固-液两相流黑水管道冲蚀磨损的数值模拟研究

煤气化黑水处理系统管道由于其流体介质高含固体颗粒和腐蚀性介质，且工作在高温、高压差环境中，极易受到冲蚀磨损和腐蚀的耦合作用而失效，影响其服役寿命. 采用计算流体力学(CFD)方法数值模拟研究了煤气化黑水处理系统固-液两相流管道的冲蚀磨损行为和机理，以及流体介质速度和固体颗粒粒径对管道冲蚀磨损的影响规律，并分析了盲通管和涡室结构对弯管冲蚀磨损行为的优化改善效果. 研究结果显示，煤气化黑水处理系统管线的冲蚀高危区主要分布在弯管外拱和变径管等结构突变区域；管道冲蚀磨损行为与其内部流体的运动和颗粒冲击特性有关；管道的冲蚀率均随着流体速度的增加而加剧，而粒径对弯管和变径管冲蚀率的影响并非单调关系，这与颗粒受力作用有关；弯管优化分析显示，涡室结构可以降低弯管的最大冲蚀率，减缓弯管的冲蚀磨损.      

冲蚀磨损与冲蚀、空蚀交互磨损的对比研究

基于计算流体力学(computational fluid dynamics,CFD)方法,数值对比研究了在模拟水轮机工况中不同转速时,冲蚀与冲蚀、空蚀交互作用时,转盘表面的流场(压力场、流体浓度分布),然后在转盘式磨损装置上,进行了汽液固三相冲蚀与空蚀交互磨损试验.结果表明:对于冲蚀磨损来说,随着转速增加,压力增大,在冲蚀作用下加入空蚀磨损,压力增高,磨损加剧;而对于交互磨损来说,随着转速增加,转盘表面的空蚀磨损区域从空化孔附近开始沿着转盘旋转的反方向偏移,并且磨损程度加剧;数值计算的气泡较多且压力梯度较高区域和试验转盘磨损区域基本一致,数值计算结果和试验结果吻合得较好.     

SiC/环氧树脂复合材料冲蚀磨损性能的研究

采用环氧树脂为粘接剂制备了SiC/环氧树脂复合材料,在自制的射流式冲蚀磨损试验机上研究了SiC/环氧树脂的冲蚀磨损性能.结果表明:大尺寸SiC颗粒制备的复合材料较小尺寸SiC颗粒制备的复合材料具有更好的冲蚀磨损性能,且大尺寸SiC颗粒复合材料的冲蚀磨损性能优于Q235钢,而小尺寸SiC颗粒复合材料则低于Q235钢.随着冲蚀角度的变化,其平行材料表面的切削分量和垂直材料表面的冲击分量将会发生变化,低角度冲蚀磨损机理以显微切削和碾压造成环氧树脂及SiC颗粒的层片状脱落为主转变为高角度冲蚀磨损以SiC颗粒碎裂造成环氧树脂疲劳脱落为主.     

液固两相流冲洗油管道的冲蚀磨损特性数值模拟及分析

以液固两相流冲洗油管道为研究对象,采用Realizableκ-ε湍流模型、随机轨道模型,结合液固两相流冲蚀磨损试验,建立修正的冲蚀磨损数理模型,数值预测典型工况下冲洗油管道内速度、压力、冲蚀磨损率等流动参数分布情况,分析了冲蚀磨损的形成机制.研究结果表明:受曲率半径影响,冲洗油管道冲蚀磨损速率随曲率半径的增加而减小;由于颗粒惯性及管内二次流影响,弯头中间区域外侧壁面和出口直管段内侧面磨损较为严重,三通管件的最大冲蚀磨损率位于孔口处,数值预测结果与失效解剖案例吻合.本文建立的冲蚀磨损定量预测方法,适用于压力管道的风险评定及寿命预测.     

几种水机常用金属材料的冲蚀磨损性能研究

研究了在水力机械中普遍应用的铸铁(HT200)、中碳结构铸钢(40#)、不锈钢(1Cr18Ni9Ti)和高铬铸铁(KmTBCr26)4种材料的冲蚀磨损规律,得出了材料的冲蚀磨损率随磨损时间、冲蚀速度、磨粒浓度和粒径变化的规律,同时根据观察材料冲蚀磨损表面形貌探讨了其冲蚀磨损机理.结果表明:材料的冲蚀磨损性能受到材料基本机械性能的控制,其中高硬度材料的抗冲蚀性能较好,在相同试验条件下其磨损率由大到小排列顺序为HT200＞40#＞1Cr18Ni9Ti＞KmTBCr26;4种材料的冲蚀磨损率随磨粒粒径、浆料浓度和磨粒冲击速度的变化规律基本一致,当磨粒粒径小于425 μm时,磨粒粒径对KmTBCr26和1Cr18Ni9Ti的磨损率影响很小;金属材料的组织结构对材料的冲蚀磨损性能和机理影响较大,其中KmTBCr26和1Cr18Ni9Ti的冲蚀磨损机理以脆性断裂、破裂及颗粒脱落为主,而HT200和40#的冲蚀磨损机理以选择性切削式冲蚀磨损为主.     

一种减轻固粒对壁面冲蚀磨损的新方法

针对带固粒的近壁流场，提出了在壁面上开凿纵向浅沟槽以减轻固粒对壁面冲蚀磨损的方法．采用改进的κ-ε湍流模式和气-固两相双向耦合模型，计算了流场中颗粒的速度、轨迹以及固粒对壁面的冲蚀磨损，并进行了相应的试验对比．结果表明：在壁面上开凿纵向沟槽能减轻固粒对壁面的磨损；在一定的沟槽高度下，当沟槽宽度同沟槽问距离相等时，减轻磨损的效果最明显；在一定颗粒尺寸范围内，大颗粒导致磨损质量损失增大，当颗粒尺寸超过某一临界值后，颗粒尺寸对磨损的影响较小．进口处颗粒运动方向对壁面磨损具有直接影响．     

DH32船用钢板在模拟极地破冰环境中的冰载荷冲蚀磨损性能研究

使用自行设计并加工的低温海冰冲蚀磨损试验机研究了船用低温钢板DH32在模拟极地破冰环境下不同船速条件下的耐海冰冲蚀磨损性能. 利用失重法研究了不同转速下的冲蚀磨损失重率,通过扫描电子显微镜和白光干涉显微镜对材料冲蚀磨损后的微观组织形貌和表面3D形貌轮廓进行观察,并讨论了不同冰水比的冰载荷冲蚀磨损-腐蚀机理. 结果表明:随着模拟船速的不断增加,DH32钢的冲蚀磨损失重率也随之增大. 当转速为3.3 m/s(模拟船速6节)、冰水比为1∶2时,DH32钢样的冲蚀磨损失重率升高幅度最大,达到12%,其在海冰条件下冲蚀磨损以冲蚀磨损坑、犁削、犁沟以及滑坑等失效机理为主. 另外,文中还讨论了常温下砂粒冲蚀磨损和不同冰水比的冰载荷冲蚀磨损的对照性,为后续制定与海冰载荷相关的材料冲蚀磨损标准提供数据支持. 试验证实,以5.5 m/s在43%(质量分数)石英砂+海水溶液中进行冲蚀磨损试验可以近似模拟2∶1冰水比条件下海冰冲蚀磨损对材料破坏作用.      

钢结构表面涂层受风沙冲蚀机理和评价方法

内蒙古中西部地区钢结构表面涂层受风沙冲蚀磨损严重.在模拟钢结构涂层受风沙冲蚀磨损试验的基础上,应用扫描电子显微镜(SEM)观测涂层在不同冲蚀条件下的冲蚀磨损部位微观形貌,分析涂层材料受风沙冲蚀磨损的损伤机理,提出了评价涂层冲蚀磨损程度的计算方法.结果表明:低角度冲蚀时微切削作用占主导,硬度起决定作用,高角度冲蚀时挤压变形占主导,柔韧性起决定作用,由于涂层硬度较低,柔韧性好,所以高角度时涂层的耐冲蚀性能较好;最大冲蚀磨损失重量出现在45°左右,是由于该材料具有介于塑性和脆性材料之间的冲蚀磨损特性;速度越大,粒子的动能越大,冲蚀磨损失重量越大;在低浓度时,冲蚀磨损失重量随着浓度的增加而增加,而在高浓度时则出现下降的趋势;评价公式的计算结果与实验结果吻合.研究结果为钢结构涂层的耐久性研究提供了理论依据.     

秦岭公路隧道2号竖井地应力与岩爆分析

利用水平圆柱形激波管对激波驱动的可压缩性气固两相流进行了试验研究. 利用压电式压力传感器、电荷放大器、示波器及计算机组成的压力信号测试系统, 对激波 与颗粒作用前后的气相参数进行测量及分析. 试验中测得了激波在管中的传播速 度, 波后气流的压力, 反射激波、透射激波的压力和速度等. 分别考察颗粒、装载 比、驱动气源以及入射激波马赫数等因素的差异对气相参数的影响. 试验结果表明: 激波与颗粒群相互作用时, 会产生反射激波和透射激波, 其强度与驱动气源、颗粒大小、颗粒装载比等参数有关; 激波衰减率随着装载比、马赫数的增大而减小. 研究指出, 在颗粒群被激波加速的初始阶段, 颗粒间的弹性碰撞起着重要的作用.     

激波驱动的气固两相流的动态压力测量

利用水平圆柱形激波管对激波驱动的可压缩性气固两相流进行了试验研究.利用压电式压力传感器、电荷放大器、示波器及计算机组成的压力信号测试系统, 对激波与颗粒作用前后的气相参数进行测量及分析. 试验中测得了激波在管中的传播速度, 波后气流的压力, 反射激波、透射激波的压力和速度等. 分别考察颗粒、装载比、驱动气源以及入射激波马赫数等因素的差异对气相参数的影响.试验结果表明: 激波与颗粒群相互作用时, 会产生反射激波和透射激波,其强度与驱动气源、颗粒大小、颗粒装载比等参数有关;激波衰减率随着装载比、马赫数的增大而减小. 研究指出,在颗粒群被激波加速的初始阶段, 颗粒间的弹性碰撞起着重要的作用.      

First observations on break-up of particle agglomerates in shock waves

The destruction of solid agglomerates suspended in argon by means of shock waves (1 <M _s < 5) has been studied experimentally using a conventional shock tube apparatus. The change in particle size was measured by time-dependent in situ laser light scattering of the particle ensemble in the shock wave. The test facilities used are given in details, and the principle of the Mie-theory, necessary for complete understanding of the data reduction, is described. In this paper data reduction and first analysis employing two independent trial solutions involving the Mie-theory for polydisperse, spherical particle-ensembles are presented. Three types of agglomerates suspended in argon with a mean initial size of about 1 gm were exposed to the shock wave and different size reduction behaviours were observed. The deagglomeration effect depends largely on the wave intensity and on the physico-chemical structure of the particle aggregates.     

On the energy conservation and critical velocities for the propagation of a ＂steady-shock＂ wave in a bar made of cellular material

The propagation of shock waves in a cellular bar is systematically studied in the framework of continuum solids by adopting two idealized material models, viz. the dynamic rigid, perfectly plastic, locking （D-R-PP-L） model and the dynamic rigid, linear hardening plastic, locking （D-R-LHP-L） model, both considering the effects of strain-rate on the material properties. The shock wave speed relevant to these two models is derived. Consider the case of a bar made of one of such material with initial length L 0 and initial velocity v i impinging onto a rigid target. The variations of the stress, strain, particle velocity, specific internal energy across the shock wave and the cease distance of shock wave are all determined analytically. In particular the ＂energy conservation condition＂ and the ＂kinematic existence condition＂ as proposed by Tan et al. （2005） is re-examined, showing that the ＂energy conservation condition＂ and the consequent ＂critical velocity＂, i.e. the shock can only be generated and sustained in R-PP-L bars when the impact velocity is above this critical velocity, is incorrect. Instead, with elastic deformation, strain-hardening and strain-rate sensitivity of the cellular materials being considered, it is appropriate to redefine a first and a second critical impact velocity for the existence and propagation of shock waves in cellular solids. Starting from the basic relations for shock wave propagating in D-R-LHP-L cellular materials, a new method for inversely determining the dynamic stress-strain curve for cellular materials is proposed. By using e.g. a combination of Taylor bar and Hopkinson pressure bar impact experimental technique, the dynamic stress-strain curve of aluminum foam could bedetermined. Finally, it is demonstrated that this new formulation of shock theory in this one-dimensional stress state can be generalized to shocks in a one-dimensional strain state, i.e. for the case of plate impact on cellular materials, by simply making proper replacements of the elastic and plastic constants.     

冷激波灭火系统中激波对灭火效果和周边环境的影响

为了评估冷激波灭火弹爆炸后形成的激波对灭火效果和周边环境的影响,建立了一套纹影实验装置。通过纹影实验,观察了小尺寸下不同灭火介质爆炸抛撒后激波的形成和传播,并推算了冷激波灭火弹爆炸后油盆边缘附近的波后质点速度。观察发现,水基灭火介质爆炸抛撒后没有形成激波;而粉基灭火介质尽管爆炸抛撒后形成激波,但在油盆边缘附近激波强度较弱,波后质点速度小。与介质抛撒引起的可燃气体介质运动相比,激波对加快可燃气体介质运动的影响可以忽略。最后,通过高速摄影实验验证了激波对灭火效果的影响是可以忽略的。因此,冷激波系统中,激波对灭火效果和周边环境的影响是可以忽略的。     

Experimental study of planar shock wave interactions with dense packed sand wall

A dense packed sand wall is impacted by a planar shock wave in a horizontal shock tube to study the shock-sand wall interaction. The incident shock Mach number ranges from 2.18 to 2.38. A novel device for actively rupturing diaphragm is designed for the driver section of the shock tube. An apparatus for loading particles is machined by the electrical discharge cutting technique to create a dense packed particle wall. High-speed schlieren imaging system and synchronized pressure measurement system are used together to capture the wave structures and particle cloud velocity. The dynamic evolution model from dense packed particles to dense gas–solid cloud at the initial driving stage is established. The blockage and permeation effects of the sand wall work together and influence each other. The high pressure gas behind the incident shock wave blocked by the sand wall pushes the upstream front of the wall forward like a piston. Meanwhile, the high speed gas permeating through the sand wall drags the sands of the most downstream layer forward. The incident shock strength, initial sand wall thickness and particle diameter are varied respectively to investigate the shock attenuation and the wall acceleration. Increasing the sands diameter or mixing in small diameter sands can significantly attenuate the incident shock. The smaller particles or the particles in thinner wall can be dispersed into a larger range in the process of transform from dense packed particles to dense gas–solid cloud. Moreover, the stronger incident shock can disperse the particles into a larger region.     

Dense particle cloud dispersion by a shock wave

A dense particle flow is generated by the interaction of a shock wave with an initially stationary packed granular bed. High-speed particle dispersion research is motivated by the energy release enhancement of explosives containing solid particles. The initial packed granular bed is produced by compressing loose powder into a wafer with a particle volume fraction of $\phi _\mathrm{p} = 0.48$ . The wafer is positioned inside the shock tube, uniformly filling the entire cross-section. This results in a clean experiment where no flow obstructing support structures are present. Through high-speed shadowgraph imaging and pressure measurements along the length of the channel, detailed information about the particle shock interaction was obtained. Due to the limited strength of the incident shock wave, no transmitted shock wave is produced. The initial solid-like response of the particle wafer acceleration forms a series of compression waves that eventually coalesce to form a shock wave. Breakup is initiated along the periphery of the wafer as the result of shear that forms due to the fixed boundary condition. Particle breakup is initiated by local failure sites that result in the formation of particle jets that extend ahead of the accelerating, largely intact, wafer core. In a circular tube, the failure sites are uniformly distributed along the wafer circumference. In a square channel, the failure sites, and the subsequent particle jets, initially form at the corners due to the enhanced shear. The wafer breakup subsequently spreads to the edges forming a highly non-uniform particle cloud.     

激波驱动下固体颗粒抛撒的实验研究

本文使用阴影照相技术、高速摄像技术及压力测试手段,实验记录和研究了激波与固体颗粒群的作用及激波作用后固体颗粒群的抛撒和云团的形成过程.结果表明:在激波与固体颗粒群作用过程中,存在着清晰的激波透射、反射及绕射现象,同时激波强度在作用后有明显的下降趋势;在固体颗粒抛撒及云团形成过程中,实验发现对同一粒径的颗粒抛撒来说,抛撒的颗粒群质量越大,云团形成的均匀性及稳定性越好,而对不同粒径的颗粒群来说,粒径越大,形成的云.团集中性越强.     

攻角对聚醚醚酮/泡沫镍双连续复合材料料浆冲蚀行为的影响

聚醚醚酮(PEEK)/泡沫镍双连续复合材料是一种新型复合材料，它是由比强度高的PEEK树脂(基体相)和韧性较高的泡沫镍(增强相)牢固结合而成，具有两相相互连通、拓扑连续和各向同性等特点. 使用孔径为100 PPI(每英寸孔隙数目)的泡沫镍与PEEK树脂混合，采用热压成型技术制备了PEEK/泡沫镍双连续复合材料(PEEK-Ni). 利用喷射式腐蚀冲蚀试验设备研究了纯PEEK树脂、金属镍和PEEK-Ni在5个攻角下(30°、45°、60°、75°和90°)的料浆冲蚀行为. 使用ANSYS Fluent有限元仿真软件对不同攻角下料浆的冲蚀过程进行建模和仿真，并设置了边界条件. 试验和仿真的结果均表明:随着攻角增加，冲蚀损伤形貌由月牙形损伤区域变为U型损伤区域，并最终发展成为围绕驻点的环形损伤区域，试验和仿真能相互吻合. 由于泡沫镍具有遮挡效应和协同效应，PEEK-Ni比纯PEEK具有更低的冲蚀损伤量，且对攻角不敏感.      

Reflection of a ring shock wave from a rigid wall

A new type of an implosion has been observed experimentally and simulated in a numerical calculation: the formation of a quasi-spherical converging shock wave after the reflection of a ring shock wave from a solid wall. The conversion of the ring shock wave into the quasi-spherical converging shock wave intensifies the local implosion properties.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

冲击拉伸实验装置的研制及其试验研究

材料动力学试验技术远比准静态力学中的复杂,为了模拟各种速率的冲击加载过程,试验装置设计就成为关键问题之一.特别是针对材料动态拉伸性能的测试,目前的冲击拉伸装置还没有统一标准,因此本文基于一维弹性应力波原理设计了一套双气室间接杆-杆型冲击拉伸试验装置.该装置采用了双气室对称布置的方式,通过气体转换器实现气路的转换,克服了现有气动式冲击拉伸设备结构复杂、密封要求严格的缺点.本文利用该装置对2A12T4铝合金试件的冲击拉伸性能进行了测试,并数值分析了应力波在杆系和试件中的传播效应.通过试验测试和数值分析论证了该冲击拉伸装置实验的可靠性和设计的合理性.     

Erosion of Ductile and Brittle Materials

The fundamental mechanisms of erosion by solid particle impact were investigated in both brittle and ductile materials. A review of the literature of erosion theoretical models indicated various different models. The most important ones were used to reproduce experimental tests concerning the erosion by solid particle impingement using gas jets. If supported by an appropriate tuning of certain parameters, they perform well. Since a continuous tuning of these parameters is required, experiment based theoretical models seem to be inappropriate in the development of advanced materials for high temperature applications. Consequently, we have developed a new approach based on the finite element method. Since it only requires the knowledge of the main mechanical properties as a function of the temperature, it seems suitable for the erosion rate evaluation in a wide range of applications. Early assessment results, compared to experimental erosion tests conducted at room temperature, showed good predictive capabilities which are even better than theoretical models.