Effect of reinforcing submicron SiC particles on the wear process of electrolytic NiP coatings

The effect of submicron silicon carbide frictional strengthening admixtures and heat treatment on the wear process of nickel phosphide coatings obtained by electrolytic deposition is studied. Despite the heat treatment and admixtures of silicon carbides, the wear of the coatings is of abrasion-oxidizing nature; in the case of NiP-SiC composite coatings, the oxide films formed during the friction process do not exhibit the shield effect; these films show a considerable effect on the wear of silicon-free NiP coatings. The silicon carbide admixtures increase the hardness of the electrolytic coatings but prevent the oxide films formed in the frictional process from attaching to the contact surface. Annealing of the coating reduces the wear rate. In the process of heat treatment, the crystalline phase Ni₃P is formed in the NiP matrix, increasing the coating hardness. At the same time, in the process of annealing of NiP-SiC composite coatings, the NiP matrix cracks around the silicon carbides. As a result, silicon carbides are extracted in the frictional process and the wear rate of the NiP-SiC composite coating grows.     

Motion analysis on the particles in a magnetic field detector

This paper, as the title indicates, deals with the depositing mechanism of the particles under the magnetic field in the lubricant for on-line ferrograph or oil analysis. Lubricant, containing ferromagnetic particles, is taken as the multiphasic ferromagnetic fluid in ferrograph detecting. By measuring and regressing, the distribution formulas of magnetic density and magnetic density gradient of an electromagnet are gained. The variance law of viscosity of lubricant in the non-uniform magnetic field is studied and a viscosity formula is put forward. The motion law of ferromagnetic particles in the non-uniform magnetic field is studied and a standpoint is put forward, which is that the ferromagnetic particles cannot achieve a constant sinking velocity in a non-uniform magnetic field. The factors influencing particles motion, such as particle diameter, ratio of particles volume and air bubbles, are also studied. Some results are obtained and discussed, which are of practical significance in the research and design of on-line ferrograph and other methods of on-line oil monitoring.     

Improving the accuracy of single radioactive particle technique for flow velocity measurements

An original method of flow velocity estimation for a radioactive particle technique is presented. It is based on exchanging measured pulses into cumulative signals, and determination of time delay as time difference of occurrences of inflection points of cumulative curves. To determine the inflection points, a suitable algorithm is proposed. The preliminary results show that the proposed method is especially more precise than the classical cross-correlation approach. The preliminary results show that this method can be successfully applied in a laminar flow with any type of fluid, and can without limitation be applied for different types of radioactive detectors.     

Enhanced measurement capability of a digital particle holographic system for flow field measurements

To enhance the capability of digital particle holography as a tool for flow field measurements, several effective methods are developed. The correlation coefficient method was used to accurately locate the focal plane of particles and the optimal factors of this method were discussed. To remove noises and improve the quality of holograms and reconstructed images, the Wiener filter was adopted. The two-threshold and image segmentation methods were used to obtain high quality binary images from which we can get good results of particle extraction. Based on the above methods, an in-line digital particle holographic system was applied to channel flow field and the axial velocities of channel flow were measured. The feasibility of these methods is verified by quantitative measurement results which are in good agreement with the theoretical predictions.     

Experimental verification of a model of erosion due to the impact of rigid single angular particles on fully plastic targets

A previously described rigid-plastic model of the erosion of ductile targets by the impact of single angular particles was experimentally verified over a wide range of particle angularities, incident angles of attack, and incident orientation angles. The model assumes that the particle is perfectly rigid and thus is non-deforming, while the target material response is fully plastic, so that elastic rebound effects are neglected.Measurements of particle rebound kinematics, crater volume, and crater shape revealed generally good agreement with those predicted by the rigid-plastic model, and erosion mechanisms resulting from particles tumbling either forwards or backwards, were identified. For highly angular particles, target material removal sometimes occurred due to tunnelling of the particles below the target surface, leading to early break-off of a machined chip, behaviour that could not be predicted by the rigid-plastic model. Besides providing insights into fundamental erosion mechanisms, the results of the present study can be used to predict particle rebound kinematics, crucial for simulations of erosive streams which take into account interference between incident and rebounding particles.     

散射光法探测微米群粒子场粒子性质的应用研究

提出了用激光进行散射光分析来探知未知群粒子场粒子性质的新的方法.实验中用直径0.22 μm和0.494 μm的粒子分别与过滤的蒸馏水制成不同浓度的悬浮液作为散射粒子场,并采用了波长为0.632 8 μm的激光.通过理论分析,并进行实验研究发现,在微米级群体粒子散射场中,粒子侧向散射光的退偏振情况与粒子的直径密切相关,直径大的粒子其水平方向线偏振度远小于直径小的粒子,而其垂直方向的线偏振度却远大于直径小的粒子.此结论可用作探测未知群粒子场粒子性质特别是用于粒子大小区别判断.     

Effects of particle entrainment on heat transfer past particles in an oscillating flow

In order to investigate the effect of the particle entrainment on the heat transfer past paricles entrained in an oscillating flow with and without a steady velcoity, the two dimensional, unsteady, laminar conservation equations for mass, momentum and energy transport in the gas phase are solved numerically in spherical coordinates. The particle momentum equation is also solved simultaneously with the gas phase equations. The numerical solution gives the particle velocity variation as well as the gas phase velocity and temperature distribution as a function of time. The local and space-averaged Nusseit number with particle entrainment is compared with that without particle entrainment. In the case of an oscillating flow with a steady velocity, the values of the space-averaged Nusselt number with particle entrainment are lower than those without particle entrainment at frequencies of 50 and 2000 Hz since the moving particle is entrained in the steady velocity. In the case of an oscillating flow without a steady velocity, the space-averaged Nusselt number with entrainment at a frequency of 50 Hz is slightly lower than that without particle entrainment, with a phase lag. At 2000 Hz, the space-averaged Nusselt number with and without particle entrainment is almost the same, due to very small particle entrainment.     

Measurement and analysis of the flow field in a pulsatile ventricularassist device

A pneumatically driven ventricular assist device (VAD) of unconventional geometry, designed to mitigate adverse haemostatic phenomena by optimization of flow patterns, was investigated using two-component laser Doppler anemometry (LDA). Data were taken on a rectilinear grid over two orthogonal traverses, allowing synthesis of three-dimensional velocity vectors over most of the grid. The resulting data were examined by two-dimensional and three-dimensional static and animated computer graphic visualizations of the time-varying vector fields. This analysis revealed illuminating and previously unobserved features of the complex flow fields within pulsatile VADs and identified design considerations that bear upon minimization of turbulence and of flow recirculation and stasis. The findings of this study suggest that, while total abolition of undesirable flow phenomena in a diaphragm-type blood pump is probably impossible, comprehensive investigation in vitro can engender considerable improvements in the efficacy of a device.     

A numerical analysis on three-dimensional flow field in a supersonic bump-type inlet

The characteristic of a supersonic inlet system with three-dimensional bump which is substituted for the diverter or conventional ramp-type compression systems has been studied numerically. A comprehensive numerical analysis has been performed to understand the threedimensional flow field including shock/boundary layer interaction and growth of turbulent boundary layer that might occur around a three-dimensional bump in a supersonic inlet. The current numerical simulations showed the supersonic bump-type inlet which is modified from a conventional ramp-type inlet to control shock/boundary layer interaction effectively and evolved to maximize inlet performance.     

Magnetic field effect on fluid flow characteristics in a pipe for laminar flow

The influence of a magnetic field on the skin friction factor of steady fully-developed laminar flow through a pipe was studied experimentally. A mathematical model was introduced and a finite difference scheme used to solve the governing equations in terms of vorticity-stream function. The model predictions agree favourably with experimental results. It is observed that the pressure drop varies in proportion to the square of the product of the magnetic field and the sine of the magnetic field angle. Also, the pressure drop is proportional to the flow rate. This situation is similar to what applies in the absence of a magnetic field. It is found that a transverse magnetic field changes the axial velocity profile from the parabolic to a relatively flat shape. At first, the radial velocity rises more rapidly and then gradually decreases along the pipe until falling to zero. A numerical correlation can be written for the considerable distance required for the new axial velocity profile to establish. Owing to the changes taking place in the axial velocity profile, it exhibits a higher skin friction factor. The new axial velocity profile asymptotically approaches its limit as the Hartmann number becomes large.     

基于ABAQUS的单个颗粒与加工面碰撞对固液两相流加工的影响研究

针对固液两相流加工过程中磨粒如何影响加工效果的问题,提出了磨粒与工件之间的摩擦状况是直接影响抛光过程与抛光质量的重要因素的假设。根据实际加工的实验材料数据,利用ABAQUS非线性有限元分析软件,研究了单磨粒对工件表面的接触作用与材料去除的关系;然后搭建了固液两相流实验平台,对试验钢条进行了软性磨粒流加工。实验结果表明,加工表面的磨损分布比较均匀,表面的粗糙度明显降低,体现了固液两相流加工的有效性。研究结果表明,实际加工中加工表面在受到水平切削力和竖直挤压力共同作用下,产生了塑性变形继而发生切削磨损,最终提高了加工表面的抛光效果,达到了镜面级加工效果的目的,同时通过使用ABAQUS软件可从微观直接说明固液两相流无工具精密加工机理。     

采用流场分析提高涡轮流量传感器性能的研究

以10 mm口径液体涡轮流量传感器为研究对象,经过对传感器内部流场进行分析,提出通过减小靠近叶片顶端的叶片受力面积,提高传感器测量性能的方法。从对特性曲线的分析出发,结合传感器数学模型,提出了一种利用不同流量点的仪表系数平方差Δ(K~2)评价传感器性能的方法。在此基础上,结合CFD仿真和传感器样机实验测试,研究了不同叶轮叶片形状参数对传感器性能的影响。实验结果表明:改变叶轮叶片形状能有效提高传感器的测量性能,切角参数为0.25时,传感器性能最优;此方法同样适用于其他口径涡轮流量传感器结构的优化。     

极大流量工况下离心泵内部流场数值分析

针对离心泵极大流量工况下内部流动特性的问题,应用流体动力学软件Fluent,采用RNGκ-ε湍流模型与SIMPLEC算法,对某一高比转速离心泵内部流场进行了数值模拟,并与实验结果进行了比较。对比分析了4种不同流量工况下离心泵内部流体速度和压力分布以及离心泵的外特性。研究结果表明,在设计流量工况下,离心泵内部压力分布均匀,速度迹线平滑;较大流量工况下,蜗壳压力不断减小,速度分布不均匀;极大流量(1.7Qopt)工况下,蜗壳出口处出现局部负压现象,速度流线产生的漩涡增大,在扩散管局部位置流体受到冲击,容易出现回流现象。针对离心泵在不同工况下以及达到极大流量工况下内部流动随流量变化规律的研究,可为高比转速离心泵多工况优化设计、延长使用寿命提供参考。     

Experimental investigation on the fiber preform deformation due to mold closure for composites processing

In liquid composite molding processes, e.g., resin transfer molding, fiber preforms deform when mold is closed. This deformation of fiber preform due to mold closure causes inconsistencies to the permeability, and thus has a negative impact on resin flow. The variations in resin flow cause defects, e.g., dry spots and voids, resin-rich surfaces/zones, fiber distortions, which result in large variations in the product dimensions and mechanical performance. Thus, good understanding of the effects of process parameters on the deformation of fiber preform is necessary for developing high-quality affordable composites. An experimental study on the deformation of fiber preform for making angle-shaped composite parts is presented in this paper. The effects of enclosed angle, radius, fiber volume fraction, and stacking sequence were studied efficiently using design of experiments (DOE). Two open-channel molds were designed and fabricated for varying the design parameters. In each experiment run, the fiber preform was loaded into the mold and the mold was closed. The gaps formed between the fiber preform and inner mold surface were visually inspected by a microscope, and quantitatively characterized. The data were then analyzed. It is shown from the experiments that gaps occur at two locations: at corner radii and beside corner radii. The following conclusions are drawn from this experimental study: (1) fiber volume fraction is the most significant factor affecting the gaps at corner radii, and the gap thickness decreases with increasing fiber volume fraction; (2) the gap thickness decreases with increasing radius; and (3) the gap thickness of unidirectional preforms is larger than that of the cross-ply preforms.     

Large-eddy simulation and acoustic analysis of a turbulent flow field in a swirl-stabilized combustor

To conduct a comprehensive study on the flow characteristics and acoustic oscillation in a gas turbine combustor, a 3D large-eddy simulation (LES) was implemented. The formulation consists of the Favre-filtered conservation equations of mass, momentum, and energy. The subgrid-scale dynamics are modeled using a compressible flow version of the Smagorinsky model. To investigate the dominant coherent structure, the proper orthogonal decomposition (POD) method was used for post-processing. The combustor of concern is the LM6000, lean-premixed dry low-NOx annular combustor, developed by General Electric Aircraft Engines (GEAE). Four important characteristics of swirl flow are visualized: vortex breakdown, procession and dissipation of vortical structures, recirculation zones, and helical waves immediately downstream of the swirl injector. It is shown that the turbulent motion of swirl flow directly affects acoustic oscillation through the cycle and spectral analysis. The four most dominant acoustic modes are extracted from the flow field by the POD analysis. The transverse modes in the y and z directions are dominant in all four modes, since the pressure fields are significantly affected by swirl flow.     

Ion slip effect on the flow due to a rotating disk with heat transfer

The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important effects on the velocity distribution as well as the heat transfer.     

Ion slip effect on the flow due to a rotating disk with heat transfer

The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important effects on the velocity distribution as well as the heat transfer. On leave from: Department of Engineering Math. and physics, Fac. of Engineering, El-Fayoum University, El-Fayoum, Egypt.     

MOCVD反应器内部气体流动模拟分析

以金属有机化学气相沉积（MOCVD）反应器沉积GaN为对象,建立了反应器内部数学模型.通过应用GAMBIT软件划分复杂模型的基础上,对新颖的反应器的输运过程进行了二维数值模拟的研究,计算了反应器中流场的分布.根据对模拟结果的分析可知,在低于常压和反应器进口距加热器距离较小的工况下,反应器内的输运过程比较稳定,满足制备薄膜所需的层流特征.     

Analysis of the roll hunting force due to hardness in a hot rolling process

A hot rolling operation is performed to alter the thickness of a metal by passing the material through a pair of rollers, forming a gap that is somewhat narrower than the thickness of the material. Therefore, the quality of the product is a function of the pressure applied by the rollers. However, in this process, a roll hunting force occurs in which the rolling force is irregularly changed during the rotation of the rollers due to various complex mechanisms, which include roll surface hardness, difference in rotational speed between rolls, heat treatment conditions, and roll wear. In this study, roll wear tests were conducted to analyze the roll hunting force caused by variation in the hardness of the work roll. The friction coefficient of the work roll was then examined based on hardness. Then, a two-dimensional finite element model was constructed to investigate the roll hunting force as a function of the change in friction coefficient of the work roll. This finite element model was verified in relation to the theoretical rolling expression. Finite element model analysis was performed for three friction coefficients, and the effect of the roll hunting force was determined based on the reduction ratio and temperature. In addition, the wear depth of the work roll by the hardness was predicted. The influence of the abrasion of the work roll on the hunting force was analyzed.

     

Stochastic hybrid numerical method for transient analysis of stress field in functionally graded thick hollow cylinders subjected to shock loading

This investigation aims to study the random stresses in a functionally graded (FG) thick hollow cylinder with uncertain material properties subjected to mechanical shock loading using a hybrid numerical method. The mechanical properties are considered to vary across thickness of FG cylinder as a nonlinear power function of radius. The stresses are obtained by solving Navier equation and using Galerkin finite element and Newmark finite difference methods. The Monte Carlo simulation is used to generate the random mechanical properties for the problem. The failure probabilities and time history analysis of stresses are determined for various coefficient of variation considering various grading patterns of mechanical properties. The presented hybrid numerical method is effective, with high capability for stochastic analysis of dynamic and transient analysis of FG structures with various boundary conditions.