关 键 词：

机械类毕业论文中英文对照文献翻译 机械类 毕业论文 中英文 对照 文献 翻译 计算 流体 分析 磨料 水射流 切割

资源描述：

【机械类毕业论文中英文对照文献翻译】计算流体分析磨料水射流切割头,机械类毕业论文中英文对照文献翻译,机械类,毕业论文,中英文,对照,文献,翻译,计算,流体,分析,磨料,水射流,切割

内容简介：

计算流体分析磨料水射流切割头文摘水射流切割是在一定范围内不受热的条件来切割厚金属的技术。介绍了流体动力学(CFD)和理论分析优化混合多相零组件方法。水,空气,是组成混合研的磨腔。此模型是用来预测研磨和空气的影响和混合在混合管内的不同距离的影响。与此同时,粒子在喷嘴腔跟踪并进行监控气蚀磨蚀速率的密度。结果表明,喷管长度作用于混合水、空气成分等,磨料水射流的速度气蚀磨蚀速率的影响主要在喷嘴腔上。k-的湍流模型进行仿真研究的磨料加上空气。该调查显示,受侵蚀强度较高,喷嘴身体的初始区长度越长,当喷嘴的长度增加,体积空气相应增大。口的入口处受到高压送水小溪(以最小限度的微粒计算),并导致成切削领域的先锋。为了减少在混合室乱流可使用真空协助,但应当采取防御措施,因为没有不经过混合室的。关键词：AWJ;CFD;侵蚀;多相混合1引言AWJ(磨料射流加工是一种用途广泛的几乎所有的材料都能被切割,并且可以合理的完成加工表面。特点在极其低的切削力,可以忽略热效应。这焦点试管水射流切割系统加速了磨料粒子用于割磨料射流速度越快越好射出。磨料射流是由两个连续的阶段和固体颗粒相连的组成,这使得它们waterjets复杂性远大于以往。速度分布是一个非常重要的参数在精度磨料射流切割中。在水射流中可更换水射流切割头集中管,它可以使研磨粉剂充分与水和空气混合。因为较高的速度和剪切应力发生在聚焦管壁、并发生侵蚀。因此,喷射的连贯性下降和聚焦管的直径提高了,这些不需要的精密切割。不像其他流体力学,水在AWJ高压下可被压缩成流体。磨料水射流速度可在帕努力动力平衡和在压缩因子等条件下进行计算。可测量侵蚀聚焦管,这是对先前进行的实验否认。由于磨损侵蚀是一个复杂功能并影响粒子作用和粒子壁的性质。进行了模拟,以确定特点在切削材料的侵蚀,不同颗粒角度。土壤侵蚀模型提供Finnie45的一种确定材料切除或侵蚀率密度。Ansys采用CFX 11适用于计算流体力学(CFD仿真,在那里进行了调查空气和磨料射流速度,以及流失以不同管的流量磨料及形状系数的研磨粉剂。2理论2.1理论水射流速度 (1)水压缩 (2) 水射流方程 (3)当L=300Mpa 和n=0.1368在25度压缩条件 (4)这可压缩性系数因子和排放可以用来表达水射流速度 (5)2.2侵蚀模型几乎在所有金属、侵蚀发现不同的角度根据转角和角速度关系E=K (6)当E=无穷小量V=颗粒碰撞速度。n=2f=影响无穷量的因数在Ansys子域E= (7)当V0=侵蚀速率= E*N* (8)当N=计入重量率 m=粒子重量因此在腔中颗粒发生侵蚀，气蚀会在侵蚀区管壁聚集并且磨蚀速率密度(公斤/ s /平方米)。 空气和磨料耦合在一起、两种类型的耦合都会被用,也就是说、单耦合的和完全耦合关系。 单向耦合是简单的预测粒子的路径基于流场，因此都是不同的方式不去影响连续相流动。 完全耦合粒子交换,并且是连续的阶段,允许连续流和粒子相互影响。形状因子研磨粉剂是很重要参数。一个圆形的粒子有最大的形状系数为1.0;不规则的颗粒和它的形状等因数有关探讨了研磨颗粒侵蚀研究对象可改变其形状因子。3主要参数几何和参数采用CFD数值模拟的方法对三维截割头的模型革新设计而成,并采用CFD软件用于啮合。所有必要的边界条件应用于Ansys采用CFX 11。表1显示的几何参数及边界条件 数值模拟计算结果。 在对称模型、计算 在短时间内是用的网格总数减呢比完美的模型。 只要有可能,采用CFX运用有限元分析软件Ansys,建议采用对称。表1.1几何和边界参数。几何/ 边界条件 参数几何由毫米直径孔, 流量系数、Cd = 0.8混合室直径4.2毫米,3毫米长度是混合室 管直径= 1.5毫米焦点 焦点的全长= 70毫米 磨料入口直径= 1.56 mm边界磨料流量= 8、20、30克/秒 磨料密度= 7854公斤/方 磨料形状系数= 1,0.9,0.7 空气流速= 5米/秒 水的压力= 470兆帕 水=密度1134公斤/方 图1.1 边界条件的截割头应用4 实验主要的仿真结果进行了比较定理和先前的试验由不同的研究者。 这是且报方针是一个准求的调查射流速度来衡量7。 这测量,高速照相机被用来观察的喷射的时间和距离。 除了柯达SR-Series运动分析仪、水射流机组合成顶部有限公司用于这个实验。相机就会帧率记录时间和对峙将决定的距离。 如果喷射的速度不变,考虑到高速喷射和非常小的相隔距离60毫米,然后它可用来测量速度达600米/秒喷射框架 率10000 fps。 这是可能的射流速度计算把距离的计算出的时 要求的帧,需要经历的距离。 实验考虑,并根据参数条件采用模拟技术。5. 结果和讨论从式(1)、(3)和(4), = 970米/秒； = 934米/秒；=0.96考虑流量和压缩性系数。从式(5)，=,0.8x0.96x970=745米/秒水的最大速度确定的CFD分析是735米/秒的出口,孔,如图2.与空气混合后,磨料水射流速度发现。表2. 速度和最大侵蚀变化为不同的质量流量的模具质量流率(g /秒) 马克斯侵蚀(公斤/ s / m2) 速度X108 磨料(米/秒)80.96295202.144290303.62287在聚焦管出局384米/秒,而钢速度被发现300米/秒的单程耦合有空气。由于流量变化的研磨粉剂。 产品的速度保持不变。 然而,为充分结合空气。最大速度水射流在喷管出口多种多样,以及增加的质量流率速度减水已经加速的更多的颗粒。 表2所示的变化规律磨料(180微米)和侵蚀在腔壁停留了充分的耦合关系磨料。研磨粉剂在加速聚焦管,因此,速度增加聚焦的长度 管。 因此,聚焦管的长度是至关重要的在水射流的优化过程中。磨料水、空气等,在混合腔创建一个非常复杂的状态。 试图是8 可以观看混合,重新制造了水道air-abrasive频道,玻璃材料。 结果 此举表明,占据了vortex-type流动流型吸区。 目前的CFD仿真 显示涡流创造了在混合室。 从的动画气流线、涡流现象提供了最初的机制,磨料诱导作用”。 图4阐述了混合腔里面涡创造被水(黄色),空气（彩虹),研磨剂(红色)。 M.鲍威尔9解释说,动能和动力 从高压水传送给研磨颗粒。 应用动能沿颗粒锐利的边缘。 因此,形状因素起到影响磨料速度。在应用了在磨的形状因数粒子分析、磨料射流速度增高。 形状因数0.9和粒径100微米的,磨料速度309.5米/秒),及305米的单向性和fully-coupled模型，另外尽量减少平均直径并且粒子高速率应用与形状因数都是不规则的形状颗粒会产生出更好的表面切割标本。图2.显示的速度增加同一种磨料的内部集中管。 图3.混合水 空气 磨料图4浇流孔液压翻转,流动分离,或空10所聚集的发生刃口锋利的孔在高压力。 图5显示液压翻转和临界区孔负责加速水。 根据M .鲍威尔、如果水含有中止颗粒，切削能发生在空的入口处。M . Nanduri喷嘴磨损了应用三种类型的调查和发散穿类型。 短距离入口聚焦管、穿过是最大值。我们的CFD仿真结果表明相同的方式的侵蚀。在图6,类似于实验结果,磨损率沿长度密度降低聚焦管。确定形状影响因素对侵蚀管的影响、0.7和0.9形状系数,同时保持大量的质子流量号8点是为100微米的粒子大小。 结果产生了一个更高的气蚀磨蚀速率密度的形状因素比形状0.7比起形状0.9的形状。 这意味着如果循环磨料粒子是使用,那将会下降导致加工效率。然而,在生活聚焦管将会增加。相反的是事实形状不规则的对这些情况研磨颗粒有影响。 表3显示在速度和变化侵蚀的单程耦合情况形状因素的变化以不变的质量流率8克/秒想像被侵蚀质量的流率都可分为完全耦合的单向性和耦合模型,完成了之间空气和磨料作为单向耦合元件不能分享彼此的态势,侵蚀成了线性的,然而粒子,完全耦合非线性和侵蚀作用具有较高的价值。 图7显示质量流量的影响上了侵蚀聚焦管壁。 第一个如图3局的传播。7高速水射流。1000fps,时间的差距 两局是1/10000 s。 为470兆帕压力,要求时间还不到2/10000 s,这表明速度还不到400米/秒。 模拟水射流切割速度是384米/秒,因此,模拟和实验吗结果非常接近。表3 形状因素的影响对速度的磨具和最大的管壁集中流失麦克斯侵蚀形状因素(公斤/ s / m2) 速度X10 磨料(米/秒)1299.90.960.93051.450.7309.52.48图5. 管壁集中流失图6.测量的水射流速度6. 结论 仿真结果表明,聚焦的长度管是由加快研磨粉剂和那磨损量上提高集中管壁颗粒形状的变化因素。 如果质量流率研磨粒非常高,那么喷射的效率将会减少“水射流增强流颗粒。 高速湍流射流发生联系与一个相对低速气流,因此,漩涡创造了在混合腔作用于混合不同的阶段。 量流线形的磨具粒子取决于混合室的形状。 目前,搅拌缸通常为圆柱形的形状。需要进一步的调查,想像混合循环、椭圆-,和hyperbolic-shaped混合的房间, 就能指导的流线形射流在相比在控制呼气圆柱腔中。 Journal of Mechanical Science and Technology 24 (2010) 249252 /content/1738-494x DOI 10.1007/s12206-009-1142-5 Computational fluid analysis of abrasive waterjet cutting head Md. G. Mostofa1,*, Kwak Yong Kil1 and Ahn Jung Hwan2 1Department of Mechanical and Intelligence System Engineering, Pusan National University, Busan, Korea 2School of Mechanical Engineering, Pusan National University and ERC/NSDM, Busan, Korea. (Manuscript Received May 2, 2009; Revised September 28, 2009; Accepted October 16, 2009) - Abstract Waterjet cutting is an appealing technology for cutting thick materials with zones that must not be affected by heat. This paper presents computational fluid dynamics (CFD) and theoretical analyses to optimize the mixing of components by the multi-phase approach. Water, air, and abrasives are mixed in a mixing chamber. This modeling is used to predict the influence of air and abrasives on the mixing at different distances within the mixing tube. At the same time, particle tracking was conducted to monitor the erosion rate density at the nozzle wall. Results show that nozzle length has an effect on the mixing of water, air, and the abrasives, and that the velocity of the wa-terjet influences the erosion rate at the nozzle wall. The k- turbulence model was used for simulation of the abrasive coupled with air. This investigation reveals that the erosion in the nozzle body is higher at the initial zone and that as the length of the nozzle length in-creases, the volume fraction of air increases accordingly. The entrance of the orifice is affected by a highly pressurized water stream (with minimal particulate matter), which causes chipping at the leading edge. To reduce the turbulence inside the mixing chamber, the use of a vacuum assist could be helpful, but precautions should be taken in order that the abrasives do not escape from the mixing cham-ber. Keywords: AWJ; CFD; Erosion; Multiphase mixing - 1. Introduction Abrasive waterjet (AWJ) machining is a versatile process capable of cutting almost any material, with a reasonable fin-ish on the machined surface. Its characteristics include ex-tremely low cutting force and negligible thermal effects. The focus tube in a waterjet cutting system accelerates the abrasive particles used for cutting. The faster the abrasive jets, the bet-ter the performance. Abrasive jets are made up of two con-tinuous phases and a solid particle phase, which makes them much more complex than plain waterjets. The velocity distri-bution is a crucial parameter in abrasive waterjet precision cutting. The most replaceable part in a waterjet cutting head is the focusing tube, which helps the abrasive particles to mix with water and air. Due to high velocity and shear stress de-veloped on the focusing tube wall, erosion occurs. As a result, jet coherence decreases and the diameter of the focusing tube increases, which are undesirable in precision cutting 1. Unlike problems encountered in the other fluid dynamics, water is compressible in AWJ under high pressure. Abrasive waterjet velocity was calculated 2 from the momentum bal-ance of Bernoullis equation and the compressibility factor. To measure the erosion of the focusing tube, a destructive 3 experiment was previously conducted. The wear of a wall due to the erosive effect of particle impact is a complex function of particle impact, particles, and wall properties. A simulation was conducted to determine the characteristics of erosion in cutting materials for different particle angles. The erosion model of Finnie 4 provided 5 a way to determine the material removal or erosion rate density. Ansys CFX 11.0 was used for the computational fluid dynamics (CFD) simulation, where investigation was done on the waterjet air and abrasive velocity, as well as the erosion in the focusing tube by varying the mass flow rate of the abrasive and shape factor of the abrasive particles. 2. Theory 2.1 Theoretical waterjet velocity 2thpV= (1) Compressibility of water 1nPL=+ (2) The resulting equation of the waterjet is This paper was presented at the ICMDT 2009, Jeju, Korea, June 2009. This paperwas recommended for publication in revised form by Guest Editors Sung-Lim Ko, Keiichi Watanuki. *Corresponding author. Tel.: +82 51 510 3087, Fax.: +82 51 581 3087 E-mail address: mostofa_01buet KSME & Springer 2010 250 M. G. Mostofa et al. / Journal of Mechanical Science and Technology 24 (2010) 249252 10211(1)njLPVnL=+ (3) where L= 300 MPa and n= 0.1368 at 25 C Compressibility factor 111(1)njthVLPVPnL=+ (4) This compressibility factor and the coefficient of discharge can be used to express waterjet velocity jdth V = CV (5) 2.2 Erosion model For nearly all metals, erosion is found to vary with impact angle and velocity according to the relationship nE=kVf()p (6) where E= dimensionless mass Vp= particle impact velocity, n=2 ( )f = dimensionless function of impact. Implementation in Ansys CFX npoVE =( )Vf x (7) where 01V =nk Erosion rate =pE*m(kg/s) (8) where =number rate, mp=mass of particle. The overall erosion of the wall is therefore the sum over all particles. Erosion rate density (kg/s/m2) will provide the erosion zone of the focusing tube wall. For coupling air and abrasive, two types of coupling were used, namely, one-way coupled and fully coupled. One-way coupling simply predicts the particle paths based on the flow field, and, therefore, does not influence the continuous phase flow. Fully coupled particles exchange momentum with the continuous phase, allowing the continuous flow to affect the particles, and the particles to affect the continuous flow. Shape factor is an important parameter for abrasive particles. A circular particle has a maximum shape factor of 1.0; the more irregular the particle is, the lower its shape factor. Erosion was investigated by changing the shape factor of abrasive particles. 3. Geometry and parameters For the CFD simulation, a 3-D model of the cutting head was designed and ICEM CFD software was used for meshing. All the necessary boundary conditions were applied in Ansys CFX 11.0. Table 1 shows the geometrical and boundary conditions for the CFD analysis. In the symmetrical model, the computation was made in less time as the total number of mesh decreased compared to the full model. Whenever possible, Ansys CFX suggests applying symmetry. Table 1. Geometrical and boundary parameters. Geometry/ boundary conditions Parameters Geometry Orifice diameter=0.96 mm Coefficient of discharge, Cd=0.8 Mixing chamber diameter=4.2 mm Mixing chamber length=3 mm Focus tube diameter=1.5 mm Focus tube length=70 mm Abrasive inlet diameter=1.56 mm Boundary conditions Abrasive mass flow rate= 8, 20, 30 g/s Abrasive density=7854 kg/m3 Abrasive shape factor=1, 0.9, 0.7 Air velocity=5 m/s Water pressure=470 MPa Density of water=1134 kg/m3 V0=1.0 m/s Fluid solid coupling= One-way coupled and fully coupled Fig. 1. Boundary conditions applied to the cutting head. 4. Experiment Major simulation results were compared with theorem and the previous experiments performed by different scholars. The performed to ensure that the simulation 6 was an accurate investigation to measure the jet velocity 7. For this meas-urement, a high-speed camera was used to observe the jet travel time and distance. In addition to the KODAK SR-Series motion analyzer, waterjet machine form TOPS CO., LTD was used for this experiment. The set frame rate of the camera will record the time and the standoff will determine the distance. If the velocity of the jet remains constant, considering the high-speed jet and very small standoff distance of 60 mm, then it is possible to measure the velocity up to 600 m/s jet for frame rate 10000 fps. It is possible to calculate the jet velocity by dividing the standoff distance by the time calculated from the required frames that are needed to travel the distance. Experi-mental parameters were considered according to the boundary conditions applied during the simulations. 5. Results and discussion From Eqs. (1), (3), and (4), Vth= 970 m/s; Vj=934 m/s; =0.96 Considering the coefficient of discharge and compressibility from Eq. (5), Vj = 0.8X0.96X 970= 745 m/s The maximum velocity of water determined in the CFD analysis was 735 m/s at the orifice exit, as shown in Fig. 2. After mixing with air and abrasive, the waterjet velocity found M. G. Mostofa et al. / Journal of Mechanical Science and Technology 24 (2010) 249252 251 Table 2. Variation velocity and maximum erosion for different mass flow rate of abrasive. Mass Flow rate (g/s) Max Erosion (Kg/s/m2)X108 Velocity of abrasive (m/s)8 0.96 295 20 2.414 290 30 3.62 287 Length vs Waterjet Velocity010020030040050060070080000.020.040.060.080.1Length(m)Waterjet Velocity(m/s)Waterjet Velocity Fig. 2. Waterjet velocity variations along the cutting head. at the focusing tube exit was 384 m/s, whereas the steel veloc-ity was found to be 300 m/s for one-way coupling with air. Due to the change in the mass flow rate of the abrasive parti-cles, the velocity of the abrasives remained unchanged. How-ever, for fully coupled with air, the maximum velocity of the waterjet at the nozzle exit varied, and with the increase in mass flow rate the velocity decreased as the water had to ac-celerate more particles. Table 2 shows the variation of the abrasive (180 microns) and erosion on the wall for fully cou-pled abrasive. Abrasive particles are accelerated inside the focusing tube, therefore, the velocity increases with the length of the focus-ing tube. Thus, the length of the focusing tube is crucial in the optimization of the waterjet. Fig. 3 shows the velocity incre-ment of the abrasive inside the focusing tube. The turbulence of water, air, and abrasives inside the mix-ing chamber create a very complex state. An attempt 8 was made to visualize the mixing by recreating the water channel and air-abrasive channel with Plexiglas material. Results of that attempt showed that the vortex-type flow dominates the flow pattern in the suction zone. The present CFD simulation shows the vortex created inside the mixing chamber. From the animation of the air stream line, the vortex phenomenon pro-vides the initial mechanism of abrasive entrainment. Figure 4 illustrates the vortex created inside the mixing chamber by water (yellow), Air (rainbow), and abrasives (red). M. Powell 9 explained that the kinetic energy and momen-tum are transferred from the high-pressure water beam to the abrasive particles. The kinetic energy is applied along the sharp edges of the particles. Therefore, the shape factor has an effect on abrasive velocity. After applying the shape factor in the abrasive particle analysis, the abrasive velocity increased in the waterjet. For a shape factor of 0.9 and particle size of 100 micron, abrasive velocity were 309.5 m/s and 305 m/s for the one-way and fully-coupled models, respectively. Despite the reduction in the mean diameter, the particle velocity was higher when the Fig. 3. Acceleration of abrasive along focusing tube. Fig. 4. Mixing of water, air and abrasive. Fig. 5. Flow around orifice. shape factor was applied, which indicates that using irregular shape particles will produce a better surface in the cutting specimen. Hydraulic flips, flow separation, or cavitations 10 occur with a sharp edge orifice at high pressure. Figure 5 shows the hydraulic flip and critical zone of the orifice responsible for accelerating water. According to M. Powell, chipping could occur at the entrance of the orifice if water contains suspended particles. M. Nanduri investigated nozzle wear by applying three types of investigations and divergent wear types. At a short distance from the focusing tube, entrance wear was at maxi-mum. Our CFD simulation shows the same manner of erosion. In Fig. 6, similar to the experimental results, the erosion rate density decreases along the length of the focusing tube. To determine the effect of shape factor on erosion of the fo-cusing tube, 0.7 and 0.9 shape factor were applied while keep-ing the mass flow rate constant at 8 g/s for 100 micron particle size. Results yielded a higher erosion rate density for shape factor 0.7 than for shape 0.9. This means that if circular abra-sive particles are used, then the cutting efficiency will de-crease; however, the life of the focusing tube will increase. The opposite will be true for the case of irregularly shaped abrasive particles. Table 3 shows the variation in velocity and erosion for one-way coupling case for variation of shape fac-tor with a constant mass flow rate of 8 g/s. To visualize the effect of mass flow rate on erosion for both 252 M. G. Mostofa et al. / Journal of Mechanical Science and Technology 24 (2010) 249252 Table 3. Effect of shape factor on the velocity of abrasive and maxi-mum erosion on the focusing tube wall. Shape factor Max Erosion (Kg/s/m2)X108 Velocity of Abrasive (m/s)1 .96 299.9 0.9 1.45 305 0.7 2.48 309.5 Fig. 6. Erosion on the focusing tube wall. Mass Flow Rate vs Erosion Rate Density00.511.522.533.54010203040Mass Flow Rate(g/s)Erosion Rate Density(Kg/s/m2)X108Fully CoupledOne Way Coupled Fig. 7. Effect of mass flow on the erosion of focusing tube wall. Fig. 8. Measurement of the waterjet velocity. one-way and fully coupled models, coupling was done be-tween air and abrasive. As one-way components coupling do not share each others momentum, the erosion became linear, whereas, for fully coupled particles, erosion is nonlinear and has higher value. Fig. 7 shows the effect of mass flow on the erosion of the focusing tube wall. The first three frames shown in Fig. 7 are the propagation of a high-speed waterjet. For 10000 fps, the time gap between two frames was 1/10000 s. For 470 MPa pressure, the required time was less than 2/10000 s, which indicates that the velocity was less than 400 m/s. Simulated velocity of the waterjet cut-ting was 384 m/s, therefore, the simulation and experimental results were very close. 6. Conclusion The simulation results show that the length of the focusing tube is responsible for accelerating the abrasive particles, and that the erosion rate increases on the focusing tube wall with the change in the particle shape factor. If the mass flow rate of the abrasive is very high, then the efficiency of a jet could decrease as the thin waterjet stream has to accelerate more particles. The high-speed turbulent waterjet comes in contact with a relatively low-speed air stream, thus, a vortex will be created inside the mixing chamber, which has an effect on the mixing of different phases. The stream line vector for abrasive particles depends on the shape of the mixing chamber. Cur-rently, the mixing cylinder is generally cylindrical in shape. Further investigation is needed to visualize the mixing for circular-, elliptical-, and hyperbolic-shaped mixing chambers, as they are able t