柴油机喷油嘴内壁面粗糙度对空化效应的影响

基于k-ε湍流模型及混合均相流(Homogeneous Equilibrium Mixture,HEM)模型,研究了不同喷射压力(30MPa、180MPa)条件下喷油嘴喷孔内壁面粗糙度对空化流动特性的影响。结果得出:随着喷孔内壁面粗糙度的增大,喷孔内部空穴强度减弱,喷孔内部的湍动能增强;提高喷孔内壁面的粗糙度对喷孔出口的质量流量影响不明显,但是在高喷射压力条件下喷孔出口质量流量略有增加;在高喷射压力条件下随着喷孔内壁面粗糙度的增大喷孔出口的平均速度显著减小,喷孔出口处的湍动能显著增大,而在小喷射压力条件下随着粗糙度的增大,喷孔出口的平均速度降幅较小,喷孔出口处的湍动能增幅较小;喷孔出口处X轴线上在喷孔上壁面空穴区域的湍动能较喷孔底部与中部区域大,空穴的产生、溃灭有利于增强喷孔出口处的湍流强度。     

不同启喷压力下喷油嘴内部两相流动仿真研究

本文建立了喷油嘴内部燃油两相流动CFD模型,并对多孔喷油嘴在不同启喷压力下进行喷孔内部空穴两相湍流稳态和瞬态流动的三维数值模拟。得出喷油嘴内部空穴基本发生在喷油嘴与喷孔结合部处,并沿喷孔方向延伸;喷油嘴进口压力的提高导致喷孔内空穴区域变大,喷孔流量增大。不同启喷压力下喷油嘴瞬态流动结果,为提高柴油机气缸内喷雾发展和燃烧仿真模拟的准确性,提供了必需的喷油嘴边界条件。模拟计算结果与已有的实验结果吻合较好。     

基于CFD的喷嘴结构参数对各孔内部流动特性影响研究

采用经试验验证的三维气液两相流空穴模型,以各孔非均布的多孔柴油机喷油器为依托,详细研究喷孔结构参数对各孔内部流动特性的影响及其影响规律。结果表明:随着喷孔入口导圆半径的增加,各孔内的空化效应逐渐减弱,但各孔出口平均流速、质量流量和流量系数均逐渐提高;喷孔长度的增加对各孔内的空化效应具有一定的抑制作用,同时,各孔出口的平均流速、质量流量和流量系数逐渐降低;随着喷孔直径的增加,各孔内的空化效应逐渐增强,质量流量逐渐提高,但流量系数的变化并不是很明显。     

不同燃油温度下柴油机喷嘴空穴流动特性试验研究

作为喷射系统的终端,喷油器内部的空穴流动对燃油雾化具有重要影响。采用比例放大透明喷嘴,研究不同燃油温度对喷嘴内空穴流动及其对近场喷雾的影响。引入无单位参数空穴数表征喷油器内燃油空化程度,研究发现燃油温度升高,其空穴初生时的压力减小,同一空穴数下,空穴程度更强烈。同时,试验观察到喷嘴内空穴区域的不对称性,喷孔管壁下壁面的空穴分布远大于上壁面的空穴分布;发生超空穴之后,随着空穴数的增加,试验结果中喷嘴内部的空穴流动变化不太明显,但仿真结果中看出喷孔出口流速减小。相同燃油温度下,随着空穴数增加,体积流量增加,流量系数减小,空穴相对面积增加,近场喷雾锥角增大;相同空穴数下,燃油温度增加使体积流量和流量系数都增加,空穴相对面积逐渐增大,近场雾化效果更好。     

柴油机喷嘴结构对喷雾特性影响的耦合模拟研究

高压共轨系统能有效地改善柴油机的喷雾质量,但随着燃油喷射压力的增加,燃油雾化过程变得更加复杂。而喷嘴内部湍流和空穴现象对喷雾雾化有重要的影响,特别是空穴现象。利用同步辐射X射线同轴相衬成像技术准确获得喷嘴几何结构尺寸,建立精确的喷嘴内部流动模型,建立起耦合喷嘴内空穴流动的耦合喷雾模型,分析喷嘴内空穴流动对燃油喷射雾化的影响。利用在高压共轨喷雾试验台架上的高压喷雾试验,验证该喷雾模型的准确性。利用该验证后的喷雾模型直接得到喷嘴结构参数,包括喷孔长径比、喷孔入口圆角半径及喷嘴压力室结构对喷雾特性的影响,得出喷孔入口圆角半径和压力室结构对喷雾的索特平均直径有较大的影响。研究结果为柴油机燃油喷射系统的优化提供了理论依据。     

基于OpenFOAM的喷孔内部流动与近场雾化的数值模拟

基于OpenFOAM平台,对Schnerr-Sauer空化模型的蒸发和凝结源项进行了修正,建立了一种考虑热力学效应的空化模型,并分别采用原始模型和修正空化模型对燃油在喷孔内部的流动及喷嘴近场的雾化过程进行了模拟计算。修正空化模型与原始模型相比,喷孔内部的空化强度加强,空穴范围扩大,喷孔近场区域的未扰液核变短,燃油分裂雾化更加细小,说明修正空化模型促进燃油的初次分裂及雾化。     

基于CFD的柴油机多孔喷油器各孔内部流动特性差异研究

采用混合多相流空穴模型,进行喷孔轴线与针阀轴线夹角各异的多孔喷油器喷嘴内三维气液两相流数值模拟,详细研究多孔喷油器各孔内部流动特性的差异及喷油压力和喷油背压对其影响规律。结果表明:对于喷孔轴线与针阀轴线夹角各异的多孔喷油器,相同喷射条件下,随着喷孔轴线与针阀轴线夹角的增大,喷孔内的空化效应逐渐增强,质量流量和流量系数逐渐降低;随着喷油压力的提高,各孔内的空化效应均逐渐增强,质量流量均逐渐升高,流量系数均逐渐降低;随着喷油背压的提高,各孔内的空化效应逐渐减弱,质量流量逐渐降低,但流量系数却逐渐提高。     

基于K系数喷嘴喷孔内空化现象的数值模拟

建立了某喷油器流场的二维模型,利用混合多相流模型加空穴模型对整个几何模型区域的流场进行了数值模拟计算.基于这一模型定义了K系数,并分析了不同K系数对喷孔内空穴分布的影响.总结出了喷孔的扩张系数K对喷孔中空化流的影响变化规律并且得到了不同K系数对出口处质量流量和喷孔内气体总体积的影响.数值计算结果表明,在一定的K值范围内,K＜0喷孔随着扩张程度的增大,空化现象加剧,而K＞0喷孔则抑制空化现象的产生.     

喷嘴结构参数对流体特性影响的三维流场模拟

为了改善柴油机D6114喷油嘴291 DLLA150 FC PV01内部燃油流动状况,使喷入气缸内的燃油达到较好的雾化质量,在原有喷嘴基础上,针对喷嘴结构参数长径比、喷嘴入口过渡圆角及喷孔锥角设计了9种方案。在CFD(计算流体动力学)软件中建立了喷嘴内部流场的三维模型,对整个流场区域进行了流体动力学模拟计算。分析了喷嘴结构参数对喷孔内部空化程度、湍动能及流速的影响,得出:随着长径比(L/D)的减小,燃油在喷孔中的空化程度增强,湍动能减小,流速增加;随着过渡圆角与直径比(r/D)的增大,喷孔内部流体空化程度增强,流速增大,湍动能减弱;随着喷孔锥角(θ)的增大,喷孔内燃油空化程度加强,湍动能减弱。     

基于两相流空穴模型的比例阀流量特性分析

比例阀是大型柴油机柱塞泵核心元件,比例阀的性能关系到液压控制系统的特性.针对比例阀节流口对流量特性影响等问题,采用数值模拟和实验相结合的方法,分析了比例阀不同阀口结构下的流动特性.首先,基于Fluent仿真软件两相流Schnerr-Sau-er空穴模型,分析了3种不同节流口下阀的空穴情况和流量特性;然后,在比例阀性能实...     

空化喷嘴出口形状的研究

对收缩-扩散型出口空化喷嘴的出口段泡液流稳态解的分析表明：泡液流中很小的空隙率亦强烈地影响着其流动特性。试验证明具有收缩-扩散形出口流道的空化喷嘴的空化效果更好。     

基于Fluent的超薄连续铸轧三维流场仿真分析

基于计算流体软件Fluent,比较全面地分析双辊超薄连续铸轧的流场,特别是铸嘴型腔三维流动现象及其特点.分析铸轧区对流场的作用.铸轧区有利于铸嘴出口速度的均匀流动,有利于速度均匀混合,但不能彻底消除速度梯度.把计算的铸嘴出口处的流体速度与实验结果相比较,两者基本吻合,并得出结论:分流块的形状与位置是影响铸轧流场的主要原因之一,常规铸轧常用铸嘴熔体出口速度相对误差达38%,不能满足超薄连续铸轧技术的需要.     

收缩-扩散型喷嘴内高速泡液流稳态解的分岔

空化水射流技术的关键是空化喷嘴 ,实验证明空化喷嘴出口形状对喷嘴的空化效果影响很大。对在具有收缩 扩散形状的喷嘴内高速泡液流稳态解的分析表明 :泡液流中很小的空隙率亦强烈地影响着其流动特性。当空隙率为临界值αc=1.895 993× 10 -4时 ,泡液流稳态解出现分岔现象。收缩 扩散型出口形状更利于喷嘴产生空化     

Optimal design of supersonic nozzle contour for altitude test facility

This paper develops a robust and practical design for supersonic nozzles to be used in an altitude engine test facility. Although many studies have been conducted on nozzle design, none of these present a robust yet practical and simple method for designing supersonic nozzles. This research attempts to develop such design for supersonic nozzles by combining method of characteristics (MOC), optimization algorithm, and computational fluid dynamics analysis for design verification. Preliminary design optimal techniques were adopted to reduce nozzle length while keeping the exit area constant in the design. Optimization produced a smooth flow by generating a parallel and uniform flow at the exit. A two-dimensional model was initially used because of the axisymmetrical characteristic of the flow in this study. The optimal nozzle was designed for the operation of a test facility at Mach number 2.3 and altitude of 7 km. The optimal design produced a uniform and parallel flow at the given test condition.     

脉冲空化多孔射流钻头的结构设计研究

在多孔射流钻头的基础上,设计了脉冲空化多孔射流钻头,分析了其工作原理:当流体冲击叶轮高速旋转时,可对侧向孔眼入口处的流场产生有规律性的扰动,形成脉冲射流;同时,高速旋转的叶轮可以降低叶轮附近流体的局部压力,可产生许多微小空泡,夹杂在射流中形成空化射流。同时形成的2种射流进而耦合成脉冲空化射流。并利用流体力学和机械设计理论对射流钻头本体、叶轮轴和叶轮的结构参数进行了研究,研究结果可为脉冲空化多孔射流钻头结构设计提供依据。     

Effects of the geometric orientations of the nozzle exit on the breakup of free liquid jet

Free liquid jets are produced through various geometric orientations of the nozzle exit. The breakup lengths of liquid jets under various geometric orientations of the nozzle exit were studied. Images of jets were captured using a high-speed camera with a maximum frame rate of 1000 frames per second and were analyzed to determine the dynamics between jets and breakup lengths. The breakup length of jets changes with the cut angle of the nozzle exit. In addition, adding polymer reduces the effect of the cut angle of the nozzle exit on the breakup length for an entire range of velocities. The effect of the cut angle on breakup length is predominant for aqueous solutions with surfactants. This work provides motivation for further computational research to study jet dynamics in a partially covered nozzle exit, such as the case in which the boundary conditions near the nozzle opening is more complex with the cut angle and its vertex position, which directly reflects liquid jet dynamics.     

Performance curve available for non-steady flow through Venturi-like reverse flow diverter

A reverse flow diverter (RFD) consists of a driving nozzle, a diffuser, and a suction gap that separates the nozzle and diffuser. Thus, the RFD is a Venturi-like fluidic component with three ports. The jet flow emanating from the driving nozzle exit can entrain the ambient fluid and transport it to a high elevation. During this time, the flow through the RFD is non-steady, which makes it difficult to measure the flow depending on the pressure drop. In this study, a series of tests was carried out to evaluate this fluid flow with different contraction ratios, suction gap lengths, fluid properties, inlet flow rates, and inlet pressures. A performance curve was formulated that can be expressed as an exponential equation correlating the non-dimensional Euler number, pressure ratio, and suction factor. The performance curve is not affected by the driving nozzle exit diameter and suction length of the RFD. The performance curve makes it possible to measure the flow out of a RFD depending on the pressure drop.     

收缩喷嘴内部流道型线对射流流场的影响

为研究收缩喷嘴内部流道形成对射流流场的气体动特性参数的影响，根据可压缩流体轴对称N-S方程，采用非结构网格和二阶精度的有限体积法，对不同内部流道形线的喷嘴自由射流进行数值模拟。亚声速射流采用RNGk-ε湍流模型，超声速射流采用S-A湍流模型，计算结果与实验较吻合。在亚声速流动中，收缩喷嘴的收缩角大小会影响其对射流的阻滞效果，内部流道形线设计为维多辛斯基曲线可以获得更好的流场动特性参数，有利于提高喷嘴的工作效率。在超声速流动中，喷嘴流道型线对出口膨胀波的角度与强弱影响较大，要根据射流的有效作用区域选择合适的喷嘴，才能使能量的损失最小。若要获得较佳的外部流场参数，优化喷嘴内部流道设计十分重要。     

A study on the air knife flow with Coanda effect

The coating thickness in hot-dip zinc galvanizing process is of practical importance in determining the quality of product, and its control is often done using the gas wiping through an air knife system. Such a gas wiping method causes a technical problem of splashing from the strip edge to have a harmful effect on the performance of the galvanizing process and the product quality. The present study aims at investigating the effectiveness of Coanda nozzle to reduce the strip splashing problem. A blow-down wind tunnel has been used to experimentally investigate the detailed flow field near the exit of Coanda nozzle and on the strip edge. A computational work has been performed with the help of a computational fluid dynamics method. The three-dimensional, compressible Navier-Stokes equations have been solved using a fully implicit finite volume scheme. The results obtained show that Coanda nozzle effectively reduces the splashing problem, leading to improvement of the whole galvanizing process.     

二维超音速喷管型线设计仿真研究

采用计算软件FLUENT,对四种经典收缩段型线下的流场特性进行数值模拟,为选择超声速风洞收缩段的型线提供依据。基于特征线理论,利用解析法完成超音速喷管膨胀段型线设计,通过分析总压恢复系数及均匀度等流场参数,确定型线膨胀角角度及喷管长度。结果表明,收缩段型线选用双三次曲线,膨胀角度3.5°的情况下,超音速喷管出口达到了设计要求马赫数,并获得了较好的气流品质。