Abrasive water jet cutting technology is widely applied in the materials processing today and attracts great attention from scholars, but many phenomena concerned are not well understood, especially in the internal je...Abrasive water jet cutting technology is widely applied in the materials processing today and attracts great attention from scholars, but many phenomena concerned are not well understood, especially in the internal jet flow of the cutting head at the condition of ultra-high pressure. The multiphase flow in the cutting head is numerically simulated to study the abrasive motion mechanism and wear inside the cutting head at the pressure beyond 300 MPa. Visible predictions of the particles trajectories and wear rate in the cutting head are presented. The influences of the abrasive physical properties, size of the jewel orifice and the operating pressure on the trajectories are discussed. Based on the simulation, a wear experiment is carried out under the corresponding pressures. The simulation and experimental results show that the flow in the mixing chamber is composed of the jet core zone and the disturbance zone, both affect the particles trajectories. The mixing efficiency drops with the increase of the abrasive granularity. The abrasive density determines the response of particles to the effects of different flow zones, the abrasive with medium density gives the best general performance. Increasing the operating pressure or using the jewel with a smaller orifice improves the coherency of p articles trajectories but increases the wear rate of the jewel holder at the same time. Walls of the jewel holder, the entrance of the mixing chamber and the convergence part of the mixing tube are subject to wear out. The computational and experimental results give a qualitative consistency which proves that this numerical method can provide a reliable and visible cognition of the flow characteristics of ultra-high pressure abrasive water jet. The investigation is benefit for improving the machining properties of water jet cutting systems and the optimization design of the cutting head.展开更多
The objectives of the work were to study the effect of drip irrigation circuits (DIC) and lateral lines lengths (LLL) on: Flow velocity (FV) and velocity head (VH). Laboratory tests were conducted at Irrigation Device...The objectives of the work were to study the effect of drip irrigation circuits (DIC) and lateral lines lengths (LLL) on: Flow velocity (FV) and velocity head (VH). Laboratory tests were conducted at Irrigation Devices and Equipments Tests Laboratory, Agricultural Engineering Research Institute, Agriculture Research Center, Giza, Egypt. The experimental design of laboratory experiments was split in randomized complete block design with three replicates. Laboratory tests carried out on three irrigation lateral lines 40, 60, 80 m (LLL1, LLL2;LLL3) under the following three drip irrigation circuits (DIC): a) one manifold for lateral lines or closed circuits with one manifold of drip irrigation system (CM1DIS);b) closed circuits with two manifolds for lateral lines (CM2DIS), and c) traditional drip irrigation system (TDIS) as a control. Concerning FV values, DIC and LLL treatments could state in the following ascending orders: TDIS 1DIS 2DIS and LLL1 2 3, respectively. FV varied from 0.593 m·sec–1 to 1.376 m?sec–1. i.e FV –1 and this is necessary to avoid the effect of water hammer in the main and sub-main lines, but in lateral line, it can cause silt and clay precipitation problems. The differences in FV among DIC and LLL were significant at the 1% level. The effect of interaction: DIC X LLL on FV values, were significant at the 1% level. The maximum and minimum values of FV were noticed in these interactions: CM2DIS X LLL3 and TDIS X LLL1, respectively. The following ascending orders TDIS 1DIS 2DIS and LLL1 2 3 expressed their effects on VH respectively. Differences in VH among DIC and/or LLL were significant at the 1% with few exceptions. The effects of interactions: DIC X LLL on VH were significant at the 1% level in some cases. The maximum and minimum values of VH were found in the interactions: CM2DIS X LLL3 and TDIS X LLL1, respectively.展开更多
应用Solid Works Flow Simulation软件对1款乳化头的4个不同定子结构进行了CFD(计算流体力学)分析,通过仿真计算,直观获得了釜内不同乳化头周围的流体速度分布云图和流线轨迹;通过粒子示踪法模拟了制胶物料在乳化头作用下的分布状态;最...应用Solid Works Flow Simulation软件对1款乳化头的4个不同定子结构进行了CFD(计算流体力学)分析,通过仿真计算,直观获得了釜内不同乳化头周围的流体速度分布云图和流线轨迹;通过粒子示踪法模拟了制胶物料在乳化头作用下的分布状态;最后在定子外围设定草绘面,并获取该面上的平均速度,以定量预测和对比不用定子结构的乳化效果。研究结果表明:通过CFD分析,可从4个方案中选择最佳结构的定子,从而达到优化定子的目的;在4个定子结构中,无顶梢且上宽下窄型出料口的定子具有相对最好的分散效果。展开更多
跨介质航行体入水瞬间会受到巨大的冲击载荷,极易导致结构破坏甚至内部器件失灵。为发展有效的降载方法,本文基于VOF(Volume of Fluid)多相流模型,研究头部喷气航行体入水过程的载荷特性和流体动力特性,分析喷气压力、喷气高度对降载效...跨介质航行体入水瞬间会受到巨大的冲击载荷,极易导致结构破坏甚至内部器件失灵。为发展有效的降载方法,本文基于VOF(Volume of Fluid)多相流模型,研究头部喷气航行体入水过程的载荷特性和流体动力特性,分析喷气压力、喷气高度对降载效果的影响,并探索头部喷气降载方法有效性的入水速度范围。研究结果表明,头部喷气使自由液面下凹形成空腔,并能极大地降低航行体所受阻力和冲击力,延缓了航行体撞水时间,从而实现冲击载荷控制;喷气压力和喷气高度对入水空泡形态及冲击压力峰值的影响都不大,合理的选择既能达到降载效果又能节约喷气量;入水速度为50 m/s时,降载量高达76.51%,但当入水速度为300 m/s时,降载量仅为39.92%。因此,针对高亚声速跨介质入水问题,需进一步探索主被动相结合的复合降载方法。展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50806031)
文摘Abrasive water jet cutting technology is widely applied in the materials processing today and attracts great attention from scholars, but many phenomena concerned are not well understood, especially in the internal jet flow of the cutting head at the condition of ultra-high pressure. The multiphase flow in the cutting head is numerically simulated to study the abrasive motion mechanism and wear inside the cutting head at the pressure beyond 300 MPa. Visible predictions of the particles trajectories and wear rate in the cutting head are presented. The influences of the abrasive physical properties, size of the jewel orifice and the operating pressure on the trajectories are discussed. Based on the simulation, a wear experiment is carried out under the corresponding pressures. The simulation and experimental results show that the flow in the mixing chamber is composed of the jet core zone and the disturbance zone, both affect the particles trajectories. The mixing efficiency drops with the increase of the abrasive granularity. The abrasive density determines the response of particles to the effects of different flow zones, the abrasive with medium density gives the best general performance. Increasing the operating pressure or using the jewel with a smaller orifice improves the coherency of p articles trajectories but increases the wear rate of the jewel holder at the same time. Walls of the jewel holder, the entrance of the mixing chamber and the convergence part of the mixing tube are subject to wear out. The computational and experimental results give a qualitative consistency which proves that this numerical method can provide a reliable and visible cognition of the flow characteristics of ultra-high pressure abrasive water jet. The investigation is benefit for improving the machining properties of water jet cutting systems and the optimization design of the cutting head.
文摘The objectives of the work were to study the effect of drip irrigation circuits (DIC) and lateral lines lengths (LLL) on: Flow velocity (FV) and velocity head (VH). Laboratory tests were conducted at Irrigation Devices and Equipments Tests Laboratory, Agricultural Engineering Research Institute, Agriculture Research Center, Giza, Egypt. The experimental design of laboratory experiments was split in randomized complete block design with three replicates. Laboratory tests carried out on three irrigation lateral lines 40, 60, 80 m (LLL1, LLL2;LLL3) under the following three drip irrigation circuits (DIC): a) one manifold for lateral lines or closed circuits with one manifold of drip irrigation system (CM1DIS);b) closed circuits with two manifolds for lateral lines (CM2DIS), and c) traditional drip irrigation system (TDIS) as a control. Concerning FV values, DIC and LLL treatments could state in the following ascending orders: TDIS 1DIS 2DIS and LLL1 2 3, respectively. FV varied from 0.593 m·sec–1 to 1.376 m?sec–1. i.e FV –1 and this is necessary to avoid the effect of water hammer in the main and sub-main lines, but in lateral line, it can cause silt and clay precipitation problems. The differences in FV among DIC and LLL were significant at the 1% level. The effect of interaction: DIC X LLL on FV values, were significant at the 1% level. The maximum and minimum values of FV were noticed in these interactions: CM2DIS X LLL3 and TDIS X LLL1, respectively. The following ascending orders TDIS 1DIS 2DIS and LLL1 2 3 expressed their effects on VH respectively. Differences in VH among DIC and/or LLL were significant at the 1% with few exceptions. The effects of interactions: DIC X LLL on VH were significant at the 1% level in some cases. The maximum and minimum values of VH were found in the interactions: CM2DIS X LLL3 and TDIS X LLL1, respectively.
文摘应用Solid Works Flow Simulation软件对1款乳化头的4个不同定子结构进行了CFD(计算流体力学)分析,通过仿真计算,直观获得了釜内不同乳化头周围的流体速度分布云图和流线轨迹;通过粒子示踪法模拟了制胶物料在乳化头作用下的分布状态;最后在定子外围设定草绘面,并获取该面上的平均速度,以定量预测和对比不用定子结构的乳化效果。研究结果表明:通过CFD分析,可从4个方案中选择最佳结构的定子,从而达到优化定子的目的;在4个定子结构中,无顶梢且上宽下窄型出料口的定子具有相对最好的分散效果。
文摘跨介质航行体入水瞬间会受到巨大的冲击载荷,极易导致结构破坏甚至内部器件失灵。为发展有效的降载方法,本文基于VOF(Volume of Fluid)多相流模型,研究头部喷气航行体入水过程的载荷特性和流体动力特性,分析喷气压力、喷气高度对降载效果的影响,并探索头部喷气降载方法有效性的入水速度范围。研究结果表明,头部喷气使自由液面下凹形成空腔,并能极大地降低航行体所受阻力和冲击力,延缓了航行体撞水时间,从而实现冲击载荷控制;喷气压力和喷气高度对入水空泡形态及冲击压力峰值的影响都不大,合理的选择既能达到降载效果又能节约喷气量;入水速度为50 m/s时,降载量高达76.51%,但当入水速度为300 m/s时,降载量仅为39.92%。因此,针对高亚声速跨介质入水问题,需进一步探索主被动相结合的复合降载方法。
