磨料水射流冲蚀金属损伤形貌特征及机理研究

针对前混合磨料水射流冲蚀过程,进行了冲蚀试验及仿真研究.从试验中得到了材料冲蚀损伤形貌特征.采用SPH耦合FEM方法建立相应的冲蚀模型,对材料冲蚀过程进行模拟分析,揭示了材料损伤形貌特征产生的机理.结果表明:随着冲蚀深度的增加,磨料颗粒的冲蚀动能逐渐减小,冲蚀角度逐渐增大,材料冲蚀损伤由微切削和微犁削逐渐变为冲击变形,材料冲蚀损伤断面的形貌特征逐渐恶化,具体表现为拖尾角和表面粗糙度逐渐增大.不同金属材料损伤断面形貌特征具有相似性,但是金属材料属性的差异会对磨料冲蚀过程产生影响,导致条纹在材料损伤断面上的分布和条纹角度出现差异.由于材料损伤形貌特征受控于磨料颗粒运动特性,因此材料冲蚀断面质量改善应该从改变磨料颗粒运动特性角度出发,这为进一步研究材料冲蚀断面质量改进奠定了理论基础.     

风沙环境下钢结构涂层低角度冲蚀特性研究

针对风沙环境中钢结构涂层长期受冲蚀,涂层破坏直接降低钢结构体系耐久性的现状,采用能模拟风沙环境的气流挟沙喷射法对钢结构涂层试件进行了低角度冲蚀试验,用失重测量法测定涂层冲蚀失重量与沙剂量和冲击速度关系,进而评定冲蚀程度,用扫描电镜(SEM)观测分析涂层冲蚀区的微观形貌来分析冲蚀机理,并提出了涂层冲蚀程度评价计算公式.结果表明:涂层冲蚀失重量随沙剂量和冲击速度的增大而增加;低角度冲蚀主要为微切削作用,材料硬度起决定因素,高角度冲蚀主要为冲蚀挤压变形作用,材料韧性起决定作用,由于涂层材料硬度低而韧性高,故在低冲角下其受冲蚀程度严重;验证了评价计算公式用于评价涂层冲蚀程度的可靠性.研究结果将为准确评价风沙区钢结构体系耐久性提供依据.     

冲蚀地形上悬跨海底管线涡激振动试验研究

为了给海底管线服役期间的安全评估提供科学依据,基于水弹性相似关系,对海底管线服役期间常见水流环境条件下,冲蚀地形上悬跨弹性海底管线涡激振动进行试验研究.采用粘贴于管线内壁的应变片测量振动过程中的应变.通过与平底地形上相关研究结果进行对比分析发现:冲蚀地形上悬跨海底管线涡激振动强度与振动频率均受到冲蚀地形的影响;振动强度随水流折减速度的变化比平底地形要快,在相对冲坑长(悬跨长)L/D为20与L/D为35时涡激振动强度的差别较平底地形上悬跨管线要小得多;管线垂向振动频率随冲蚀地形冲坑长度的减少而增大;冲蚀地形上悬跨管线周围的斯特劳哈尔数St在0.21左右.比相同雷诺数下平底地形上悬跨管线周围St数略大.     

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.      

泡沫镍/聚氨酯双连续复合材料的液滴冲蚀行为研究

利用液滴冲蚀试验装置,开展了泡沫镍/聚氨酯双连续复合材料和纯聚氨酯的液滴冲蚀试验研究,并采用PIV系统,测量了液滴冲蚀中液滴速度和直径. 结果表明:随着冲击能量的增加,复合材料表现出比纯聚氨酯更好的抗液滴冲蚀性能;泡沫镍结构参数对复合材料的液滴冲蚀行为有重要影响,泡沫镍孔径越小、体密度越大,复合材料的抗冲蚀能力越强;密集的金属骨架能有效阻挡高速液滴的破坏作用,并为树脂基体提供较强的阴影保护效应和地毯保护效应,显著提高复合材料的抗冲蚀性能.      

等径角挤压后Ti5553钛合金的冲蚀磨损机理演变

本文中系统研究了经等径角挤压(ECAE)处理后的Ti5553钛合金在海砂环境中的冲蚀磨损机理演变历程和失效原因.发现Ti5553钛合金在高角度冲蚀工况下,其冲蚀磨损机理从初期的微切削转变为冲击挤压变形,并保持稳定;合金显微组织中弥散的α相以及ECAE工艺影响了冲蚀机理演变过程及冲蚀磨损程度;提高合金的强度、韧塑性对于抵抗冲蚀磨损起到了促进作用.     

砂粒对多相流弯管冲蚀的影响因素分析

冲蚀是一个管壁材料受固相颗粒重复撞击而剥落,又伴随着腐蚀的复杂力学过程。冲蚀严重时可能引起管道失效或泄漏,从而产生经济损失和环境污染。为了研究多相流弯管冲蚀的基本规律和主要影响因素,本文基于自行设计的循环管路进行了水-砂两相流对弯管段碳钢贴片的冲蚀试验。基于弯道流动特征分析、扫描电镜观察和贴片的冲蚀速率估计,得到了弯管段壁面的主要损伤特征。弯管段壁面可分为四个区:外拱璧、内拱璧和左右两颊壁面。外拱璧处试验贴片的主要损伤特征为大量压痕、划痕和近圆形的蚀坑分布,其壁面减薄的主要机制为弯道流动中砂粒的多次高速冲击和切削作用;而内拱璧处的损伤特征主要是蚀坑周围包围着腐蚀产物,流动中的砂粒低速冲击和腐蚀氧化作用更为明显;两颊壁面处冲刷磨损与腐蚀增重作用相当。此外,分析了砂粒粒径、含砂量以及贴片材质对冲蚀速率的影响。大粒径及较高含砂量对冲蚀速率均起到增强作用;壁面的材料属性有差异,表面形貌的损伤特征亦有不同。     

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.     

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.      

预置圆孔膨胀环动态断裂行为研究

利用中心线起爆膨胀环加载技术,采用分幅摄影技术观测了20号钢圆环在准一维拉伸作用下,预置圆孔缺陷临近区域的动态断裂特征。获得了高应变率下圆孔的变形、裂纹的萌生及扩展过程。并采用LS-DYNA3D有限元程序分步建模,将驱动器对膨胀环的冲击压力简化为直接作用于圆环内壁的压力历史,以此模拟了整个断裂过程。通过实验图像,得到裂纹尖端的位移以及速度随时间变化的曲线。结果表明,宏观可见裂纹出现于应力集中最大处,裂纹扩展速度随时间振荡,数值模拟与实验结果吻合较好。     

含砂流对弯管段冲蚀的机理分析

管道的弯管段、闸阀等处常常面临含砂流动的冲蚀磨损而导致管壁减薄或泄漏。为研究弯管段冲蚀磨损的主要机制,进行了加入5%石英砂的固液两相管流循环试验。试验按砂粒粒径分组,主要观测布置在弯管段的一组碳钢贴片在2~3小时后的壁面冲蚀特征。用失重法计算各贴片的冲蚀速率,基于扫描电镜(SEM)研究了贴片表面的损伤形貌。冲蚀后的贴片表面既有犁沟、挤压凹坑及划痕,亦有圆形蚀坑。能谱分析(EDS)显示有一定量的铁氧化物,且不同位置处的贴片失重率有正有负,由此可见导致贴片表面破坏的机制既包括切削、挤压和二次冲击等含沙流流动的机械作用,也伴随着腐蚀作用。这两种机制在弯管各区有不同的体现,且受砂粒粒径的影响。用数值模拟的两相流冲蚀弯管段流场压力和颗粒分布特征做了验证。结果表明弯管段的壁面损伤机制在外拱壁面以颗粒冲击和切削为主,在内拱璧面则以氧化腐蚀为主。     

A plane turbulent wall jet on a fully rough surface

The mean velocity field and skin friction characteristics of a plane turbulent wall jet on a smooth and a fully rough surface were studied using Particle Image Velocimetry. The Reynolds number based on the slot height and the exit velocity of the jet was Re = 13,400 and the nominal size of the roughness was k = 0.44 mm. For this Reynolds number and size of roughness element, the flow was in the fully rough regime. The surface roughness results in a distinct change in the shape of the mean velocity profile when scaled in outer coordinates, i.e. using the maximum velocity and outer half-width as the relevant velocity and length scales, respectively. Using inner coordinates, the mean velocity in the lower region of the inner layer was consistent with a logarithmic profile which characterizes the overlap region of a turbulent boundary layer; for the rough wall case, the velocity profile was shifted downward due to the enhanced wall shear stress. For the fully rough flow, the decay rate of the maximum velocity of the wall jet is increased, and the skin friction coefficient is much larger than for the smooth wall case. The inner layer is also thicker for the rough wall case. The effects of surface roughness were observed to penetrate into the outer layer and slightly enhance the spread rate for the outer half-width, which was not observed in most other studies of transitionally rough wall jet flows.     

Experimental study of aortic flow in the ascending aorta via Particle Tracking Velocimetry

A three-dimensional, pulsatile flow in a realistic phantom of a human ascending aorta with compliant walls is investigated in vitro. Three-Dimensional Particle Tracking Velocimetry (3D-PTV), an image-based, non-intrusive measuring method is used to analyze the aortic flow. The flow velocities and the turbulent fluctuations are determined. The velocity profile at the inlet of the ascending aorta is relatively flat with a skewed profile toward the inner aortic wall in the early systole. In the diastolic phase, a bidirectional flow is observed with a pronounced retrograde flow developing along the inner aortic wall, whereas the antegrade flow migrates toward the outer wall of the aorta. The spatial and temporal evolution of the vorticity field shows that the vortices begin developing along the inner wall during the deceleration phase and attenuate in the diastolic phase. The change in the cross-sectional area is more distinct distal to the inlet cross section. The mean kinetic energy is maximal in the peak systole, whereas the turbulent kinetic energy increases in the deceleration phase and reaches a maximum in the beginning of the diastolic phase. Finally, in a Lagrangian analysis, the temporal evolution of particle dispersion was studied. It shows that the dispersion is higher in the deceleration phase and in the beginning of the diastole, whereas in systole, it is smaller but non-negligible.     

Experimental and CFD investigation of flow behavior and sand erosion pattern in a horizontal pipe bend under annular flow

The internal erosion of pipelines in oil and gas storage and transportation engineering is highly risky. High gas velocity of annular flow entrained sand will cause damage to the pipelines, and may further result in thinning of the wall. If this damage lasts for a long time, it may cause pipeline leakage and cause huge economic losses and environmental problems. In this research, an experimental device for studying multiphase flow erosion is designed, including an erosion loop and an experimental elbow that can test the erosion rate. The annular flow state and pipe wall erosion morphology can also be tested by the device. The computational fluid dynamics (CFD) method is combined with the experiment to further study the annular flow erosion mechanism in the pipeline. The relationship between gas-liquid-solid distribution and erosion profile was studied. The results show that the most eroded region occurs between 22.5° and 45° in the axial angle direction and between 90° and 135° in the circumferential angle direction of the elbow. The pits and deep scratches form on the surface of the sample after the sand collision.     

Experimental studies of turbulence in mercury flows with transverse magnetic fields

The differential pressure reading from a static hole pair is utilized for determination of the local wall shear stress. Both the hole diameter and forward-facing angle are varied to test the sensitivity of the device. The static hole pair in tested in a two-dimensional zero pressure gradient turbulent boundary layer on a smooth surface. The calibrating values for the local wall shear is determined from the universal scaling laws for the mean velocity profile in the inner part of the turbulent boundary layer. The static hole pair is found to be sensitive to imperfections in the manufacturing process, and needs an individual calibration in order to make accurate measurements of the local skin friction possible.     

Numerical Simulation of Turbulent Flow in Concentric Annuli

In this paper we consider a fully developed turbulent flow in a round pipe with a small inner annulus. The diameter of the inner annulus is less than 10% of the diameter of the outer pipe. As a consequence, the surface area of the inner pipe compared to the outer pipe is small. The friction exerted by the wall on the flow is proportional to the surface area and the wall shear stress. Due to the small surface area of the inner annulus the additional stress on the flow due to the presence of the annulus may expected to be negligible. However, it will be shown that the inner annulus drastically changes the flow patterns and gives rise to unexpected scaling properties. In previous studies (Chung et al., Int J Heat Fluid Flow 23:426–440, 2002; Churchill and Chan, AIChE J 41:2513–2521, 1995) it was argued that radial position of the point of zero shear stress does not coincide with the radial location of the point of maximum axial velocity. In our direct numerical simulations we observe a coincidence of these points within the numerical accuracy of our model. It is shown that the velocity profile close to the inner annulus is logarithmic.     

基于流固耦合的燃气冲刷烧蚀内膛特性分析

火炮发射时，火药燃气与身管间发生剧烈的传热传质作用是导致身管烧蚀的重要因素。为了研究某155 mm火炮中高温高压高速的燃气流对身管的烧蚀特性，采用CFD流固耦合方法，建立了发射过程中的身管非稳态流动传热模型，并根据炮钢在不同温度下的烧蚀特点，将烧蚀过程分为热化学烧蚀和熔化烧蚀，建立了分段烧蚀模型。计算结果表明，身管内壁温度随时间的增加先迅速增大，随后逐渐降低。整体上，内壁温度随身管轴向距离的增大而逐渐降低。身管膛线起始区域的壁面温度最高，其烧蚀是熔化和热化学烧蚀共同导致的，而线膛部的大部分区域仅发生了热化学烧蚀。总烧蚀量随着身管轴向距离的增大而逐渐降低，膛线起始部的烧蚀最为严重，单发总烧蚀量（常温）为5.06μm。同时分析了不同工况对身管烧蚀特性的影响，发现最大烧蚀量与初始壁面温度呈现很强的正相关性，温度的升高会加剧身管的烧蚀。     

Particulate Dispersion in a Turbulent Serpentine Channel

Particulate dispersion in an S-shaped duct, with periodicity between inlet and exit, is studied by direct numerical simulation. Stokes numbers range from 0.125 to 6.0. In a straight, turbulent channel flow, eddies are responsible for particulate impact. Turbophoresis causes a mean drift toward the wall. In a curved channel, particle inertia can be the dominant cause of impact. Above the lowest Stokes number, particles form into a plume that leaves the inner bend and flows toward the outer wall. Turbulence then disperses the plume. Heavier particles cross the bend and reflect from the outer wall, forming a high concentration layer near the surface. The heaviest particles reflect again from the wall and are dispersed across the duct by turbulence. An empirical formula is used to analyze the propensity for particle impacts to erode the wall. The region of maximum erosion is not the region of maximum number of impacts, nor is it where the impact velocity is highest: the impact angle determines where erosion is largest.     

90°弯管内气固两相湍流流动的数值研究

利用两相湍流KET模型对90°弯管内气固两相湍流流动进行了数值模拟,得到了弯管内两相流动的一些规律,并提出用颗粒动理学压力来定性表征弯管内磨损严重部位,为管道抗磨损设计提供了一定的理论依据。