混凝土泵送中管壁磨损过程的离散元模拟研究

建立了混凝土离散元模型,并通过L箱流动实验校核了该模型,得到了计算参数。采用该模型及得到的参数对混凝土泵送过程进行数值模拟,其中,以颗粒对管壁的冲击力和平均力表征壁面磨损程度,对泵送过程中管壁磨损过程进行研究。分析了泵送速度、弯管角度等因素对管壁磨损分布的影响,预测了最易磨损位置。结果表明：弯管管壁磨损随着泵送速度的增大而增大,随着弯管角度的增大而增大,模拟结果与实际泵送过程中观测到的最易磨损位置吻合较好。     

考虑载荷模拟作用的高压弯头冲蚀数值仿真

在水力压裂过程中,地面高压管汇在管内复杂固液两相流冲击和管体恶劣载荷的耦合作用下,弯头、三通及接头等薄弱部件长期遭受严重的冲蚀磨损,极易导致管件发生断裂破坏,对现场人员及设备构成严重威胁。开展载荷作用下的高压管汇典型材料冲蚀磨损试验,根据试验结果,基于E/CRC冲蚀模型构建一种考虑应力状态影响的新型冲蚀数学模型,所构建的新模型与冲蚀试验数据之间的准确度可达95%以上。采用计算流体力学离散相模型（CFD-DPM）,开展高压管汇件冲蚀性能的三维数值模拟,考察高压弯头在不同压裂工况下的冲蚀磨损程度及空间分布情况。结果表明：在固液两相流冲击下,主要冲蚀区位于靠近弯头出口处的弯头外侧,且管件的最大冲蚀率也位于该处;在弯头内侧二次流涡流的影响下,部分颗粒在流经弯头后会在下游直管内侧积聚,从而在这个区域造成次要冲蚀区;随着流动颗粒斯托克斯系数增加,主要冲蚀区面积增大,次要冲蚀区面积减小;此外,在嵌入新型冲蚀数学模型后,可观察到随着操作压力增大,高压管汇弯头部位的冲蚀磨损率明显增加。     

结构参数对压裂双弯头冲蚀及流致变形的影响*

双弯头管汇是水力压裂地面高压管汇系统中的关键部件,由于高压大排量携砂压裂液在其中多次强制转向,双弯头管汇长期遭受着严重的冲蚀磨损和流致变形。为改善管件冲蚀磨损状态,从管汇结构参数的角度研究其对冲蚀率的影响。采用计算流体力学(CFD)数值模拟,结合离散相模型(DPM)和流固耦合(FSI)方法,对双弯头结构管汇在工况条件下的流致冲蚀和变形情况进行综合分析,研究双弯头结构参数,如连接直管长度、管道内径及弯头间连接角度对冲蚀和变形的影响。结果表明:随着连接直管长度增加,冲蚀率先减小后变化不大,而结构变形程度逐渐增大,综合考虑冲蚀磨损和结构变形,双弯头之间的连接直管长度宜设计为管道外径的4倍;大口径管道的冲蚀磨损程度更低,但会带来更大的变形,因此双弯头管汇的管内径不宜过大或过小;当2个弯头间的连接角度为0°时,冲蚀和变形程度达到最小。     

Numerical simulation on the erosion wear of a multiphase flow pipeline

The devices in coal chemical industries operate with harsh conditions, involving the high temperature, high pressure, and high concentration of pulverized coal particles. Therefore, leakages or perforations of pipelines occur frequently. In this paper, the numerical prediction on the erosion wear of a coal slurry transmission pipeline was conducted. The dense discrete phase model-kinetic theory of granular flow (DDPM-KTGF) and a modified erosion model were adopted to calculate the particle trajectories and erosion rates. In the numerical calculation, the erosion rate curve of 1Cr9Mo steel obtained in the experiments is incorporated into the erosion model. The results showed that the regions with high erosion risks predicted by the modified erosion model were in agreement with the experimental results. Then, the calculation method is validated. It is also found that the particle movements involve partial agglomeration under the drag of centrifugal force and the secondary flow, when they pass through the elbow. Larger particles are prone to impact on the back of the bend, which has more pronounced effect on the erosion wear. The positions of the maximum erosion rate on all the elbows were discussed, which provides a reference for the inspection on the wall thickness of pipeline.     

空间Z形管路液-固两相流冲蚀特性分析

空间Z形管路是油气开采过程典型的结构形式,在工程作业中受到高压高速液-固两相流的作用,容易导致管路系统产生冲蚀磨损失效。基于液-固两相流冲蚀磨损理论,选取合适的冲蚀磨损理论模型,讨论了流速、颗粒直径、质量流量、黏度以及重力等不同流体参数对管路系统弯头处的冲蚀磨损情况。结果表明:管路弯头处的冲蚀区域受内流场的影响存在明显差异,出口端弯头处的最大冲蚀率大于进口端弯管端。流速、颗粒直径、质量流量与整体管路最大冲蚀率呈正相关关系,黏度与整体管路最大冲蚀率呈负相关关系。分析了不同工况下空间Z形管路的冲蚀特性,获得了流体参数对管路冲蚀的影响规律,为工程实际复杂管路系统冲蚀磨损寿命预测提供技术参考。     

Wear modeling and the third body concept

Many laws already exist for wear, but few are really predictive. In order to better understand the wear process, classical wear models are compared to the third body concept. This concept emphasizes that particle detachment mechanisms, the flow of these particles inside the contact, and their ejection from the contact have to be considered in order to describe wear effectively. An analytical demonstration is proposed, that considers the particle detachment process and the particle ejection process separately. These two processes are then linked by a mass equilibrium equation. In continuous sliding, a steady-state wear process can be identified in which the mass of third body particles in the contact remains constant. The source flow and the wear flow (representing, respectively, particle detachment and particle ejection) become equal and constant in time. Initially presented via numerical investigations, this analytical model is then confirmed by simple experiments.     

煤液化多相流输送弯管冲蚀磨损数值研究

针对煤液化中液-固两相流输送过程造成管道系统的冲蚀磨损失效问题,以90°圆形截面弯管结构为研究对象,采用标准k-ε湍流模型、颗粒轨道模型和冲蚀磨损模型,对弯管内的流动特性和壁面磨损率进行数值计算。研究表明,靠近弯管背部的流场速度高于腹部,粒子向背部聚集,导致背部的冲蚀磨损较其它部位更为严重。因此,实际管道系统中的弯管背部应为定点测厚重点监测区域。     

基于CFD数值模拟的异面三通管冲蚀磨损规律研究*

针对管道在输送过程中,由流体中固态颗粒产生的冲蚀磨损导致的失效问题,通过CFD-DPM模型开展关于不同流速、颗粒直径、含砂体积比和异面管夹角对异面三通冲蚀磨损性能影响的分析。结果表明：三管交汇处的弯面是管道主要发生冲蚀磨损的位置,水平两管弯头上侧管壁处是受损最为严重的部位;在流速2~10 m/s、含砂体积比1%~9%、异面管夹角90°~150°、颗粒直径0.1~0.5 mm时,管道的最大冲蚀率随着流速增大呈指数型增长,冲蚀面积明显扩张;低流速下,含砂体积比对最大冲蚀率影响较弱,高流速下,最大冲蚀率与含砂体积比呈线性正相关;异面管夹角的增大降低了管道对固体颗粒的流动约束性,其冲蚀率呈线性减小;最大冲蚀率随颗粒直径的增大整体呈现平缓上升的趋势,大颗粒产生的冲蚀破坏相比小颗粒更为集中一些。     

Characterization of swirling-flow behavior in complex pipeline using bubble trajectory method with stereo particle tracking/image velocimetry

To understand the swirling-flow behavior in a complex pipeline geometry comprising an elbow and orifice, a quantitative flow visualization technique is introduced into the flow-field observation using a bubble trajectory method combined with stereo particle tracking/image velocimetry. For the chosen bubble sizes of approximately 2 mm un a pipe of 56 mm in diameter, their motion is correlated with the mean swirling flow, and when analyzed in a straight swirling flow, the bubbles cluster close to the point of maximum axial velocity for swirl intensities larger than 0.3. Subsequently, this experimental technique is applied to the characterization of a swirling flow in the Mihama pipeline model, for which the streamwise variation of the location of the maximum axial velocity and its magnitude are measured over the full range of the pipeline model. A spiral swirling flow is observed downstream of the elbow owing to the combined effect of the swirling and secondary flows in the elbow. The spiral swirling flow persists in the following straight pipe down to the orifice, where a highly accelerated flow with a high turbulence is generated towards the top wall of the pipe. This result agrees closely with the observation of pipe-wall thinning in the prototype Mihama pipeline.     

Upstream swirl-induction for reduction of erosion damage from slurries in pipeline bends

Industries which transport slurries and other particle-laden liquids in pipes expend the equivalent of millions of pounds every year to repair erosion damage caused by solid particle impingement. It is against this background that the perceived relationship between pipeline erosion and imposed swirling flow fields in pipe bends is important. Definitions of flow fields and particle dispersions which minimise erosive wear are sought to facilitate the development of new designs and geometries for slurry handling equipment. Such an approach is pertinent to industries handling valuable or hazardous material in the face of increasing safety, efficiency and economic requirements. Robust erosive wear models must be developed to explore the advantages of swirl flow and subsequent particle dispersion.

Collaboration between the universities of Nottingham and Southampton is aimed at the reduction of wear at critical locations in slurry handling pipelines by applying swirl-inducing pipes upstream of pipe bends. This paper details the improved particle distributions, particle impingement conditions and lower flowrates resulting from such swirl flow. These factors are discussed in terms of current erosion models and the predicted reduction in wear rates. Parallel visualisation studies using simulant particle-laden liquids augment computational modelling of the flow patterns.     

基于流体动力学的弯管应力有限元分析

由直管弯制而成的弯管几何形状和结构复杂,在流体作用下受力复杂,准确的应力分析是进行强度计算和弯管设计的重要前提。使用ANSYS流体-固体有限元分析软件,建立了管内流体动力学分析和弯管结构应力三维分析模型,利用两种不同物理环境的转换,得出了弯管在流体不均匀压力作用下的应力分布,讨论了流量、弯管加工缺陷对弯管应力的影响。     

Fluid dynamic mechanisms of particle flow causing ductile and brittle erosion

Traditional prediction of erosion focuses on the use of velocity and impact angle of particles as independent variables in analytically derived models. This approach is most suitable for numerical predictions of erosion in disperse flow fields where particle trajectories may easily be followed prior to impact. For dense particle flows, the prediction of individual particle or particle cluster movement is nearly never attempted by following trajectories. Instead, two-fluid Eulerian–Eulerian approaches are used in which a continuous particle fluid phase is considered.The present study shows that the impact velocity and angle of attack of particles at the eroding surface are difficult to obtain for dense flows, thus being difficult to consider as parameters for predicting erosion. Instead, it is proposed that the normal and the shearing components of the viscous dissipation of the particulate phase are more suitable as independent flow variables governing the erosion process. These variables describe deformation and cutting wear processes, respectively, and are readily derived from the flow field.Eulerian erosion models are proposed, based on these independent variables. It is possible to implement previous results and theories concerning the material–mechanical interaction between the abrasive and an eroding surface to achieve model improvements. In this work, only a simple model taking into account a threshold elastic strain limit is proposed, to more correctly model the deformation wear.The particle-flow boundary condition — a partial-slip condition — significantly influences the erosion process, particularly the cutting erosion. The boundary condition depends on parameters such as the local particle phase flow, the mean diameter and the sharpness of the abrasive as well as the surface roughness.A simple 2D test application — a jet stream of particles impinging a tilted plate — is presented, and the qualitative angular behaviour of ductile and brittle erosion is reproduced at the target position. A scheme is presented for determination of material constants and suitable boundary conditions to be used in the proposed erosion models.     

Modelling third body flows with a discrete element method—a tool for understanding wear with adhesive particles

This work presents a fundamental approach to the study of the wear process by considering the detachment of particles, their flow in the contact and their ejection. A numerical model is constructed in order to visualize and to accurately measure these phenomena. Moreover, the adhesion between the detached particles and with the rubbing surfaces can be simulated and controlled. This physicochemical parameter plays an antagonistic role on the wear process. The greater the particle adhesion the thicker the interfacial layer will be, though with a corresponding reduction in the ejection of particles. Finally, emphasis is placed on the influence of the interfacial layer on the wear process.     

基于Fluent的煤粉燃烧器风管流场数值模拟与分析

利用Fluent软件对煤风管道内气-固两相流进行模拟仿真,通过观察固体颗粒运动轨迹,对管道内冲蚀磨损进行研究分析。利用RNG k-ε湍流模型和拉格朗日离散相模型对燃烧器煤风管道内煤粉颗粒-空气两相流场进行耦合数值模拟,对比分析了输煤管在不同角度α时的流场特性和颗粒运动轨迹,发现当α≤15°时,管道壁面冲蚀磨损率有所降低;管道中除了存在冲蚀磨损,同时还伴随有摩擦磨损。通过对计算结果的分析和讨论,发现燃烧器设计的不合理因素,对煤粉燃烧器结构改进和相关参数优化有一定指导意义。     

A model and the methodology for determining wear particle generation rate and filter efficiency in a diesel engine using ferrography

A mathematical model was developed that describes the wear particle concentration as a function of time in a diesel engine. This model contains engine and lubrication system parameters that determine the concentration of wear particles in the engine sump. These variables are the oil system volume, oil flow rate, particle generation rate, filtering efficiency and the initial particle concentration. The model was employed to study the wear particle concentrations in the sump and the mass of particles in the filter for the Cummins VT-903 diesel engine. In addition, the model was used to develop a testing methodology for determining wear particle generation rates and filter efficiencies from used oil analysis. This testing methodology uses ferrography together with computer programs to yield accurate statistical information on the data as curve fitted to the model. The test set-up incorporated a remote-controlled sampling system that enabled the accurate and periodic taking of oil samples over an engine test approximately 5 h in duration.

Results of this research indicate that equilibrium wear particle concentrations increase with an increase in engine speed and load. The wear particle generation rate and filter efficiency as determined by the test methodology were found to decrease with an increase in engine speed and load. After oil and filter changes, the wear particle generation rate and filter efficiency continually increased with cumulative engine time up to approximately 11 h. The test methods used to obtain the results above were found to be repeatable to within ±15% and could conceivably be employed to determine wear parameters on other diesel engines as well as the effects that other engine variables such as lubricants, oil temperature, coolant temperature and engine components have on the wear parameters.     

旋流气力输运中水平管道管壁磨损的流体力学仿真与分析

旋流气力输运,在一定程度上很好的解决了固体颗粒在水平管道运输管道中堆积堵塞的问题。但是固体颗粒在管道中贴壁旋转,由于离心力和惯性力的作用会造成管壁的严重磨损,其磨损率与管壁材料、固体颗粒旋转强度等众多因素有关。文中基于水平管道旋流气力输运过程进行CFX仿真分析,通过采用雷诺应力模型对系统中旋流强度进行对比分析,并结合对磨损形成机理的探讨,研究了旋流气力输运系统中管道壁面磨损的情况,并探讨了改善管壁磨损的一些措施。     

Modeling of electromagnetic separation of inclusions from molten metals

The presence of inclusions greatly influences the mechanical and the corrosion resistance of metallic alloys. These influential effects become more crucial when using metallic scrap, due to the high levels of inclusions and other contaminants such as non-metallic and oxides particles. Metal cleanliness requirements are becoming more striking, enforcing higher demands on the efficiency and flexibility of refining methods. Recently electromagnetic separation technique has been considered as a new method for the production of metals free from inclusions. In this study, a mathematical model has been developed to simulate the flow of molten metal through a channel in the presence of electromagnetic force field generated by interaction between a stationary electromagnetic field and DC current passing through the melt. A generalized model based on Newton's second law of motion was developed for the motion of inclusions in the melt flowing through the channel of separator by considering different forces acting on particle including electromagnetic force. A physical model was designed and constructed to visualize the inclusion separation phenomena and to verify the mathematical model. The predicted particle trajectories and separation in the physical model were compared with those obtained from experiments which showed reasonably good agreement. Parametric studies were performed using the mathematical model to evaluate the effects of various parameters, such as electromagnetic force strength, particle size and melt inlet velocity on the inclusion removal efficiency.     

弯管冲蚀失效流固耦合机理及数值模拟

针对流体输送管道失效研究中存在的问题,主要研究腐蚀与流体流动的交互作用对管道冲蚀破坏的作用机理。建立流固耦合数理模型,推导出在任意拉格朗日-欧拉(Arbitrary Lagrange-Euler, ALE)描述下的粘性流体N-S方程和腐蚀产物保护膜固体区域的控制方程,分析管壁边界层多相流介质流动与腐蚀产物保护膜破损之间的耦合作用。以弯管的冲蚀失效为例,结合弯管的结构特性、多相流的物性参数,运用ANSYS有限元分析软件,采用物理环境顺序耦合法进行流固耦合数值模拟,分析管壁腐蚀产物保护膜的变形程度和受力状态,判定弯管冲蚀破坏的危险区域和失效趋势;现场测厚数据与仿真计算结果基本吻合,验证仿真计算的可靠性和可行性,该方法可用于管道输送系统的风险预测、安全评估和工艺改造。     

Accelerated High Speed Water Erosion Test for Concrete Wear Debris Analysis

This paper contains investigations of wear particles generated during the erosive wear of four different concrete, mixtures by high velocity water flow at velocities of about 700 m/s.ⁱ The wear particles were collected, dried and analyzed by sieve experiments. Based on the sieve analysis, specific surface and average grain diameter of the particle samples were estimated. 'Using simple, comminution relations, the specific crack length of every' sample is calculated. It is shown that all estimated parameters exhibit a strong relationship to characteristic material properties, such as compressive strength, Young's modulus, and absorbed fracture energy. It was found by regression analysis that the average debris wear size can be effectively characterized by the absorbed fracture energy of the concrete sample. It is concluded that these relations are the result of different paths of fracture propagation through the materials during the generation of a microcrack network.     

磨粒在磨粒探测器中的沉降运动研究

研究了在线铁谱仪磨粒探测器中的磨粒沉降运动规律,建立了磨粒在流道-磁极倾角方案下的运动模型,采用有限元法仿真了直流电磁装置的磁场分布情况,并研究了初始高度y0和磨粒直径D等参数对磨粒沉积位置的影响。结果表明,在油样流动方向和磁极之间存在倾角γ的条件下,磨粒在磨粒探测器中按照尺寸大小有序沉积,且沉积位置和油样入口端之间的距离随着初始高度y0增加而增加。