双叶片螺旋离心泵固液两相流特性研究

为研究双叶片螺旋离心泵叶轮内固液流动特性,采用Eulerian多相流模型,扩展的标准k-ε湍流方程以及SIMPLE算法,应用流体动力学软件对双叶片螺旋离心泵叶轮内固液两相湍流进行了数值模拟。分析了多粒径及初始固相体积浓度条件下的固相体积浓度分布规律。通过分析可得到固体颗粒存在由叶片压力面向吸力面迁移的趋势,同时有从轮毂侧向轮缘侧运动的趋势;通过外特性分析得到了相同粒径下水泵扬程随固相浓度的升高而减小,相同固相浓度下水泵扬程随粒径的增大而减小的变化趋势。     

搅拌浸出槽固液两相流场的数值模拟

运用Fluent对石煤提钒搅拌浸出槽进行流场模拟,用GAMBIT建立流场实体模型,采用k-ε湍流模型、欧拉一欧拉多相流模型、以及多重参考系法处理搅拌桨区。对搅拌槽在直桨式和旋桨式两种桨型下的流场以及装有挡板或导流筒后的流场情况进行了比较研究,结果表明在同等条件下旋桨式搅拌桨搅拌效果较好,轴向速度比直桨式搅拌桨平均高出120%,在搅拌槽中设置挡板和循环筒有利于改善流场速度分布,从而加强混合效果,但挡板的改善效果更为显著。     

固液两相离心泵内部非定常流动特性研究

为研究固液两相流离心泵内部的非定常流动特性,基于滑移网格方法,采用RNGκ-ε湍流模型以及ASMM代数滑移混合物模型,对一台高比转速固液两相离心泵内部流场进行非定常流动的数值模拟,通过分析清水工况数值计算结果、外特性性能实验结果以及固液两相流非定常数值计算结果,获得了非定常条件下固液两相输送离心泵的瞬时外特性曲线和内部流动及磨损规律。研究结果表明:在一个转动周期内,离心泵的扬程、效率和轴功率均呈现正弦波动特征;动静干涉效应使得叶轮出口处的速度和静压分布均呈现周期性波动;模型泵叶轮前后盖板的磨损情况比蜗壳壁面的磨损严重。上述计算结果可为实现高比转速固液两相流离心泵的优化水力设计和减轻磨损提供一定的理论参考。     

固液两相流泵的研究热点和进展

重点阐述了固液两相流泵的研究现状。从内部的流动规律、泵的性能优化、泵的设计、泵的研究手段四个方面进行了综述。最后提出了4个可行研究方向。     

液固两相流量计的可行性

本文介绍了相关法的测量原理及其实现的可能性;同时,对国外在此方面的概况和发展趋势作了介绍。     

液固两相流中固体的测量

讨论了液固两相流中固体量的计算问题与方法，并讨论了实用的检测仪表选用的问题，简介了部分应用实例。     

深海扬矿泵内固液两相流动模型研究

为选用合理的固液两相流动模型用于深海扬矿泵内矿物浆体的计算。针对深海海底矿物具有颗粒粒级跨度大且粒径大的特点,本文分别选用粗颗粒-均质浆体计算模型和固液两相混合物浆体计算模型,开展扬矿泵数值模拟分析。研究发现,粗颗粒-均质浆体计算模型计算得到的内部流场与固液两相混合物浆体计算模型得到的内部流场是相似的,所以该模型可以用来分析扬矿泵的内部流场;该模型减少了颗粒追踪数量可以节约计算时间;将两种计算方法得到的扬矿泵外特性与试验结果进行比较,发现该模型计算得到的泵扬程与功率均更接近试验结果,说明该模型在扬矿泵性能计算是有优势的。     

离心泵叶轮内部液固两相湍流的数值模拟

为了深入了解离心泵叶轮内液固两相流流态,利用商用软件FLUENT6．2对叶轮内部不可压液固两相流动进行了数值模拟,获得了叶轮内的相对速度分布、压力分布以及固相浓度分布。研究结果表明。由于固体颗粒的存在将对液相相对速度场产生影响,造成泵输送液固两相流时的扬程比输送单相流时有所下降。     

磨粒流加工的固液两相流模型及压力特性模拟

以FLUENT软件为计算平台,采用Spalart-Allmaras固液两相Mixture湍流模型对磨粒流加工过程中磨粒流的流动形态进行了数值模拟,结果表明：增大压力差可提高通道中流体的平均速度,增大边界层与壁面流速差可提高加工效率;通过改变进口压力得到非稳态流场,能够使近壁面处的磨粒数目增多,有利于加工效率的提高。同时,模拟结果还反映了黏度对磨粒流加工有重要影响。数值模拟结果为磨粒流加工过程中的参数选择提供了参考依据。     

Unsteady numerical analysis of the liquid-solid two-phase flow around a step using Eulerian-Lagrangian and the filter-based RANS method

The present study adopts the filter-based RANS (k-ε) method to analyze unsteady liquid-solid two-phase flow around a step in a rectangle channel. Numerical simulation was carried out in three dimensions using Eulerian-Lagrangian approach, in which the continuous phase is treated by Eulerian method and the motions of the dispersed phases are solved by Lagrangian method. The filter-based unsteady RANS (k-ε) model was implemented via user-defined functions in ANSYS Fluent 14.0. The flow field measurement by PIV experiment and the pressure fluctuation downstream the step were carried out for validation. Based on the comparison between the numerical and experimental data, results show that the pressure and velocity distributions were successfully reproduced. Compared with the standard k-ε model, the filter-based model can improve the prediction accuracy for wake flow and particle motion downstream the step. Furthermore, the numerical simulation reveals that the vorticity described by Q-criterion, promotes the particle motion at the wake area. However, the significant discrepancy of the particle distribution in the wake indicates the importance of turbulence modeling method for liquid-solid two-phase flow simulation.

     

基于两相流空穴模型的比例阀流量特性分析

比例阀是大型柴油机柱塞泵核心元件,比例阀的性能关系到液压控制系统的特性.针对比例阀节流口对流量特性影响等问题,采用数值模拟和实验相结合的方法,分析了比例阀不同阀口结构下的流动特性.首先,基于Fluent仿真软件两相流Schnerr-Sau-er空穴模型,分析了3种不同节流口下阀的空穴情况和流量特性;然后,在比例阀性能实...     

Online rheological measurement of dilute liquid-solid two-phase flow with ultrasound Doppler technique

An online and non-invasive ultrasound Doppler based rheometric method is proposed to measure the flow parameters in a dilute liquid-solid two-phase flow and analyze its rheological behaviours. The flow rate is obtained by integrating the ultrasound Doppler velocity profiles through annuluses formed across the cross-sectional area of the pipe while the pressure drop is calculated by choosing suitable models that captures the working conditions of quasi-homogeneous and heterogeneous dilute liquid-solid flows. Wall shear rate and wall shear stress are obtained from the above measurements with the rheological measurement models established. An experimental platform is built to form polystyrene-water and sand-water liquid-solid two-phase fluids for tests. The proposed method has mean absolute errors of 2.53% and 3.49% in flow rate measurement and 3.67% and 5.87% in pressure measurement for polystyrene-water and sand-water fluids, respectively. The experimental results have shown that the rheological characteristics of both fluids fit well with the power law fluid model.     

基于FLUENT数值模拟的离心泵内冰浆两相流流动特性分析

针对冰浆两相流在离心泵的流动特性问题,基于欧拉法建立冰浆Mixture两相流模型,通过FLUENT软件对冰浆流动特性进行数值模拟,得到了在不同流量工况下的离心泵内部压力场、速度场以及冰晶颗粒分布特性.多次数值计算,获得离心泵在输送含冰率为10％的冰浆时的性能特性曲线,并与该离心泵在输送清水时的性能曲线进行了对比分析.研...     

Numerical study on characteristics of turbulent two-phase gas-particle flow using multi-fluid model

The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian method. A computer code is developed for the numerical study by using the k-ɛ-k _p two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is between 10⁻⁵ and 10⁻² for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number (St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number (St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected by the gas phase. A large particle volume fraction (α _p ≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction (α _p ≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and particle velocities.     

基于双流体模型的简易化两相揣拌流场数值模拟

基于双流体模型对混凝土搅拌运输车搅拌筒内搅拌介质进行了简易化的数值模拟,为搅拌筒参数优劣评定提供了有效的参照模型.即将混凝土搅拌运输车搅拌筒中搅拌介质(石子与泥浆)的流固多相处理成密度不同且互相贯穿的介质,以搅拌筒和搅拌叶片为动态边界条件,在流体有限元理论下,实现了基于搅拌筒设计参数变化的简易化多相流场数值模拟.从而在混凝土搅拌运输车搅拌筒数字化设计过程中,在对参数的优劣(减小搅拌介质的离析度和提高搅拌筒的出料速度等)评定时,提供了定量化、可视化的参照模型.     

Flow state monitoring of gas-water two-phase flow using multi-Gaussian mixture model based on canonical variate analysis

As a highly complex and time-varying process, gas-water two-phase flow is commonly encountered in industries. It has a variety of typical flow states and transition flow states. Accurate identification and monitoring of flow states is not only beneficial to further study of two-phase flow but also helpful for stable operation and economic efficiency of process industry. Combining canonical variate analysis (CVA) and Gaussian mixture model (GMM), a strategy called multi-CVA-GMM is proposed for flow state monitoring in gas-water two-phase flow. CVA is used to extract flow state features from the perspective of correlation between historical data and future data, which solves the cross correlation and temporal correlation of multi-sensor measurement data. GMM calculates the possibility that the current flow state belongs to each typical flow pattern and judges the current flow state by probability indicators. It is conducive to follow-up use of Bayesian inference probability and Mahalanobis distance-based (BID) indicator for flow state monitoring, which avoids repeated traversal of multiple CVA-GMM models and improves the efficiency of the monitoring process. The probability indicators can also be used to analyze transition flow states. The method combining the probabilistic idea of GMM with the deterministic idea of multimodal modeling can accurately identify the current flow state and effectively monitor the evolution of flow state. The multi-CVA-GMM method is validated by using the measured data of the horizontal flow loop of gas-water two-phase flow experimental facility, and its effectiveness is proved.     

Coupled model of dual differential pressure (DDP) for two-phase flow measurement based on phase-isolation method

Phase-isolation is a novel ever-increasing multiphase separation technology, which can facilitate the multiphase fluid flowing concurrently with a substantially clear interface between two phases, and the phenomenon is promisingly employed for the separation and measurement of multiphase flows. Phase-isolation can be implemented by different kinds of lateral forces, of which the centrifugal force induced by the swirlers is the most convenient method. The radial pressure drop between pipe wall and pipe center, and the axial pressure drop along the pipe wall occurs at the downstream of the swirler. In the paper, the coupling model of dual differential pressure (DDP) including the radial-axial differential pressure and radial-radial differential pressure was built employing centrifugal phase-isolation for oil-water two-phase flow, and the theoretical measurement models were validated by our experimental data. At certain cross sections downstream of the swirler, the deviations between theoretical and experimental result of the volumetric oil fraction λ_o and mass flowrate Q_m were below ±7.16% and ±1.14% respectively when the radial-axial differential pressure was adopted, while the deviations between theoretical and experimental result of λ_o and Q_m were below ±6.91% and ±1.13% respectively using the radial-radial differential pressure. The acceptable deviation indicates that the DDP model can be the reference for the analysis and application of two-phase flow in the academic research and practical engineering.     

基于二相模型的三相异步电机机械特性的研究

针对基于三相异步电动机物理模型的数学模型分析十分复杂的问题,通过将三相异步电动机数学模型转换到d-q坐标系,利用单相异步电动机的双旋转磁场分析法,并利用二相电机的物理模型和等效电路模型,对三相异步电动机机械特性等进行了研究,推导出了基于二相模型的三相电机的机械特性方程。实验结果证明了该方法的可行性。     

一种基于经验模式分解的气液两相流流型识别方法

提出了一种基于经验模式分解的气液两相流流型识别方法.该方法首先对压差波动信号进行经验模式分解,将其分解为多个平稳的固有模式函数之和,再选取若干个包含主要流型信息的IMF分量,并从中提取时域特征指标-峭度系数作为LVQ神经网络的输入参数,从而实现流型的智能识别.对水平管内空气-水两相流流型的识别结果表明:以EMD为预处理器提取峭度系数的LVQ网络识别方法具有更高的识别率,可以准确、有效地识别流型.