液体射流的非轴对称破碎

本文分析粘性液体射流的线性稳定性问题，本文首次根据理论预测所确定的物理条件观察到了射流在各种非轴对称模式支配下的破碎情况，实验采用的是高速公路分幅激光全息技术，实验结果表明，液体射流结构遵守稳定性理论所预测的规律，实验还发现，液体射流的实际破碎尺寸要大于线性稳定必伯预测结果。     

高速液体射流初始阶段的破碎

采用激光分幅全息技术观察到了直径０．４ｍｍ液体射流上的表面波从小到大，最后导致液体破碎的发展过程，本所得的基本结论是：液体在雾化初始阶段的破腑起因于扰动波，扰动波由表及里，在周向与轴秒不断发展，首先将射流撕裂成大液滴，之后再进一步破碎成小液滴。液体射流破碎后的液滴尺寸往往大于初始扰动波长。     

高速粘性液体射流的不稳定模式

本利用线性不稳定性理论研究了高速粘液性射流的破碎问题，并利用先进的高速分幅全息摄影技术首次比较系统地观察了几种不稳定模式的表明形态，实验观察结果与理论预测基本一致。研究结果表明，在适当的条件下，非轴对称模式也有可能成为最不稳定模式，从而肯定了非轴对称模式在射流破碎中的重要作用。     

受激液体射流的非轴对称模式

利用液体射流破碎的线性不稳定性理论,研究了受激液体射流特有的“局部频段非轴对称模式占优”现象,由一系列理论计算结果,得到了Re-We平面上的相应临界曲线,并根据这些曲线得出了受激液体射流出现非轴对称模式结构特征的物理条件。计算结果还表明,受激液体射流和自由液体射流的临界曲线有明显不同。初步的实验观察结果证实了理论的预测。     

可压缩气体中的三维黏性液体射流雾化机理

建立了可压缩气体中的三维黏性液体射流雾化数学模型,在射流雾化过程中起控制作用的参数主要有气液速度、气液密度、气液界面表面张力、液体黏性、喷嘴直径及音速.采用线性空间稳定性分析方法详细分析了这些参数在高速射流雾化过程中不稳定性的作用.结果是：增加液体射流速度、气体密度及喷嘴直径;减少液体密度、液体黏性及表面张力,可使射流不稳定性增强.此外,当气流与液体射流反向时增加气体流速也可以使流动不稳定性增强,但当气流与液体射流同向时结果相反.气体可压缩性的增加使流动变得不稳定,但它的影响是很小的.     

脉冲液体射流泵能量损失分析

研究了脉冲液体射流泵的能量损失与其基本方程式间的关系,给出了脉冲液体射流泵主要流动部件的能量损失压力比的表达式,系统分析了流动部件的能量转化与能量损失及其对脉冲液体射流泵基本性能的影响,并与恒定液体射流泵的基本性能进行了比较,沟通了两者间关系,分析了产生能量损失的主要因素,提出未来应深入研究优化脉冲液体射流泵参数.     

同轴旋转可压缩气流中黏性液体射流形态研究

采用射流线性稳定性分析方法,考虑液体黏性、周围气流的同轴旋转运动以及可压缩性的条件下,建立了描述同轴旋转可压缩气流中黏性液体射流的数学模型,并进行了验证,研究了气流量纲为1旋转强度以及流体物性对液体射流不稳定形态的影响．研究表明：周围气流的旋转速度较小时,对射流起促稳作用,继续增大气流量纲为1旋转强度,开始对射流起促分裂作用;且随着气流旋转强度的增大,射流扰动沿周向方向发展,射流柱变的高度不对称．在研究参数范围内,气体可压缩性和气/液密度比均能促进射流的失稳,并会影响射流空间形态,尤其是在周向方向上能够改变射流的占优模式,增强射流的不对称性;液体黏性以及表面张力对射流均具有增强稳定性的作用．     

脉冲液体射流泵性能的研究

为获得脉冲液体射流泵性能方程中各参数对其性能的影响规律,用数值计算的方法对脉冲液体射流泵的基本性能方程进行了系统的研究,得出了脉冲射流主要是提高射流泵的卷吸率的结论。定量分析了喉管流速系数和喉管进口段的流速系数等参数的变化规律及其对性能的影响程度,进一步探明了其内部流动规律,对设计性能优良的射流泵具有理论指导意义。     

液体射流泵喷嘴长径比的数值分析

液体射流泵的工作喷嘴一般采用锥直形喷嘴,锥直形喷嘴出口直段的长度与喷嘴出口直径之比即喷嘴长径比,是射流泵的重要几何参数。为了研究喷嘴长径比对液体射流泵性能的影响,采用Realizableκ-ε模型对不同长径比的射流泵内部流动进行三维数值模拟。结果表明,在射流泵的流量比小于0.5时,不同喷嘴长径比所对应的射流泵效率曲线差别不大;在流量比大于0.5时,以射流泵效率为判据,喷嘴长径比范围为0.250～1.000的射流泵性能较好;不同喷嘴长径比对应的射流泵壁面剪切应力相差不大。从湍流耗散率、喷嘴出口断面收缩、核心区长度等方面考虑,喷嘴长径比范围为0.250～1.000的射流泵性能较好。     

气体旋转运动对环膜液体射流不稳定性影响的研究

环膜液体射流的破碎机理研究对于GDI汽油机的雾化过程具有重要的意义。利用线性不稳定性理论研究了旋转气体运动对低阶和高阶模式黏性环膜液体射流破碎的影响。对于色散方程的数值计算结果表明,无论是对称模式还是非对称模式,低阶模式的扰动增长率通常较之高阶模式要大得多,但较之低阶模式扰动,高阶模式对气体旋转运动更为敏感。研究结果同时表明,对于非对称模式,无论是低阶模式还是高阶模式的扰动,气体旋转运动都是液体破碎的失稳因素;对于对称模式,气体旋转运动是低阶模式扰动的促稳因素,然而却是高阶模式扰动的强烈的失稳因素。     

Theoretical Analysis of Hydraulic Jump on Extremely Small Size Liquid Jet Impingement

INTR0DUCTI0NWhenliquidjetsverticallyimpingeonahorizontalplane,theliquidspreadsoverthesurfaceasathinlayerboundedbyahydraulicjumpbeyondwhichthedepthoftheliquidismuchgreater.Totheauthor'sknowledge,thehydraulicjumphasbeenprovedtooc-curwheneverthefilmspreadsfarenough.Itischarac-terizedbyasignificantreductioninfilmaverageveloc-ityandacorrespondinglysharpincreaseintheliquidfilmthickness.Asinallconvectiveheattransfersituations,theflowfieldofanimpingingliquidjetcontrolstheheattransfercharacteristic…     

往复炉启炉过程基本特征及节能初探

对间歇运行的往复炉启炉过程的燃烧工况及负荷工况进行了实测和曲线分析,将启炉过程划分为启炉、过渡和稳定三个阶段,分析了各阶段的基本特点,对提高锅炉的使用效果和节约能源乃至对间歇供热问题的研究都有重要意义。     

BH175F1涡流室式柴油机工作过程的数值模拟

为改善湖南新滨湖发动机有限公司的BH175F1型单缸风冷涡流室式柴油机的性能,利用AVL-FIRE程序对其缸内工作过程进行了数值模拟研究。研究结果揭示了燃烧室内的平均温度和压力的变化,涡流室内一次涡流、二次涡流的形态和位置等相关信息,以及燃油喷雾扩散和混合气形成过程的特点。此外,还探讨了油嘴安装角度对混合气形成及燃烧过程的影响,发现了油嘴安装角度偏离对称面可以获得更加均匀分布的混合气,确定了可以使燃烧持续期缩短将近5°CA的油嘴安装角度。     

运行工况对基础燃料均质压燃燃烧过程影响的试验研究

在一台经改装的单缸直喷式柴油机上进行了不同辛烷值基础燃料下发动机转速对均质压燃（HCCI）燃烧特性、工况范围和排放特性影响的试验研究。研究结果表明：发动机转速升高,不同辛烷值燃料着火燃烧时刻推迟,以曲轴转角计算的燃烧持续期延长,高辛烷值燃料的缸内最大爆发压力和缸内温度降低;在中间转速,HCCI实现的最高平均指示压力最大,高转速工况,最高平均指示压力降低;对于低辛烷值燃料,转速对燃烧效率影响不大,转速升高,指示热效率增大;对于高辛烷值燃料,转速升高燃烧效率降低,指示热效率在中间转速最高,高转速降低。排放测试表明,转速升高使得HCCI运转的HC和CO排放都升高,NOx排放则逐渐降低。     

Experimental study of turbulent jet induced by steam jet condensation through a hole in a water tank

A turbulent jet induced by steam jet condensation in a water pool was investigated experimentally. An experimental apparatus equipped with a steam boiler, a single-hole steam sparger, and a water pool, etc. was used. For the measurements, a pitot tube and thermocouples were used for turbulent flow velocity and temperatures, respectively. Overall flow shapes of the turbulent jet by the steam jet condensation are similar to those of axially symmetric turbulent jet flows. The angular coefficients of turbulent rays are quantitatively comparable between the traditional turbulent jet flows and the turbulent jet flows induced by the steam jet condensation in this work. Although the turbulent flows were induced by the steam jet condensation, general theory of turbulent jets was found to be applicable to the turbulent flows of this work.     

Numerical simulation on the behavior of a liquid jet into an air flow

A numerical simulation has been performed to clarify the effects of turbulence in a liquid on the deformation of the liquid jet surface into an air flow. The turbulences in the liquid jet were simulated by the Rankin vortices, and the liquid jet surface was tracked numerically by the volume of fluid method. By numerical simulations, the onset of the protrusions on the liquid jet surface is caused by the vortices in the liquid, and the surrounding air flow plays an important role in the amplification of the protrusions. The amplification rate of the trough displacement is proportional to the air‐to‐liquid velocity ratio. At large imposed vortex intensities, the trough displacement increases with the vortex intensity. On the other hand, at small imposed vortex intensities, the amplification of the trough displacement is also affected by factors other than vortex intensity. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 473–484, 2001     

Stability of an annular viscous liquid jet in compressible gases with different properties inside and outside of the jet

A spatial linear instability analysis is conducted on an annular viscous liquid jet injected into compressible gases and a three-dimensional model of the jet is developed. The model takes into account differences between the velocities, densities of the gases inside and outside of the liquid jet. Theoretical analysis reveals that there exist 9 dimensionless parameters controlling the instability of the liquid jet. Numerical computations reveal some basic characteristics in the breakup and atomization process of the liquid jet as well as influences of these relevant parameters. Major observations and findings of this study are as follows. The Mach number plays a destabilizing role and the inner Mach number has a greater effect on the jet instability than the outer Mach number. The Reynolds number always tends to promote the instabilities of the liquid jet, but its influence is very limited. The Weber number and the gas-to-liquid density ratio also have unstable effects and can improve the atomization of liquid jets. Furthermore, the effects of the Weber number and gas-to-liquid density ratio on the maximum growth rates of axisymmetric and non-axisymmetric disturbances and corresponding dominant wave numbers are manifested in a linear way, while that of the Mach number is non-linear. The effect of Reynolds on the maximum growth rates is non-linear, but the dominant wavenumber is almost not affected by the Reynolds number.     

液体燃料射流最不稳定频率的理论分析（1）——液体燃料射流的最不？…

利用线性不稳定性理论,对粘性液体燃料射流射入气体介质的射流模型所对应的色散方程进行了数值求解。利用计算结果,分析了液体燃料射流不稳定性研究中的３个最重要的无量纲参数参韦韦伯数Ｗｅ、雷诺数Ｒｅ及密度比Ｑ,对分别处于瑞利模式和泰勒模式下的液体射流的最不稳定频率及对应的最大扰动增长率的影响。     

Analysis of jet flames and unignited jets from unintended releases of hydrogen

A combined experimental and modeling program is being carried out at Sandia National Laboratories to characterize and predict the behavior of unintended hydrogen releases. In the case where the hydrogen leak remains unignited, knowledge of the concentration field and flammability envelope is an issue of importance in determining consequence distances for the safe use of hydrogen. In the case where a high-pressure leak of hydrogen is ignited, a classic turbulent jet flame forms. Knowledge of the flame length and thermal radiation heat flux distribution is important to safety. Depending on the effective diameter of the leak and the tank source pressure, free jet flames can be extensive in length and pose significant radiation and impingement hazard, resulting in consequence distances that are unacceptably large. One possible mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. The reasoning is that walls will reduce the extent of unacceptable consequences due to jet releases resulting from accidents involving high-pressure equipment. While reducing the jet extent, the walls may introduce other hazards if not configured properly. The goal of this work is to provide guidance on configuration and placement of these walls to minimize overall hazards using a quantitative risk assessment approach. The program includes detailed CFD calculations of jet flames and unignited jets to predict how hydrogen leaks and jet flames interact with barriers, complemented by an experimental validation program that considers the interaction of jet flames and unignited jets with barriers.     

The effect of turbulent jet induced by pre-chamber sparkplug on combustion characteristics of hydrogen-air pre-mixture

Effect of turbulent jet ignition induced by pre-chamber sparkplug (PCSP), a simper version of turbulent jet ignition pre-chamber system without fuel injection, on the air-hydrogen combustion characteristics was conducted based on an optical constant volume chamber under varied equivalence ratio conditions. The dynamic pressure sensor and schlieren system were used to evaluate the heat release and flame propagation characteristics. The results confirm the feasibility of PCSP type turbulent jet. The jet increase the flame propagation speed significantly compared to standard ignition, which shorten ignition delay and combustion duration, advance T50 largely, and increase the maximum combustion pressure slightly. As a result, the combustion intensity is increased largely, especially under lean regime, the combustion intensity index can be as high as 1.7 at certain equivalence ratio. In addition, the PCSP turbulent jet reduces the sensitivity of heat release to variation of equivalence ratio, which is helpful to simplify the combustion controlling strategy. Furthermore, with the enhancement of the flame propagation, the tendency of knocking combustion can be suppressed potentially.