和更高的建压值,但氦气作用下的两相混合建压时混合室内的压力波动更为剧烈;氦气吹除的雾化粒径普遍小于氮气,但过高的氦气注气流量易引起气流冲击,引起冲击间隔时间内的雾化分布不均。

Experimental investigation on the spray characteristics of agricultural full-cone pressure swirl nozzle

The spray characteristics of a full-cone pressure swirl nozzle have been investigated in this study.The results were defined by Reynolds number,which focuses on the breakup of liquid film,droplet size,velocity,and liquid volume flux under different Reynolds numbers at the near-field spray.The spray structure was visualized using a high-speed camera,and the characteristics of droplets were measured using a Phase Doppler Anemometer(PDA)in both the radial and axial directions.The tests were carried out at varying spray pressures(0.2 to 1.0 MPa),corresponding to different Reynolds numbers(5369 to 12006).It was found that when the Reynolds number rises,the liquid became more unstable after leaving the nozzle,causing the liquid film to break up faster.According to the measurements of PDA,the coalescence of droplets increased due to the centrifugal effect.What’s more,the velocity of the droplets fluctuates significantly in the radial direction,and the droplets with a smaller particle size had a higher average velocity.From the perspective of liquid distribution,the increase in Reynolds number caused the spray liquid to move in the radial direction gradually.In contrast,the liquid volume distribution changed in the radial direction more obviously than in the axial direction,growing to the maximum along the radial direction and gradually reducing.It can provide a reference for selecting operating parameters for actual agricultural spray operations and the design of electrostatic nozzles through the research on breakup and droplet characteristics.

Structural Optimization of Electromagnetic Swirling Flow in Nozzle of Slab Continuous Casting

During the slab continuous casting process, the flow field of molten steel in the mold plays a decisive role in the quality ofthe slab. In this paper, electromagnetic swirling flow in nozzle technology is proposed to control the flow field in mold.This technology can drive molten steel to rotate inside the submerged entry nozzle by electromagnetic force, therebycontrolling the flow field. This research shows that it can reduce the impact of molten steel on the bottom of nozzle andpartly reduce the negative pressure at the upper part of nozzle outlet which is even eliminated by optimizing the structureand angle of nozzle. The area of heat flux of the mold wall becomes larger, and the crest value of heat flux gets lower thanthat without swirling in nozzle and any nozzle optimization. The meniscus fluctuates smoothly, and the flow velocity at thetop surface is within a reasonable range. The temperature field distribution in the mold is uniform which was beneficial tothe growth of equiaxed crystal and decreased element segregation.

Effect of Nozzle Inlet Shape on Annular Swirling Flow with Non-Equilibrium Condensation

Recently,by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow,a separating and extracting techniques of condensate gas have been developed.This technique can reduce the size of the device and don't use chemicals.In the present study,by using a non-equilibrium condensation phenomenon of moist air occurred in the supersonic flow in the annular nozzle composed of an inher body and an outer nozzle with a swirl,the possibility of separation of the condensable gas and the effect of shape of nozzle inlet on the flow field were examined numerically.

离心式喷嘴结构参数的多目标优化设计

为提高某型号航空燃油离心式喷嘴的综合雾化性能,对喷嘴的结构参数进行优化设计。基于流体体积(VOF)模型,模拟了喷嘴的内外流场,并通过试验验证了仿真模型的可靠性。为节省多次试验和数值模拟的成本,基于响应面法(RSM)建立了以喷嘴扩张段长度、等直段直径、等直段长度、收缩半角、扩张半角为设计变量,雾化锥角和质量流率为响应变量的代理计算模型。基于得到的表达式,分析了设计变量对响应变量的贡献度和交互影响作用,结果表明:扩张半角对雾化锥角的贡献最大,呈正相关;质量流率受等直段直径的影响最为显著,随着等直段直径的增加而增加,但随着收缩半角的增大而减小。以雾化锥角和质量流率为优化目标,采用NSGA-Ⅱ算法进行多目标优化,优化结果表明:优化后的结构参数使得离心式喷嘴的雾化锥角和质量流率分别提高了8.3%和32.4%。

室外造雪机用旋流喷嘴雾化性能实验研究

喷嘴作为室外造雪机成雪过程重要的雾化部件,是决定成雪速率和成雪量的关键。本文针对国产室外造雪机用旋流结构喷嘴,搭建了通用的雾化性能测试装置,研究了供水压力对喷嘴雾化效果和液滴与环境换热表现的影响。结果表明:旋流结构喷嘴雾化过程的低压段,流体呈空心纺锤状,其锥角随压力变化显著,雾化效果较差;而高压段流体呈空心锥状,锥角相对稳定;雾化稳定后,喷嘴的流量随压力进一步提高,索特平均粒径(Sauter mean diameter,SMD)则逐渐降低,雾化锥角稳定在约76°;同时压力升高可缩短喷雾换热至环境温度的时间,表现为更高的热传递效率。研究结果可为高性能雾化部件结构设计提供理论支撑。

入口雷诺数对压力旋流喷嘴雾化特性的影响

为了揭示介质流量和介质黏度在压力喷嘴雾化过程中的作用机制,采用大涡模拟(LES)与体积函数模型(VOF)相结合的模拟方法,探究了喷嘴内部流动情况,分析了入口雷诺数对喷嘴流量系数、雾化角和雾化粒径等雾化特性的影响。结果表明:随着雷诺数的增加,喷嘴出口液膜厚度变薄,喷嘴流量系数降低;在高雷诺数下,流量系数受其影响较小;随着雷诺数增加,喷嘴雾化角增大,当雷诺数低于1000时,雾化角增大现象更为明显,相同雷诺数下雾化角几乎相等;当雷诺数较高时,雾化液滴索特平均粒径更均匀,液滴粒径分布更接近R-R分布特征。

喷嘴特性对双旋流燃烧室出口温度分布影响的实验研究

本文以双旋流全环燃烧室为试验对象,在高温高压试验条件下,通过调整全环燃油喷嘴的流量离散度和径向位置来研究其对出口温度分布的影响。试验结果表明,当喷嘴燃油流量离散度控制在±4%以内时,采用简单的大、小流量喷嘴间隔搭配的方案即可保证出口温度分布的均匀性;当燃油流量离散度放大到4%~8%时,采用本实验研究的搭配方案仍可保证出口温度分布的均匀性;当燃油流量离散度放大到10%时,通过调整喷嘴搭配方案已经无法保证出口温度分布均匀性。燃油喷嘴径向位置较火焰筒头部中心线偏离旋流杯腔道高度的11.5%以内时,不影响出口温度分布的均匀性。

压力旋流雾化喷嘴雾化特性的研究

针对喷雾降尘中运用最为广泛的压力旋流雾化喷嘴,采用Fluent软件进行数值模拟分析,研究不同条件下压力旋流雾化喷嘴流场特性的变化。结果表明:空气芯始终存在于压力旋流雾化喷嘴内部;喷嘴出口处的轴向速度在速度场中起决定性作用,且在工作压力为4~6 MPa时,速度增量开始趋缓;喷嘴的雾化锥角随压力变化不大,当喷嘴出口直径在1~2 mm之间时,雾化锥角随喷嘴直径的增大而增大,且当喷嘴出口直径为2 mm时雾化锥角达最大值;结合工程实际,宜选择直径为2 mm的压力旋流雾化喷嘴在4~6 MPa的工作压力下工作。

Effects of Variable Jet Nozzle Angles on Cross-Flow Suppression and Heat Transfer Enhancement of Swirl Chamber

This paper investigated the effects of variable jetting nozzle angles on the cross-flow suppression and heat transfer enhancement of swirl cooling in gas turbine leading edge. The swirl chamber with vertical jet nozzles was set as the baseline, and its flow fields and heat transfer characteristics were analyzed by 3D steady state Reynolds-averaged numerical methods to reveal the mechanism of cross-flow weakening the downstream jets and heat transfer. On this basis, the flow structure on different cross sections and heat transfer characteristics of swirl chamber with variable jetting nozzle angels were compared with the baseline swirl chamber. The results indicated that for the baseline swirl chamber the circumferential velocity gradually decreased and the axial velocity gradually increased, and the cross-flow gradually formed. The cross-flow deflected the downstream jets and drawn them to the center of the chamber, thus weakening the heat transfer. For swirl chamber with variable jetting nozzle angles, the air axial velocity is axial upstream, opposite to the mainstream, so that the impact effects of cross-flow on the jets were reduced, and the heat transfer was enhanced. Furthermore, with the increase of axial velocity along the swirl chamber, the jetting nozzle angle also gradually increased, as well as the effect of cross-flow suppression, which formed a relative balance. For all swirl chambers with variable jet nozzle angles, the thermal performance factors were all larger than 1, which indicated the heat transfer was enhanced with less friction increment.

基于数值方法的燃气轮机贫预混旋流燃烧室单头部结构设计

为分析贫预混旋流燃烧室头部结构特性影响,采用计算流体力学方法研究了中心体端面形状、空气流量,燃料喷孔数量、位置,以及头部扩张比对燃烧火焰、流场及火焰动态响应的影响。结果表明:空气流速增大到一定值后,火焰形态基本保持不变;增加压力面燃料孔数量,高放热率区集中在中心回流区根部,同时增加压力面和吸力面燃料孔数量使得中心回流区根部温度更低,有降低热力NOx的趋势;增加火焰筒直径,有助于中心回流区沿径向扩张,导致火焰更长、更细;将中心体端面改成椭圆,会缩短火焰轴向长度;改变中心体端面形状基本不影响火焰传递函数幅值和相位,但增加燃料孔数量明显改变火焰传递函数相位。