A modified cross-correlation algorithm for PIV image processing of particle-fluid two-phase flow

PIV (Particle Image Velocimetry) technique for flow field measurement has achieved popular self-identify through over ten years development, and its application range is becoming wider and wider. PIV post-processing techniques have a great influence on the success of particle-fluid two-phase flow field measurement and thus become a hot and difficult topic. In the present study, a Phase Respective Identification Algorithm (PRIA) is introduced to separate low-density solid particles or bubbles and high-density tracer particles from the PIV image of particle-fluid two-phase flow. PTV (Particle Tracking Velocimetry) technique is employed to calculate the velocity fields of low-density solid particles or bubbles. For the velocity fields of high-density solid particles or bubble phase and continuous phase traced by high-density smaller particles, based on the thought of wavelet transform and multi-resolution analysis and the theory of cross-correlation of image, a delaminated processing algorithm (MCCWM) is presented to conquer the limitation of conventional Fourier transform. The algorithm is firstly testified on synthetic two-phase flows, such as uniform steady flow, shearing flow and rotating flow, and the computational results from the simulated particle images are in reasonable agreement with the given simulated data. The algorithm is then applied to images of actual bubble-liquid two-phase flow and jet flow, and the results also confirmed that the algorithm proposed in the present study has good performance and reliability for post-processing PIV images of particle-fluid two-phase flow.     

发夹式换热器管束流致振动数值模拟研究

运用计算流体力学方法,采用ANSYS CFX软件对发夹式换热器的壳侧流场进行了三维数值模拟。流场计算中采用多孔介质模型对管束区域进行简化,分析了壳侧流场的速度分布,结果表明:直管段部分的流体湍流强度大于弯管段,且外层管束所在区域为高流速区,受流体冲刷严重。结合流场信息,通过功率谱生成随机激振力,采用ABAQUS软件模拟计算了湍流激振下管束的振动响应,结果显示管束的面外均方根位移远大于面内位移,且弯管部分的振动位移最大。该研究结果可为发夹式换热器的性能分析和优化设计提供参考和依据。     

航空发动机复杂扭曲叶片分步电解加工研究

为实现复杂扭曲叶片在较小间隙下的稳定加工,提出了一种分步式电解加工的工艺方法,建立了复杂扭曲叶片小间隙(0.2 mm)和大间隙下(0.5 mm)扭曲流道的流道模型,采用有限元法进行了流场仿真研究,结果表明增加流道间隙可以解决流道中涡流和流场紊乱的问题。开展了复杂扭曲叶片小间隙连续式加工和分步式加工的试验研究。结果表明,采用小间隙连续式加工,当阴极进给至3.8 mm位置时,在叶片排气边靠近叶根流道扭曲处出现短路打火情况;而采用分步式加工方式能够实现加工的顺利进行。     

The use of bio-diesel based additive as rheology improver and pour point depressant of Nigerian waxy crude

The chemical method has proved to be the most effective mitigating method of wax deposition in petroleum system as it deals with the root cause of wax formation. Most of the commercial chemicals in the industry are very expensive and toxic. This paper aims the use of biodiesel based additives for improving the rheological behavior and pour points of waxy crude from Nigeria field. The biodiesels derived additives gave better performance than the commercial chemical and the seed oils as greatly improvement in rheology and pour point values of the waxy crude were observed     

托盘式湿法烟气脱硫塔阻力特性研究

采用冷态物理模型结合商用CFD(Computational Fluid Dynamics)软件,对山东某火电厂300 MW机组配套托盘塔的流场和阻力特性进行了研究,取得了孔板阻力损失与液气比之间的二次函数关系。研究结果表明,塔内两相流场分布合理,入口处液滴受烟气的拖拽作用形成明显的干湿界面,负荷和液气比是影响脱硫塔阻力的重要因素。当液气比一定时,托盘上方能够维持相对稳定的持液层及鼓泡过程;满负荷运行时,脱硫塔阻力损失约为1600 Pa,其中孔板占1/4,持液层占3/4。拟合获得了托盘区阻力损失同液气比之间的关系,为托盘塔的应用、运行及优化提供了理论指导。     

面向流屑角突变建模的切削状态参数经验公式的获得及应用

从提高流屑角突变模型的预测精度出发,建立了切削状态参数与3个切削控制参数之间关系的新经验公式。提出了一种通过迭代法准确设定有限元仿真软件刀-屑摩擦因数的方法,并通过直角切削Al6061-T6工件的有限元仿真试验,获得了一组不同切削控制参数组合条件下的切削状态参数数据。根据该数据拟合出剪切角φ、刀-屑摩擦角β、剪切应力τs关于刀具前角γ0、进给量f和切削速度v的经验公式,并通过一组直角切削试验,验证了所得经验公式的有效性。将新建经验公式应用于流屑角突变建模过程后,所得模型关于突变临界切削宽度的平均预测误差减小了27.2%。     

Flow pattern identification and measurement techniques in gas-liquid-liquid three-phase flow: A review

The simultaneous flow of gas, oil, and water forms various flow patterns due to the complex interfacial relationships. Three-phase flow patterns are classified as the gas-liquid and liquid-liquid flow patterns. Pressure drop, void fraction, liquid holdup, and phase distribution are important characteristics of the three-phase flow. These characteristics are generally associated with the three-phase flow patterns. Hence, the knowledge about flow patterns can help to predict the overall behavior of the three-phase flow. Studies have been conducted to identify three-phase flow pattern and their characteristics at various superficial velocities of gas, oil, and water. The major purpose of the studies is to gather information about the three-phase co-current flow and use it for improvement of the efficiency of the flow systems. Therefore, the accuracy of the measurement technique is critical. Several types of flow pattern identification and measurement techniques have been developed to improve accuracy and provide high-quality results. In this article, classical and advanced techniques used for the three-phase flow identification and measurement have been reviewed. The survey will help the researchers working in the area of multiphase flow to choose the right technique based on the objectives of the studies.     

An improved method to visualize two regions of interest synchronously in microfluidics

Multiphase flow in mini/micro channels has been widely studied for its potential in many industrial applications. The normal experimental method cannot capture two separate regions of interest (ROI) with a long distance synchronously for the limited field of views. In order to solve this problem, an improved experimental method is proposed and validated with experimental results. Prism groups are applied to reflect the two regions of interest to a very small shooting zone. Though the actual distance between the two regions is far, the reflected regions adjoin with each other on the top surface of the prisms. Thus, the two regions can be captured synchronously with one image using a small field of view. Two types of configurations with 4 prisms and 6 prisms are compared using gas-liquid and liquid-liquid experimental results. The resolution of the two configurations is similar, while the maximum amplification ratio is smaller for the latter configuration with 6 prisms. The first type is more suitable for experimental studies focusing on the formation and breakup of dispersed phases near two branches. The second configuration is recommended for cases focusing on the formation and fully developed hydraulic characteristics of the dispersed phase. The proposed method is very efficient for studies of hydraulic, heat and mass transfer characteristics of multiphase flows in mini/micro channels.     

潮流能水平轴水轮机在剪切来流下的水动力分析

采用基于计算流体力学方法的全尺度数值模拟计算,建立了适用于潮流能水轮机模拟的剪切来流环境,通过数值计算结果,对潮流能水轮机随时间变化的宏观力和流场特征进行了系统分析,探索水轮机在复杂工况下的水动力特性规律。结果表明,水轮机整个叶轮的总体平均受力在剪切流工况中未受到明显影响; 单个叶片的瞬态轴向力系数和瞬态轴向扭矩系数在旋转周期内出现了明显的周期性变化,且周期性变化幅值随转速增大而增大; 非定常的瞬时轴向扭矩和力的周期性振荡容易引起单个叶片的结构性振动,可能对水轮机的机械结构造成影响。