柴油机供油系统汽泡类型的研究

利用ＣＣＤ摄像机、高速Ａ／Ｄ卡、图像采集卡以及其它设备,对透明柴油机供油系统中的油汽两相流进行了研究,并对供油系统中的汽泡类型、汽泡运动规律和音速变化进行了阐述。试验结果表明,供油系统中汽泡的寿命会引起压力波形状的变化。同时,燃料供给系统参数的改变也会影响汽泡的运动速度,并使其运动轨迹发生变化,如直线运动、螺旋运动等     

静态闪蒸过程汽泡生长的理论与实验研究

本文针对去离子水静态闪蒸时单汽泡的动态生长过程开展了可视化实验观察及理论分析，研究了过热度和闪蒸腔压力对汽泡生长的影响。理论模型考虑了汽泡成核点附近固体壁面对汽泡生长的影响，通过与实验结果的对比表明，壁面效应对汽泡生长影响显著，尤其是汽泡生长速率较小时，引入壁面效应后的理论模型能更好的与实验结果相吻合。通过分析汽泡生长过程的动力学特征可知，相同闪蒸腔压力但过热度较大时，汽泡生长过程具有较短的表面张力控制阶段，并在过渡阶段和传热控制阶段均具有较大的生长速率；而相同过热度但较小闪蒸腔压力时，汽泡在早期的惯性控制阶段生长速率较小，但在后期的传热控制阶段生长速率较大。     

一种研究柴油机喷油系统中汽泡的新方法

介绍了一种研究柴油机喷油系统中汽泡的新方法－频谱分析法，通过对柴油机喷油系统中存在的不同汽泡类型时其压力波谱率结构特性的分析，作发现汽泡与频谱结构存在内在的联系，通过这种汽泡与频谱结构的内在联系，即可判断柴油机喷油系统中是否有汽泡存在。     

二甲醚燃料喷射过程的试验研究

系统研究了二甲醚 (DME)燃料的喷射过程 ,测试了不同工况下的油管泵端压力及嘴端压力、喷油器针阀升程和油管中燃料的音速。试验结果表明 :在供油提前角、转速和负荷相同的情况下 ,燃用二甲醚时油管泵端和嘴端压力的上升和下降速度、压力峰值都比燃用柴油时低 ;油管中 DME的音速远低于柴油 ;随着负荷的下降 ,DME的音速下降 ,且下降的速率远比柴油的大。与柴油相比 ,二甲醚的喷射延迟期和喷射持续期长 ,喷射始点的循环变动较大。     

不稳定蒸汽射流凝结振荡实验研究

对不稳定蒸汽射流凝结压力振荡现象进行了实验研究。结果表明:在不同的蒸汽质量流率和过冷水温度下蒸汽射流存在3种凝结流型,即喘振、半球形汽泡振荡和周期性汽泡振荡;压力振荡发生频率随着蒸汽质量流率的增加而增大,随着过冷水温度的升高先增大后减小,最大压力振荡发生频率出现在由喘振/半球形汽泡振荡区向周期性汽泡振荡区转变时;喘振和半球形汽泡振荡区的压力振荡幅值随蒸汽质量流率的增加而减小,周期性汽泡振荡区的压力振荡幅值随蒸汽质量流率的增加而增大;3种流型下的压力振荡幅值均随过冷水温度的升高而增大。     

出油阀弹簧刚度及开启压力对柴油机喷油系统中汽泡影响的研究

通过改变喷油泵出油阀弹簧刚度及开启压力 ,借助特制的透明出油阀紧帽腔、CCD摄像机、高速A/ D采集卡、图像采集卡和微型计算机等测试及处理设备 ,对喷油系统中的汽泡现象进行了试验研究 ,揭示出了出油阀弹簧刚度及开启压力对出油阀紧帽腔中汽泡数量和汽泡分布区域的影响规律     

柴油机燃油物性参数的研究

提出了燃油密度随压力和温度变化的综合经验公式，根据各参数间的严格关系推出了压缩率和音速的经验公式，并介绍了粘度的经验公式。试验结果表明，提出的经验公式具有较高的精度。     

在油—气两相流状态下柴油机喷油系统中压力波传播速度的研究

本文通过在喷油泵试验台上测定高压油路实际压力波传播速度，论述了在油－气两相状态下，柴油机喷没系统中高压油管和喷油嘴油道内音速的变化规律，并指出造成高压油路各段音速不同的原因是高压油路内气泡分布的不均匀性，特别值得注意的是，喷油嘴油内平均音速明显低于高压油管中的音速，这说明喷油嘴盛油槽内的气泡要多于高压油管中的气泡。     

在油－气两相流状态下柴油机喷油系统中压力波传播速度的研究

本文通过在喷油泵试验台上测定高压油路实际压力波传播速度，论述了在油一气两相状态下，柴油机喷油系统中高压油管和喷油嘴油道内音速的变化规律，并指出造成高压油路各段音速不同的原因是高压油路内气泡分布的不均匀性。特别值得注意的是，喷油嘴油道内平均音速明显低于高压油管中的音速，这说明喷油嘴盛油槽内的气泡要多于高压油管中的气泡。     

蒸汽蓄热过程单个汽泡的传热传质数值模拟

蒸汽蓄热器是一种高效的储存蒸汽热能的设备。从传热传质的角度,推导出蒸汽蓄热过程中单个高温蒸汽泡在低温连续液相中的汽泡半径比k和努赛尔数Nu的数学表达式。通过Mat Lab模拟出汽泡半径比k和努赛尔数Nu与汽泡上升速度U、汽泡初始半径R0和汽液两相温度差ΔT随时间的变化规律。研究表明,汽泡半径比k随着汽泡的上升逐渐减小。努赛尔数Nu随着汽泡的上升先减小后增大。在汽泡初始半径R0和汽泡上升速度U相同的工况下,存在一个最优汽液两相温度差ΔT,使得汽泡半径比k和努赛尔数Nu曲线下降最快。加快汽泡上升速度U、减小汽泡初始半径R0以及选择合适的汽液两相温度差ΔT,可以提高蒸汽蓄热过程的传热效率。     

汽车排气消声器内部声场的三维有限元分析

基于有限元理论,运用声学分析软件Sysnoise仿真分析扩张式消声器内部有、无气流存在时的声压分布特性和速度分布特性。结果表明：消声器在低频时,声波以一维平面波传播;在高频时,则以高次谐波形式传播;气流对消声器内部声压、速度分布有较大的影响。     

The unsteady fluctuating pressure and velocity in a cross flow fan

This paper investigates the relations between the fluctuating pressure and velocity of the source by means of nu- merical method and sound pressure in the far field obtained with an noise experiment for a novel cross flow fan. The frequency characteristics of the fluctuating pressure and velocity in a cross flow fan are analyzed by means of spectral analysis and wavelet transform. The fluctuating pressures obtained by large eddy simulation on the casing wall are compared with that of experiments and show good agreement. From the spectral analysis of sound source, it is found that the pressure fluctuating peak is correspond with the sound pressure in the far field.     

基于ARMA模型的变压器噪声逆向还原实验研究

基于声辐射理论和激光测振原理，通过实验测量干式变压器模型的表面振速和辐射噪声声压，分别采用表面振速法和频响函数法求得变压器的声辐射指数。在此基础上，采用自回归滑动平均（ARMA）模型开展变压器噪声逆向还原研究，获取声压与声压级预测值，并与实验值进行对比。结果表明：采用频响函数法得到的声辐射指数比采用表面振速法得到的约大1.0 ～ 1.5 dB；采用基于ARMA模型的噪声预测算法得到的声压与实验得到的声压约相差0.015 Pa，声压级约相差1 dB；利用基于ARMA模型的预测算法和激光测振原理进行噪声逆向还原具有较好的可行性，且可推广应用于其他结构辐射噪声的预测。     

Numerical modeling of two-phase supersonic ejectors for work-recovery applications

An ejector is a fluid pumping device that uses the energy of a high pressure motive fluid to raise the pressure of a secondary lower-pressure fluid. Motive pressure is converted into momentum through a choked nozzle creating a high velocity jet which entrains the surrounding low-momentum suction flow. The two streams mix and finally pressure is recovered through a diffuser. There has been little progress on high fidelity modeling of the expanding supersonic two-phase flow in refrigerant expansion work recovery ejectors due to rather complex physics involving nonequilibrium thermodynamics, shear mixing, and void fraction-dependent speed of sound. However, this technology can be applied to significantly increase the efficiency of space cooling and refrigeration devices. The approach developed in this study integrates models for real-fluid properties, local mass and energy transfer between the phases, and two-phase sonic velocity in the presence of phase change into a commercial CFD code. The intent is to create a practical design tool with better fidelity than HEM CFD models yet with tractability lacking in current boundary tracking phase change CFD models. The developed model has been validated through comparison of key performance metrics against test data under certain operating conditions.     

Effect of cavities inside tube banks on acoustic resonance

In the present paper the attention is focused on the effect of small cavities inside in-line tube banks on acoustic resonance which occurred in the two-dimensional model of boiler. We measured the sound pressure level, the amplitude and the phase delay of acoustic pressures and the gap velocity. As a result, we found many peak frequencies of sound pressure level with different Strouhal numbers, mainly about S1=0.15, 0.26 and 0.52. The variation of SPL for S,=0.26, 0.52 components in the tube banks with cavities was the same as the result of no cavities. The existence of cavities inside in-line tube banks caused the resonance of St=0.15. And the acoustic resonance of the first mode in the transverse direction was generated if the small cavities existed inside the tube banks. This resonance was not generated from the tube banks of no cavities. The resonance onset velocity in the transverse mode was fairly slower than that of no cavities. It was easy to generate acoustic resonance when there were small cavities inside in-line tube banks.     

Flow Induced Acoustic Resonance in In-line Tube Banks

In the present paper the attention is focused on the relation between vortex shedding phenomena andacoustic resonance which occurred in the two-dimensional model of boiler.There were tube bankswith in-line arrangement for small tube pitch ratio.We measured the sound pressure level,the phasedelay of acoustic pressures,the spectrum of velocity fluctuation and the gap velocity.As a result, wefound two peak frequencies of sound pressure level with different Strouhal numbers S_t,mainly about0.26 and 0.52.The noise of S_t=0.26 was the resonance of transverse mode and S_t=0.52 waslongitudinal mode.The vortex shedding of S_t=0.15 was generated inside the tube banks withoutacoustic resonance. As gap velocity increased, we observed that the peak level of spectrum was weakand broad-banded. The onset velocity of the acoustic resonance of longitudinal mode was lower thanthat of transverse mode.     

基于PIV测试的风轮主要声源区域雷诺应力特征分析

为了获悉风轮主要声源区域的流动机理,在风洞开口段,在不同风速和尖速比下,文章对风轮展向X/C=0.5区域不同相对弦长处的流场进行了PIV测试。测试结果表明:由于翼型表面发生流动分离导致流体速度脉动,雷诺应力迅速增加,使叶片与来流相互作用产生压力脉冲;随着相对弦长的增加,雷诺应力均有不同程度的增大,当X/C为0.4~0.8时,雷诺应力的变化最为明显;对比不同风速、尖速比、相对弦长处的雷诺应力数据发现,随着尖速比的增加,雷诺应力增大最明显的区域向前缘移动,流动分离位置提前,而风速变化对流动分离位置没有影响;发生流动分离后的主要声源区域的雷诺应力呈现单峰值,流体脉动程度较剧烈;对比不同工况下主要声源最大声压级和X/C=1处中心最大雷诺应力值发现,两者变化趋势一致且易受尖速比变化的影响。文章以实验测试的方法揭示了风轮主要声源区域雷诺应力表现的流动特征,研究成果对于叶片的优化设计和降噪方法的改进提供了可行的解决思路。