微重力气液两相环状流界面波特性分析

本文利用双重小波包分解算法,对微重力气液两相环状流界面波特性进行了分析,将实验测量到的环状液膜厚度信号分解成相干分量和非相干分量,并对相干信号与非相干信号的特征进行了分析,提出了一个新的描述微重力气液两相环状流界面波特性参数。     

倾斜下降管气液两相分层流截面含气率的计算与液层高度的预测

分层流是气液两相流中常见的流动型式，分层流中液层高度是计算的基本数据，由于界面波的存在，对液层的测量和预测都很困难．Ｖｌａｃｈｏｓ提出了预测气液两相分层流液层厚度的关系式，但这一关系式并不适用于倾斜下降管气液两相流．本文提出了计算倾斜下降管气液两相分层流截面含气率的理论模型，在这种模型下得到的截面含气率和实验结果符合良好．在大量实验的基础上，考虑了倾角、管径、气液各相折算速度的影响，根据实验数据提出了预测液层厚度的关系式。     

空隙率波的波速与气相漂移特性研究

针对垂直上升管内气-水两相泡状流,利用高速数字摄像技术、电导探针和相关性原理,测量了不同气液表现流速下泡状流空隙率波的传播速度,分析了不同扰动频率对空隙率波瞬时波速概率分布的影响,研究了空隙率波的传播相对于两相混合流速的漂移特性．研究结果表明,空隙率波的传播相对于两相混合流速呈正漂移,且飘移速度略大于气相的飘移速度,随两相流混合流速的增大呈线性增大．     

气液团状流内界面波运动模型研究

为了揭示团状流中夹带液滴的产生机理,本文建立了气液团状流内界面波运动模型。该模型可以预测界面波沿壁而的运动规律及界面波特性(波幅、波速)的变化特点,理论解释团状流扰动性大的特点。结果表明:当气速较小或液速较大时,界面波在运动过程中存在反转现象,当进入环状流时,反转现象消失。界面波波速与最大波幅均随气、液速度的增大而增大,而临界波幅主要受气速的影响。通过与实验结果对比,证明该模型可以较好地反映界面波在团状流条件下的运动特点。     

小管径气液两相流空隙率波传播的多尺度相关性

空隙率波是气液两相流系统的特殊物理现象,理解空隙率波的传播特性对揭示两相流流型转变与流速测量物理机理具有重要意义.本文首先考察了典型非线性系统的多尺度互相关特性,发现去趋势互相关分析方法可有效揭示系统的多尺度非线性动力学特征;然后,通过采集垂直上升小管径气液两相流电导传感器阵列上下游空隙率波动数据,提出采用多尺度去趋势互相关分析方法探测空隙率波传播的多尺度互相关特性,并提取了低尺度空隙率波互相关水平增长率;另外,通过计算空隙率波空间衰减因子,考察了气液两相流空隙率波传播的结构不稳定行为.结果表明,空隙率波结构的多尺度互相关特性与其空间衰减特性具有较好的物理关联性:对于气液两相流过渡流型,低尺度空隙率波互相关水平增长率较高,且与较为稳定的空隙率波传播特性相对应;而当气液两相流空隙率波明显衰减或放大时,空隙率波互相关水平增长速率一般较低.     

ρ-VOF:一种可清晰模拟自由界面的两相流方法

文章通过对EFM(effective field modeling)模型进行简化, 消除了原模型的非守恒性项和非双曲性特性项, 发展了一种基于密度的气液两相流模拟方法: ρ-VOF方法.利用体积分数信息对控制单元内的自由界面进行重构, 得到了控制单元内流体的空间分布, 并采用AUSM+-up格式获得考虑气液流体接触间断信息的对流通量.新方法可统一处理激波间断和接触间断的相互作用, 保持自由界面的尖锐性, 并且其计算量与自由界面的空间复杂度无关.最后, 数值模拟了液体激波管气液激波管和气体激波跨二维液滴传播等问题, 并与文献结果进行对比, 验证了本方法在气液两相流模拟中的准确性.      

泡状流局部界面浓度实验与理论研究

应用高速数字摄像系统,首先对双头电导探针测量泡状流局部界面浓度的几种模型进行了标定和评价。使用标定好的双头电导探针技术,对垂直上升管内气液两相泡状流局部界面浓度和含气率分布特性进行了深入的实验研究。试验段为内径40 mm的透明有机玻璃管。根据试验数据的分析结果,发展了一种垂直上升管内气液两相泡状流局部界面浓度预测模型。在本文实验条件下,该局部界面浓度模型预测结果能够与实验数据很好地符合。     

气液两相流压力波色散特性实验研究

设计了可调频式压力扰动源的气液两相流压力波实验装置,实验研究了垂直上升管内气液两相流泡状流、弹状流压力波的色散规律。实验结果表明,对泡状流,在实验范围内,压力波的传播速度及其衰减跟扰动频率有关,随着扰动频率的增加,波速及其衰减都增加;工质的流速对压力波的色散特性没有影响。结合数值模拟结果,验证了泡状流压力波色散特性的临界频率现象,即高于临界频率,压力波色散特性消失,本文分析了相应的物理机制。对弹状流,压力波同样具有典型的色散特性,已有研究结果还不能预测其色散规律。     

水平微圆管内环状流气液界面不稳定性分析

本文以水平微圆管内气液两相环状流气液界面为研究对象,通过分析重力、表面张力和界面剪切力对环状流液膜厚度的影响,重点考虑Rayleigh不稳定性对气液界面的依存关系,得到了不同管径和气核直径变化时不稳定性的变化规律,并分析拟合了最危险波长和气核直径的关联式,为后续建立高热流密度条件下微通道内强化传热理论模型奠定基础.     

基于PSD原理的小管道两相流参数光学测量

针对小管道两相流参数测量问题,本文提出了一种基于PSD工作原理的光学测量新方法。该方法利用两相弯曲界面使光路发生偏转的特性,根据光电池输出信号判断相界面两侧的相分布情况和两相流的流动方向等信息。实验结果表明,该新方法可用于小管道气液两相流的研究,是一种有效的小管道两相流参数测量手段。     

Analysis of Second-Harmonic Generation of Low-Frequency Dilatational Lamb Waves in a Two-Layered Composite Plate

We analyze the effect of second-harmonic generation(SHG) of primary Lamb wave propagation in a two-layered composite plate, and then investigate the influence of interfacial properties on the said effect at low frequency. It is found that changes in the interfacial properties essentially affect the dispersion relation and then the maximum cumulative distance of the double-frequency Lamb wave generated. This will remarkably influence the efficiency of SHG. To overcome the complications arising from the inherent dispersion and multimode natures in analyzing the SHG effect of Lamb waves, the present work focuses on the analysis of the SHG effect of low-frequency dilatational Lamb wave propagation. Both the numerical analysis and finite element simulation indicate that the SHG effect of low-frequency dilatational Lamb wave propagation is found to be much more sensitive to changes in the interfacial properties than primary Lamb waves. The potential of using the SHG effect of low-frequency dilatational Lamb waves to characterize a minor change in the interfacial properties is analyzed.     

有流存在时三层流体界面波的二阶Stokes波解

以小振幅波理论为基础，利用摄动方法研究了有背景流场存在时密度三层成层状态下的界面内波，得到了各层流体速度势的二阶渐近解及界面内波波面位移的二阶Stokes波解，并讨论了界面波的Kelvin-Helmholtz不稳定性.结果表明：有流存在的情况下三层密度成层流体界面内波的一阶渐近解(线性波解)、频散关系及二阶渐近解不仅依赖于各层流体的厚度和密度，也依赖于各层流体的背景流场；界面内波波面位移的二阶Stokes波解不仅描述了界面波之间的二阶非线性相互作用，也描述了背景流与界面波之间的二阶非线性相互作用；当每层流 关键词： 界面波 均匀流 二阶Stokes波解 Kelvin-Helmholtz不稳定性     

Guided waves in a stratified half-space

The dispersion and excitation mechanisms and the energy distribution of guided waves in a stratified half-space are studied. All possible guided waves excited by a symmetric point source in two or three-layer medium models and their relation to the medium parameters are analyzed in detail. The excitation and propagation characteristics, as well as the energy distribution along the depth direction, of all modes of the surface waves and trapped waves are numerically investigated and analyzed thoroughly not only in the case when the shear wave velocity increases from up to down layers but also when a low-velocity layer is contained in halfspace, especially when the shear wave velocity decreases from up to down layers. It is found that there exist many guided wave modes in the case where the shear wave velocity of each layer increases from up to down layers. However, there is less than one guided wave mode in the case where the shear wave velocity of each layer decreases from up to down layers. The trapped waves exist and propagate along the low-velocity structure in the stratified half-space. It is also found that the characteristic of a mode is related to the source frequency. It is possible that a surface wave at one value of frequency is like a trapped wave at another value of frequency. Finally, the relation of the characteristics of all guided waves (surface waves and trapped waves) to the parameters of media is studied.     

用VOF法数值模拟孤立波迎撞及在后台阶上的演化

通过数值离散求解二维Navier-Stokes方程和利用VOF界面跟踪技术,分别对两个界面孤立波之间的迎撞问题和一个孤立波在后台阶地形上的演化问题进行数值模拟。     

Third-order Stokes wave solutions for interfacial internalwaves in three-layer dendity-stratified fluid

<正>Interfacial internal waves in a three-layer density-stratified fluid are investigated using a singular perturbation method,and third-order asymptotic solutions of the velocity potentials and third-order Stokes wave solutions of the associated elevations of the interfacial waves are presented based on the small amplitude wave theory.As expected,the third-order solutions describe the third-order nonlinear modification and the third-order nonlinear interactions between the interfacial waves.The wave velocity depends on not only the wave number and the depth of each layer but also on the wave amplitude.     

Dispersion characteristics of surface magnetostatic waves with dissipation

It is shown that unlike undamped waves, the dispersion characteristics of spin surface waves with dissipation have a maximum wave number at which there is a downward reversal in the dispersion curve of a wave number. This forms the upper branch of a dispersion curve with inverse dispersion and high attenuation, leading to an unclear frequency dependence of the wave vector. The lower primary dispersion branch corresponds to waves with forward dispersion, and attenuation is proportional to the small parameter of dissipation. However, the coefficient of wave attenuation grows sharply near the maximum wave number. Some angular and frequency limits of surface wave propagation change as well.     

Visualization of transient interfacial waves induced by spin-up of two immiscible fluid layers

Abstract  

Interfacial waves of two immiscible layers in a spin-up container were investigated using experimental visualization. While the interface near the central part rose up, instability waves propagated in an azimuthal direction on the interface. These waves were mainly caused by Kelvin–Helmholtz instability for the velocity difference between two layers during spin-up, but had complicated transient characteristics owing to the rotation in a closed system. We visualized the structure of the interfacial waves by the use of three types of optical characteristics of the interface. Image processing provided the detailed factors of the interfacial waves that were classified in four life stages from their generation to disappearance. The initial generation process involved many frequency modes due to a large velocity difference, and then a low mode stood out during the growth, and disappeared with an ellipsoidal sloshing mode to achieve the rigid rotation in both layers.     

Study on frequency optimization and mechanism of ultrasonic waves assisting water flooding in low-permeability reservoirs

Water flooding is one of widely used technique to improve oil recovery from conventional reservoirs, but its performance in low-permeability reservoirs is barely satisfactory. Besides adding chemical agents, ultrasonic wave is an effective and environmental-friendly strategy to assist in water flooding for enhanced oil recovery (EOR) in unconventional reservoirs. The acoustic frequency plays a dominating role in the EOR performance of ultrasonic wave and is usually optimized through a series of time-consuming laboratory experiments. Hence, this study proposes an unsupervised learning method to group low-permeability cores in terms of permeability, porosity and wettability. This grouping algorithm succeeds to classify the 100 natural cores adopted in this study into five categories and the water flooding experiment certificates the accuracy and reliability of the clustering results. It is proved that ultrasonic waves can further improve the oil recovery yielded by water-flooding, especially in the oil-wet and weakly water-wet low-permeability cores. Furthermore, we investigated the EOR mechanism of ultrasonic waves in the low-permeability reservoir via scanning electron microscope observation, infrared characterization, interfacial tension and oil viscosity measurement. Although ultrasonic waves cannot ameliorate the components of light oil as dramatically as those of heavy oil, such compound changes still contribute to the oil viscosity and oil-water interfacial tension reductions. More importantly, ultrasonic waves may modify the micromorphology of low-permeability cores and improve the pore connectivity.     

Potential surface waves at the boundary of a metal with a magnetoactive plasma at finite pressure

The propagation of surface-type potential waves along the interfacial boundary of a plasma with an ideally conducting metal in an external magnetic field perpendicular to the boundary is examined. It is shown that a necessary condition for the existence of these waves in the system is a finite gas kinetic pressure. Dispersion relations for these waves and expressions for the penetration depth of the wave fields into the plasma are obtained, and they are studied numerically for various plasma parameters. The frequency region for propagation of these waves is found. It is also shown that in a nonzero external magnetic field a system of this kind has a range of frequencies in which the wave is a generalized surface wave. Zh. Tekh. Fiz. 69, 30–33 (November 1999)     

电磁波在无回波室中物理现象的分析计算

本文讨论了无回波室中,吸收材料对电磁波吸收和反射、极化偏转、多波干涉以及由于干涉而形成复杂的驻波分布,文中以直射波为参考波束,只考虑在直射波极化方向上各反射波的场分量,从而给出了多波干涉情况下的场强、反射电平、交叉极化特性、通路损耗均匀性的表示式以及用于工程设计的固有反射电平计算曲线,最后,给出了部分典型实验结果。 关键词：