垂直向下管内两相流泡状-弹状流型转换研究

建立实验系统,在维持管道出口压力为0.2MPa的条件下,对内径分别为15mm、25mm、40mm、65mm的垂直向下管内空气-水气液两相流动进行了实验研究,获得了两相流泡状-弹状流型分布。实验研究发现:管径对于泡状流与弹状流流型特征有较大影响,并且进一步影响流型转换边界,随着管径增加,泡状流-弹状流的流型转换边界向折算气速减小的方向移动。基于理论推导及实验数据,建立了垂直向下管内气液两相流泡状流-弹状流流型转换预测模型,该模型对本文实验工况条件下的垂直向下管内空气-水气液两相流流型转换具有良好的预测效果,预测模型的计算结果与实验数据之间的误差小于10%。     

多相流水击模型在泄压阀压力精度设定中的应用

为了有效地指导氮气式水击泄压阀的压力精度设定工作,提出了理论方法。该方法根据动量守恒定理与动力学理论,通过对油-气-水三相流的运动状态与泄压阀阀芯的受力进行分析,构建了油-气-水三相流水击模型和阀芯运动力学模型;设计了油-气-水三相流水击试验方案并进行了试验。结合MATLAB/Simulink仿真模拟结果与试验数据进行对比,结果表明:构建的数学模型能准确地计算出符合实际工况的水击压强、氮气压力、弹簧力的理论数值;氮气压力、弹簧力、水击压强的大小呈周期性变化,且变化周期基本同步;水击压强可进一步确定氮气压力、弹簧力的设定数值,解决了泄压阀的压力精度设定问题。     

非牛顿体通用模型线接触弹流润滑的数值分析

基于润滑剂在弹流润滑状态下表现为非牛顿体特性,根据弹流润滑理论,采用一种新的非牛顿体流变模型,建立了适用于非牛顿体的修正Ｒｅｙｎｏｌｄｓ方程,进行了等温弹流润滑的数值计算,并在等温解的基础地温度场分析。数值分析结果表明,由于滑滚比和模型参数对剪应力影响较大,因而在滑滚比和模型参数较大时应进行热弹流计算。通过温度场分析可证明：非牛顿体通过模型可用于等温弹流润滑和热弹流润滑计算。     

直升机旋翼气弹动力学优化策略(Ⅰ)——灵敏度分析技术研究

基于旋翼气弹动力学模型以及摄动法的灵敏度分析和直接解析的链式规则灵敏度分析相结合技术,推导了直升机旋翼气弹动力学的气弹稳定性、模态频率、自转惯量、桨叶质量、桨叶动应力等参数的灵敏度计算过程。通过算例计算结果表明:使用灵敏度分析方法与直接优化相比,实现动应力减少1.2%,质量减少0.84%,优化时间缩短2.73倍;该灵敏度分析技术对于直升机旋翼气弹动力学优化设计收敛的速度和优化结果效果明显。     

用Laplace变换分析弹—粘塑性梁的弯曲

在弹塑性梁弯曲变形理论基础上，本文用Ｌａｐｌａｃｅ变换进一步分析了弹－粘塑性梁的弯曲问题。并以矩形截面梁为例，说明弹－粘塑性梁弯曲时的弹性与粘塑性区的应力，梁的度及弹－粘塑性交线的计算。     

对基于恢复时间的剪稀流变模型的进一步探讨及其对squalane油品流变特性的模拟

本文作者前期基于球-杆变形后恢复到原状态的时间,建立了新的形式较简单的流变模型,并模拟了黏度较高的聚合油PAO 650的摩擦系数曲线.本文中将该模型的应用范围进行了推广,模拟了黏度较低的squalane油品的流变特性.把该流变公式应用到点接触热流变弹流润滑的数学模型中,通过与试验测得的摩擦系数的比较确定了使用该模型时squalane油品的待定参数值,进而得到了点接触热流变弹流润滑的完全数值解.结果表明:解得的压力、膜厚和温度的变化规律均符合预期,且摩擦系数曲线与试验结果整体吻合性较好.新流变模型对高、低黏度的油品均能得到合理的流变特性曲线,说明作者的基于恢复时间的流变模型具有一定的正确性和可应用性.另外,由新模型计算得到的squalane油品的剪应力曲线呈现出一近似水平段,这也在一定程度上解释了流变试验文献中多次提到的极限剪应力现象.     

水平管气液两相间歇流含气率研究

对大直径水平管内气液二相流动进行了实验，实验结果表明大直径水平管与小直径水平管具有不同的气液二相流动特征。分析和提出了适用于大直径水平管内间歇流液弹含气率模型，其计算值与实验值非常接近。     

预紧方式对弹流润滑下角接触球轴承内部力学特性的影响

油膜厚度预测在评估弹流润滑(EHL)下角接触球轴承的性能和耐久性方面发挥着重要的作用. 耦合拟静力学理论和自旋下椭圆接触弹流模型,以干接触角接触球轴承拟静力学分析方法为基础,建立了定压和定位预紧方式下考虑弹流润滑和钢球自旋运动的角接触球轴承的拟静力学分析模型. 采用快速傅里叶变换(FFT)计算椭圆接触的弹性变形,运用Gauss-Seidel迭代方法求解Reynolds方程,得到自旋弹流模型的完全数值解,将其代入轴承拟静力学模型中迭代,得到轴承内部接触载荷、三维接触压力及三维膜厚分布. 对采用不同预紧方式的SKF7210型角接触球轴承进行分析,结果表明:富油润滑下,当轴承转速从0增大到15 000 r/min时,定压预紧时内圈轴向位移减小17.83%,而定位预紧时内圈承受的轴向载荷增大23.17%;定压预紧方式下球与内外滚道间膜厚均略大于定位预紧. 此外,不同预紧方式下,外圈上的中心膜厚大于内圈10%. 与干接触相比,定压下考虑弹流润滑内圈上接触载荷略大0.64%.      

管壳式换热器内气液两相流冲刷垂直管束的阻力特性研究

本文对垂直布置的管壳式换热器中，气液两相流冲刷管束时的流动阻力进行了实验研究。实验段采用管壳式换热器模型，其圆形外壳内的管束由４９根管子组成，并沿长度方向用三块折流板将管束分成四个冲刷流程。当气液两相流自下而上冲刷管束时，分别测量摩擦阻力和局部阻力，并用分相流动模型进行分析，得到良好的计算关联式。     

渐开线斜齿轮非稳态弹流润滑数值模拟研究

建立了渐开线斜齿轮啮合的弹流润滑计算模型,将斜齿圆柱齿轮啮合的齿面接触等效为有限长线接触的弹流润滑问题.考虑斜齿轮啮合的实际因素,将斜齿轮啮合过程中的等效曲率半径和齿面载荷的变化反映到弹流润滑计算模型中,应用统一Reynolds方程方法求得轮齿在1个完整啮合周期内的瞬时弹流润滑数值解.结果表明：斜齿轮啮合线上各点处的膜厚、压力均有较大不同,各接触点处的油膜厚度受综合曲率半径的影响较大;斜齿轮传动非稳态效应相对较弱;小齿轮齿根附近和节点位置处润滑状态较差;适当增大压力角可以改善齿轮的润滑.     

An Experimental Study of Mobilization and Creeping Flow of Oil Slugs in a Water-Filled Capillary

An experimental investigation was carried out on mobilization and very slow flow of oil slugs in a capillary tube. The pressure drop of the slug flow was measured at every stage of mobilizing and moving the oil slugs as a function of capillary number in the range of 4 × 10⁻⁷–6 × 10⁻⁶. The pressure drop across the oil slug experienced three stages: build-up, hold-up, and steady stages. During the build-up stage, the convex rear end of the slug was becoming concave into the oil slug and the convex front end of the slug moved ahead to form a new portion of the slug. At the hold-up stage, both the concave rear end and the front end continued to advance, and the initial contact line of the oil slug with the tube wall through a very thin water film was being shortened. At this stage, the pressure drop reached a maximum value and remained nearly constant. At the steady stage, after the oil slug was completely mobilized out of the original contact region, the differential pressure had a step-drop first, and then the oil slug flowed at a lower differential pressure depending on the flow rate. Numerous slug flow tests of this study showed that the hold-up pressure drop was always higher than the steady stage pressure drop. Results also showed that the measured extra pressure drop was significantly high compared to the pressure drop calculated from Poiseuille equation, which is still commonly used in network modeling of multiphase flow in porous media.     

Pressure drop in two phase slug/bubble flows in mini scale capillaries

A segmented two phase slug/bubble flow occurs where a liquid and a gas are pumped into the same tube over a range of Reynolds numbers. This segmented two phase flow regime is accompanied by an increase in pressure drop relative to the single phase flow where only one fluid is flowing in a capillary. This work experimentally and theoretically examines the pressure drop encountered by the slug/bubble flow with varying slug lengths in mini channels. In the experimental work the dimensionless parameters of Reynolds number and Capillary number span over three orders of magnitude, and dimensionless slug length ranges over two orders of magnitude to represent flows typical of mini- and micro-scale systems. It is found, in agreement with previous work, that these dimensionless groups provide the correct scaling to represent the pressure drop in two phase slug/bubble flow, although the additional pressure drop caused by the interface regions was found to be ∼40% less than previously reported.     

Influence of gas injection on phase inversion in an oil–water flow through a vertical tube

An experimental study has been made of the influence of gas injection on the phase inversion between oil and water flowing through a vertical tube. Particular attention was paid to the influence on the critical concentration of oil and water where phase inversion occurs and on the pressure drop increase over the tube during phase inversion. By using different types of gas injectors also the influence of the bubble size of the injected gas on the phase inversion was studied. It was found that gas injection does not significantly change the critical concentration, but the influence on the pressure drop is considerable. For mixture velocities larger than 1 m/s, the pressure drop over the tube increases with decreasing bubble size and at inversion can become even larger than the pressure drop during the flow of oil and water without gas injection.     

Studies on two-phase co-current air/non-Newtonian shear-thinning fluid flows in inclined smooth pipes

In this work, co-current flow characteristics of air/non-Newtonian liquid systems in inclined smooth pipes are studied experimentally and theoretically using transparent tubes of 20, 40 and 60 mm in diameter. Each tube includes two 10 m long pipe branches connected by a U-bend that is capable of being inclined to any angle, from a completely horizontal to a fully vertical position. The flow rate of each phase is varied over a wide range. The studied flow phenomena are bubbly flow, stratified flow, plug flow, slug flow, churn flow and annular flow. These are observed and recorded by a high-speed camera over a wide range of operating conditions. The effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied. The Heywood–Charles model for horizontal flow was modified to accommodate stratified flow in inclined pipes, taking into account the average void fraction and pressure drop of the mixture flow of a gas/non-Newtonian liquid. The pressure drop gradient model of Taitel and Barnea for a gas/Newtonian liquid slug flow was extended to include liquids possessing shear-thinning flow behaviour in inclined pipes. The comparison of the predicted values with the experimental data shows that the models presented here provide a reasonable estimate of the average void fraction and the corresponding pressure drop for the mixture flow of a gas/non-Newtonian liquid.     

Determination of slug permeability factor for pressure drop prediction of slug flow pneumatic conveying

Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction,which limits their capability for increased predictive accuracy relative to experimental data.This is partly because of the nature of slug flow pneumatic conveying system,which,as a dynamic system,never becomes stable.By utilising conservation of mass (airflow),a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour.The rate of air permeation through slug,one of the important factors in the conservation model,is expressed as a function of a slug permeability factor.Other factors such as slug velocity,slug length and the fraction of stationary layer were also considered.Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model,showing good agreement between the model and experimental results.     

Determination of slug permeability factor for pressure drop prediction of slug flow pneumatic conveying

Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction, which limits their capability for increased predictive accuracy relative to experimental data. This is partly because of the nature of slug flow pneumatic conveying system, which, as a dynamic system, never becomes stable. By utilising conservation of mass （airflow）, a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour. The rate of air permeation through slug, one of the important factors in the conservation model, is expressed as a function of a slug permeability factor. Other factors such as slug velocity, slug length and the fraction of stationary layer were also considered. Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model, showing good agreement between the model and experimental results.     

Effect of diameter on two-phase pressure drop in narrow tubes

The effect of tube diameter on two-phase frictional pressure drop was investigated in circular tubes with inner diameters of 0.6, 1.2, 1.7, 2.6 and 3.4 mm using air and water. The gas and liquid superficial velocity ranges were 0.01-50 m/s and 0.01-3 m/s, respectively. The gas and liquid flow rates were measured and the two-phase flow pattern images were recorded using high-speed CMOS camera. Unique flow patterns were observed for smaller tube diameters. Pressure drop was measured and compared with various existing models such as homogeneous model and Lockhart-Martinelli model. It appears that the dominant effect of surface tension shrinking the flow stratification in the annular regime is important. It was found that existing models are inadequate in predicting the pressure drop for all the flow regimes visualized. Based on the analysis of present experimental frictional pressure drop data a correlation is proposed for predicting Chisholm parameter “C” in slug annular flow pattern. For all other flow regimes Chisholm’s original correlation appears to be adequate except the bubbly flow regime where homogeneous model works well. The modification results in overall mean deviation of pressure drop within 25% for all tube diameters considered. This approach of flow regime based modification of liquid gas interaction parameter appears to be the key to pressure drop prediction in narrow tubes.     

Forced convective flow and heat transfer of upward cocurrent air–water slug flow in vertical plain and swirl tubes

This experimental study comparatively examined the two-phase flow structures, pressured drops and heat transfer performances for the cocurrent air–water slug flows in the vertical tubes with and without the spiky twisted tape insert. The two-phase flow structures in the plain and swirl tubes were imaged using the computerized high frame-rate videography with the Taylor bubble velocity measured. Superficial liquid Reynolds number (Re_L) and air-to-water mass flow ratio (AW), which were respectively in the ranges of 4000–10000 and 0.003–0.02 were selected as the controlling parameters to specify the flow condition and derive the heat transfer correlations. Tube-wise averaged void fraction and Taylor bubble velocity were well correlated by the modified drift flux models for both plain and swirl tubes at the slug flow condition. A set of selected data obtained from the plain and swirl tubes was comparatively examined to highlight the impacts of the spiky twisted tape on the air–water interfacial structure and the pressure drop and heat transfer performances. Empirical heat transfer correlations that permitted the evaluation of individual and interdependent Re_L and AW impacts on heat transfer in the developed flow regions of the plain and swirl tubes at the slug flow condition were derived.     

Numerical modeling and experimental investigation of gas–liquid slug formation in a microchannel T-junction

Gas–liquid two-phase flow in a microfluidic T-junction with nearly square microchannels of 113 μm hydraulic diameter was investigated experimentally and numerically. Air and water superficial velocities were 0.018–0.791 m/s and 0.042–0.757 m/s, respectively. Three-dimensional modeling was performed with computational fluid dynamics (CFD) software FLUENT and the volume of fluid (VOF) model. Slug flow (snapping/breaking/jetting) and stratified flow were observed experimentally. Numerically predicted void fraction followed a linear relationship with the homogeneous void fraction, while experimental values depended on the superficial velocity ratio U_G/U_L. Higher experimental velocity slip caused by gas inlet pressure build-up and oscillation caused deviation from numerical predictions. Velocity slip was found to depend on the cross-sectional area coverage of the gas slug, the formation of a liquid film and the presence of liquid at the channel corners. Numerical modeling was found to require improvement to treat the contact angle and contact line slip, and could benefit from the use of a dynamic boundary condition to simulate the compressible gas phase inlet reservoir.     

Degassing of water-solved gases in thin pipings during fast pressure drops

 A one-dimensional model is presented, which describes the transient two-phase flow in thin pipes during fast pressure drops and degassing by use of Eulerian and Lagrangian systems. The reduction in dimension is obtained by introduction of a geometry model for bubbly and slug flow regimes. The complete model includes the transient two-phase flow, bubble formation and bubble growth. The flow model predicts rising velocities of bubbles and plugs in arbitrary inclined highly accurate pipes. The mass transfer (diffusion) of the dissolved phase is calculated by the bubble growth model. The quality of the model was examined by simulation of experimental series, whereby water was depressurised from the saturation pressure of the dissolved gas mixture (air), by variation of saturation pressure, pressure gradient and pipe geometry. The results of numerical simulation fit the experimental data well. Received on 17 January 2000