Simultaneous measurement of particle and fluid velocities in particle-laden flows

For the velocity measurement in a particle-laden fluid flow, the fluid velocity and the inherently dispersed particle velocity can be analyzed by using PIV and PTV, respectively. Since the PIV result statistically represents the average displacement of all the particles in a PIV image, it is inevitable that the PIV result includes the influence of the dispersed particles’ displacement if a single CCD camera is used to simultaneously measure the fluid velocity and the dispersed particle velocity. The influence of dispersed particles should be excluded before the PIV analysis in order to evaluate the fluid velocity accurately. In this study, the optimum replacement brightness of dispersed particles to minimize the false influence of dispersed particles on the PIV analysis was theoretically derived. Simulation results show that the modification of dispersed particle brightness can significantly reduce the PIV error caused by the dispersed particles. This modification method was also verified in the analysis of an actual experimental case of the particle-laden fluid flow in a triangular grooved channel.     

An ant colony optimization based stereoscopic particle pairing algorithm for three-dimensional particle tracking velocimetry

An ant colony optimization (ACO) based stereoscopic particle matching algorithm has been developed for three-dimensional (3-D) particle tracking velocimetry (PTV). In a stereoscopic particle pairing process, each individual particle in the left camera frame should be uniquely paired with the most probable correct partner in the right camera frame or vice-versa for evaluating the exact 3-D coordinate of the particles. In the present work, a new algorithm based on an ant colony optimization has been proposed for this stereoscopic particle matching. The algorithm is tested with various standard 3-D particle image velocimetry (PIV) images of the Visualization Society of Japan (VSJ) and the matching results show that the performance of the stereoscopic particle pairing is improved by applying proposed ACO techniques in comparison to the conventional nearest-neighbor particle pairing method of 3-D stereoscopic PTV.     

Full factorial investigation on the erosion-corrosion resistance of UNS S31603

The interactions that occur when erosion and corrosion act simultaneously are extremely complex and are often difficult to interpret. These interactions generate either a synergistic or antagonistic material loss effect for a particular material in a certain environment. The level of interaction between impact energy, number of impacts, fluid temperature, material properties, fluid flow and electrochemical properties severely complicates the analysis of erosion-corrosion wear rates. This paper investigates the interaction between the main parameters influencing erosion-corrosion. A combination of statistical analysis and interaction contour plots has been employed to obtain in-depth understanding of the variables influencing erosion-corrosion, namely particle velocity, sand size, sand concentration and fluid temperature. An empirical equation has been derived from test results to describe the relationship between the test parameters. Analysis of the residuals versus predicted erosion-corrosion shows a normalized distribution and thereby confirms the suitability of this model. Velocity was found to have the strongest influence on erosion-corrosion rate followed by sand concentration, temperature and finally sand size, which had the least significant effect. SEM surface features show that the increase in sand concentration causes the surface to be covered with a higher number of impact craters and lips indicating a linear relationship between the two. The SEM micrographs also show that the increase in sand size produces deeper craters and more prominent lips compared to fine sized particles where the particles tend to graze the surface without sufficient kinetic energy to plastically deform the material surface.     

Erosion of Low-Carbon Steel by Coal Particles

The erosion of low-carbon steel, in the annealed and water-quenched condition, by coal particles, has been studied as a function of particle size, velocity, and angle of impingement. It was found that both unicrostructures, pearlitic and martensitic, showed a maximum erosion at an angle of impingement of between 20 and 30°. Under all condition of testing, the martensitic structure showed the higher rate of erosion. The coal particles were found to fracture on impact with the steel surfaces. The amount of fracture was found to increase will increased velocity and particle size. Erosion rate was found to increase with decreasing particle size and was related to particle velocity (V) through a power law relationship of the form: E = kVⁿ, where the exponent (n) has valves between 2.6 and 3.7. Scanning electron microscopy studies indicated that only the harder mineral constituents in the coal, such as pyrite and quartz, were responsible for the erosion of the steel.     

Erosion—corrosion characteristics of a 2.25 Cr-1 Mo steel exposed at low particle velocities

The erosion-corrosion characteristics of a 2.25 Cr-1 Mo steel at low particle velocities and elevated temperatures were determined using a nozzle type laboratory erosion tester. The tests were performed with 180–360 μm angular alumina particles at 60° angle of impingement at low particle velocities of 2.6–8.2 m/s and in the temperature interval 20–600°C. The steel was tested both in the as-received condition as well as in two preoxidized conditions. The erosion-corrosion rate of the steel, both in the as-received and in the preoxidized conditions, was found to increase with increasing particle velocity. In contrast, the wastage rates were relatively independent of temperature in the temperature range investigated, the only exception being specimens exposed to the lowest particle velocity (2.6 m/s) at the very highest temperature, i.e. 600°C, which displayed a drastic increase in wastage. Specimens preoxidized at 700°C exhibited a somewhat higher erosion rate compared with non-preoxidized specimens and specimens preoxidized at 500°C. Microscopy revealed four different major wastage mechanisms, i.e. (i) plastic deformation, cracking and micro chipping of surface material of a size corresponding to the area impinged by eroding particles, (ii) chipping of somewhat larger oxide fragments (up to 10–15 μm in diameter), (iii) chipping or spalling of relatively large oxide fragments (up to 30–50 μm in diameter), and (iv) spalling along the steel-oxide interface or within an oxide layer due to cohesive failure, of larger (up to 500 μm in diameter) oxide layer fragments. In the present study extensive spalling was only observed for non-preoxidized specimens exposed to the lowest particle velocity (2.6 m/s) and the two highest specimen temperatures (550°C and 600°C).     

Response surface regression analysis on FeCrBSi particle in-flight properties by plasma spray

This work discusses the interactive effects between every two of argon flow rate, voltage, and spray distance on in-flight particles by plasma spray and constructs models that can be used in predicting and analyzing average velocity and temperature. Results of the response surface methodology show that the interactive effects between voltage and spray distance on particle inflight properties are significant. For a given argon flow rate, particle velocity and temperature response surface are obviously bending, and a saddle point exists. With an increase in spray distance, the interactive effects between voltage and argon flow rate on particle in-flight properties appear gradually and then weaken. With an increase in voltage, the interactive effects between spray distance and argon flow rate on particle in-flight properties change from appearing to strengthening and then to weakening.     

A method for correcting discharge of boat-mounted ADCP measurements

GPS data are usually used to measure boat velocity during boat-mounted acoustic Doppler current profiler (ADCP) measurements when bottom tracking is biased by moving bed. GPS cannot provide consistently accurate boat velocity reference because of multipath errors, satellite signal reception problems, and heading errors. In addition, the computation of water velocity from an ADCP mounted onto a moving boat is a vector-algebra problem, thus the discharge calculation is subject to the compass error when GPS is used for boat velocity reference. This paper proposes a method for correcting discharge based on the idea that the discharge calculation is independent of the boat path. The processing of two sets of boat-mounted ADCP measurements integrated with differential GPS and non-differential GPS was simulated to verify the method. The results show that the proposed method performs well in both differential and non-differential GPS conditions. The relative errors range from 0.1% to 1.5% for all measurements with the mean relative errors of 0.7%. Analytical assessment of the GPS errors shows the proposed method is insensitive to the positioning accuracy of GPS, but positioning error of non-differential GPS may induce relative discharge error of more than 1% when the river or stream is narrow. On the contrary, a relatively small compass or heading error can cause a significant error in water velocity and discharge when using GPS as the boat velocity reference. Therefore, integrating a differential GPS and maintaining a slow boat speed are best practices for discharge measurement, especially for narrow streams or short boat paths.     

Novel streak-resolving algorithm for particle streak velocimetry

In this paper, a novel streak-resolving algorithm is proposed for particle streak velocimetry (PSV) to resolve velocity fields for a single image frame with multiple particle streaks. A model streak function, which was based on the temporal integral of the particle image intensity moving along its trajectory during the exposure period, was approximated using a multivariable least-square fit procedure to reconstruct the streak information and the corresponding particle trajectory. Lagrangian tracking was achieved, and the velocities were evaluated by differentiating the resolved particle trajectory with respect to time. Two types of flows, accelerating parallel flow and the rotational flow of Hill’s vortex, were used to generate synthetic streaks for the performance tests. Three types of relative error were defined and used to evaluate the performance of the algorithm in terms of statistical mean and standard deviation (SD) errors. The accuracy of the fitted streak parameters, such as particle image intensity and diameter, were also evaluated and compared. The results reveal that the error and SD were low if the image noise is below 1.0%; for noise levels of 5.0%, the error was up to 10% with an SD of up to 12%. The error and SD of the particle image intensity and particle image diameter for both flow types were also 0%–7% for clean and up to 12% for noisy images. The processing results for experimental streak images of flow past a cylinder reveal that these images can be resolved using the proposed algorithm with a residual mean error of 4.38 and an SD of 9.48. These results suggest that the proposed novel approach can be used to resolve velocity fields with only a single image frame and without expensive hardware for high-speed imaging and thus is suitable for diverse applications.     

Particle size effects on the slurry erosion of aluminium alloy (AA 6063)

The effect of particle size on erosion wear of aluminium alloy (AA 6063) has been investigated in a slurry pot tester. Eight different sized quartz particles with mean size varying between 37.5 and 655 μm have been used. The wear specimens are rotated inside the pot at 3 m/s velocity with orientation angle of 30° and 90° in a sand–water mixture of 20% concentration (by weight). It is seen that the erosion wear increases with increase in mean particle size. Two distinct mechanisms are noticed for mean particle size above 200 μm and below this size for the range of parameters under this investigation. It seems that a threshold kinetic energy of impacting particle may exist, which results in change in the wear rate at a particular particle size. The threshold kinetic energy for different operating conditions has been determined and its relation with the change in erosion mechanism is discussed.     

Cryogenic abrasive jet machining of polydimethylsiloxane at different temperatures

The temperature dependence of the solid particle erosion of polydimethylsiloxane (PDMS) using aluminum oxide particles was investigated between the temperatures of ?178 and 17 °C for a variety of angles of attack using a novel cryogenic abrasive jet machining apparatus. It was found that the most efficient machining of PDMS (volume removed per kinetic energy of erodent) occurred at approximately ?178 °C, at angles of attack between 30° and 60° from the surface. A previously developed surface evolution model was used to predict the size and shape of unmasked channels at various temperatures. A good agreement between the predicted and measured channel profiles was obtained when the average blasting temperature was between approximately ?127 and ?178 °C. At ?82 °C, the fit was poorer, probably because of an increase in particle embedding. Although it was demonstrated that PDMS could be machined at temperatures above its glass transition, the erosion rate increased by a factor of more than 10 when the machining temperature was below this point.     

Heat transfer in countercurrent gas-solid flow inside the vertical pipes

Heat transfer characteristics of the countercurrent gas-solid flow inside verical pipes has been investigated with the shell and tube type heat exchanger. Sand particles having the average particle diameter of 1.0 and 1.7mm were used. The effect of gas velocity and sand paticle flow rate on the heat transfer rate and the pressure drop were examined. At room temperatures, the predicted pressure drop agrees well with the experimental results when the larger sand particles are used. The results shows that there exists an optimum sand particle flow rate at which the heat transfer rate become maximum. The increase in the heat transfer coefficient due to sand particles was obtained up to 62%.     

Three dimensional tracking of particles and their local orientations

In this paper, digital stereoscopic imaging and reconstruction techniques have been developed for the tracking and velocity measurement of solid particles using a single camera. The variable shutter speeds of a digital camera are used to control the trajectory length of the tracked particles. A colour coding method has been developed to resolve the ambiguity of particle flow direction and avoid the confusion in manually matching particle pairs. The method could be applied to validate the automated particle matching algorithms. Besides using points (particle centroids) a matching algorithm for a stereo reconstruction pixel to pixel matching algorithm has been applied. The latter is able to resolve not only the particle position but also the shape and orientation of a non-spherical particle. This is of importance since non-spherical particle or bubble geometry is common in a practical system and the non-spherical geometry has a strong effect on the particle or bubble dynamics. The potential of using this system for the quantitative 3D measurement of multiphase flow has been demonstrated with several test cases.     

SiCp增强铝基复合材料与芳纶纤维增强摩擦材料摩擦副摩擦学特性与模型研究

对 Si Cp含量为 2 0 % (vol% )的铝基复合材料和芳纶纤维增强摩擦材料组成的摩擦副在干摩擦条件下的摩擦学特性进行了试验研究。试验表明 :摩擦副的摩擦系数受 Kevlar增强摩擦材料的热分解温度所控制 ,当温度低于2 0 0℃时 ,摩擦系数随滑动速度和温度增大而增大 ,并处于较高水平 ;当温度高于 2 0 0℃时 ,摩擦材料发生热分解 ,摩擦系数急剧下降到较低水平。摩擦材料具有磨损量和磨损率随滑动速度增加而减小的明显特征 ,摩擦副具有良好的耐磨性。建立了描述该摩擦副摩擦特性的数学模型。并用其解释了实验中的摩擦学现象。     

A parametric investigation of arc spraying process for rapid mould making

Arc spraying has recently found its application in rapid mould making and is used predominantly as a technique for the production of the mould crust. In this paper, the influence of the spraying parameters, i.e. air pressure, loading voltage, wire feed rate, spraying distance and gun transverse velocity, on the resulting crust qualities such as the surface finish and bond strength, was investigated. Since the crust is built layer upon layer by the deposition of metal particles, particle morphology was found to play a key role in the resulting crust qualities. It was found that the particle morphology varies with the spraying parametric settings and their relationships were studied by using a Taguchi experimental technique. The results also show that air pressure is the prevailing parameter, followed by loading voltage, in determining the metal particle size, and that small particles with high deposition density lead to better bond strength. In addition, there is evidence showing that the combined effects of the particle morphology, particle impact force and particle temperature determine the resulting surface finish of the crust.     

Improving the Delaunay tessellation particle tracking algorithm in the three-dimensional field

Particle tracking velocimetry (PTV) algorithms match particles across two consecutive frames corresponding to a certain flow pattern. PTV based on Delaunay tessellation (DT-PTV) has a succinct structure and depends minimally on algorithmic assumptions. This study proposes several methods for improving DT-PTV performance in the three-dimensional field. The improved version, called 3DT-PTV, is tested using synthetic flows with various parameters and under difficult circumstances. Results show that 3DT-PTV performs better than the classical version in addressing flows with a noticeable ratio of particles without match and those with an excessive ratio of the inter-frame particle displacement to the inter-particle distance.     

Study of the parametric dependence of erosion wear for the parallel flow of solid–liquid mixtures

The phenomenon of erosion wear due to the cutting action of solid particles in solid–liquid mixture flows has been studied in a slurry pot tester. Special fixtures and design modifications were incorporated in a slurry pot tester in order to ensure that the erosive wear on the wear piece is primarily due to parallel flow of the mixture. Experiments performed at various solid concentrations, particle sizes and velocities, show that the parallel flow wear increases with increase in solid concentration, particle size and velocity. The parametric dependence on velocity is comparatively much stronger as compared to that on either solid concentration or particle size.     

Measurements of three-dimensional velocities of spray droplets using the holographic velocimetry system

The Holographic Particle Velocimetry system can be a promising optical tool for the measurements of three dimensional particle velocities. In this study, the holographic particle velocimetry system was used to measure the sizes and velocities of droplets produced by a commercial full cone spray nozzle. As a preliminary validation experiment, the velocities of glass beads on a rotating disk were measured with uncertainty analysis to identify the sources of all relevant errors and to evaluate their magnitude. The error of the particle velocity measured by the holographic method was 0.75 m/s, which was 4.5% of the known velocity estimated by the rotating speed of disk. The spray droplet velocities ranged from 10.3 to 13.3 m/s with average uncertainty of +-1.6 m/s, which was +-14% of the mean droplet velocity. Compared with relatively small uncertainty of velocity components in the normal direction to the optical axis, uncertainty of the optical axis component was very high. This is due to the long depth of field of droplet images in the optical axis, which is inherent feature of holographic system using forward-scattering object wave of particles.     

基于维诺图匹配的粒子跟踪测速法

针对密集颗粒流速度场分布的测量问题,提出了基于维诺图匹配的粒子跟踪测速法。首先,通过对图像粒子进行维诺图构建,给出面积相似度筛选匹配粒子的条件;其次,引入Delaunay三角网搜索结构,通过计算维诺多边形的形状相似度来匹配粒子;再次,研究了去除错误匹配粒子矢量的方法和匹配算法中的关键参数;最后,通过模拟二维旋转流场运动以及二维转盘中的颗粒流实验对算法进行了测试。结果表明:维诺图匹配的匹配准确率高于DT-PTV并且在处理密集粒子匹配效果上更好;维诺图匹配算法适用于测量密集颗粒流速度场分布,颗粒匹配准确率高达99%,并由得到的颗粒流速度场分布验证了算法的有效性。     

Processing parameters affecting cold spay coatings performances

In the present paper, the microstructural and mechanical properties of metal–metal cold spray deposits are described. Different spray particles coatings (Al-, Ti-, Ni-based particles) deposited on different substrates (Al-, Ti-, Fe-, Ni-, Mg-based bulk materials) were produced and their mechanical and microstructural properties were characterized. Microhardness, porosity, grain size and adhesion strength of the coatings were analyzed as a function of processing parameters such as particle velocity, particle dimensions, gas density, substrate hardness, and temperature. The results were employed to build a database used to obtain a provisional model through a multi-objective optimization software. For each different substrate and particle type, the working points were defined in terms of processing parameters to optimize mechanical and microstructural behavior of coatings. The error calculation of the final properties of the deposits demonstrated the precision of the developed model.     

砂粒粒径对航空涡轴发动机压气机叶片冲蚀磨损的影响研究

高原、沙漠和沿海等服役环境中不同粒径的砂粒不可避免地对涡轴发动机压气机叶片造成冲蚀磨损,破坏叶片叶型和动力学特性,严重危及涡轴发动机使用寿命和直升机飞行安全。基于Finnie冲蚀磨损理论推导了颗粒对金属表面的磨损率表达式,分析颗粒粒径对材料冲蚀磨损率的影响,以某型涡轴发动机压气机动叶和静叶为研究对象,设计搭建砂粒冲击速度测试装置和钛合金冲蚀磨损实验装置,通过典型砂粒粒径下冲蚀磨损实验获取磨损率表达式中与靶材材料和冲击速度相关的关键参数,结合气固两相流动力学分析开展砂粒粒径对压气机动叶和静叶冲蚀磨损的影响研究。结果表明：砂粒粒径与冲击速度存在内在关联,材料冲蚀磨损率与砂粒冲击速度呈幂函数关系。实验条件下,砂粒粒径由177 μm增至423 μm时,其冲击速度平均降低约17%。压气机动叶和静叶的磨损集中区域不随砂粒粒径的改变而变化,但磨损程度差异明显,其中177 μm砂粒对动叶和静叶造成的最大冲蚀磨损率浓度值相比423μm砂粒分别增加91%和131%。研究结果为涡轴发动机压气机叶片抗磨损设计提供了理论参考。