防风栅对高速列车挡风作用的数值模拟

该文采用CFD数值模拟的方法研究了防风栅对高速列车的挡风作用。首先,根据附加源项法的基本原理,将防风栅等效为多孔介质,给出了对其挡风性能模拟的高效方法,通过与风洞试验对比,验证了该方法的有效性。在此基础上,研究了不同开孔率防风栅下游的流场特征,结果表明,40%开孔率的防风栅挡风性能较好。然后,应用动网格技术,仿真得到列车运行状态下的气动力,对比表明该文得到的列车气动力与实测结果相吻合。最后,通过脱轨系数和轮重减载率,评估了40%开孔率的防风栅遮挡下高速列车在横风作用下的安全性,结果表明,该种防风栅提高了列车在强风区的运行效率。     

线性装药聚能射流成型过程无网格MPM法数值模拟

线性装药聚能药柱起爆后能产生高速射流,为了研究线性装药聚能药柱的爆轰和射流的形成过程,该文应用无网格MPM法进行三维数值模拟,采用显式算法对爆轰产物和射流的速度、密度以及压力分布进行了数值计算。无网格MPM法与有限元和其他无网格法相比,能获得比较好的模拟结果,而且在数值计算效率方面具有优势。     

网格划分对叉排管束摩擦阻力系数的影响

应用流体计算软件FLUENT,对受限空间内烟气冲刷叉排管束(横竖均为5排,间距比均为1.25)的流动进行了数值模拟研究,主要研究了三角形和四边形非结构化网格及四边形结构化网格划分对流场流动摩擦阻力系数f的影响。结果表明:结构化网格相对于非结构化网格,虽然建模时间较长,但网格生成速度快,计算耗时短,易收敛且精度高;对于同类型网格,网格边界层底层厚度及圆周节点数的选取均对模拟结果存在较大影响。     

弹簧近似法在二维非结构动网格生成技术中的应用

通过控制网格质量改进弹簧近似法,并将其结果与传统方法进行比较。数值模拟结果显示：基于弹簧近似法的非结构动网格随着模型边界旋转角度的增加网格质量逐渐下降;在发生相同旋转角度时,改进弹簧近似法生成网格的质量较传统方法有了较大的改善;传统弹簧近似法模型边界最大旋转角度为13°左右,改进方法可达到27°,较大地提高了网格的变形能力。最后,运用改进的弹簧近似法对二维翼型进行数值模拟,并与传统方法及实验数据进行比较,得到了较满意的结果,该方法能够较好地运用于实际数值模拟中。     

大规模四面体网格并行生成方法

针对大规模网格串行生成的时间和内存瓶颈问题,阐述了一种非结构化四面体网格并行生成方法,首先对几何体进行初始网格划分,并通过相对体积比及最优分区控制初始网格数量;然后采用图论图划分方法对初始网格进行区域分解;最后采用分裂法进行并行网格生成。提出的基于共享单元的边界判定方法,有效地解决了分区边界节点的匹配问题。通过算例证明了该并行网格生成方法具有良好的并行效率,同时可以产生高质量的四面体网格。     

三维高超声速稀薄气体流场通量分裂式DSMC-IP方法研究

结合非结构网格对复杂外形精确描述的能力和IP（Information Preservation）方法降低统计耗散的特点,该文在非结构网格的基础上构建了改进型通量分裂式DSMC（Direct Simulation of Monte Carlo）-IP数值方法,对三维高超声速稀薄气体流场进行了数值模拟。采用渐变尺度的非结构网格划分流场区域,在满足DSMC方法对网格尺度需求的同时,对流场的结构特点进行精确描述;另外根据Van Leer格式的思想改进IP方法中的通量计算格式,解决了激波处的数值间断问题;并采用单元信息保存法对IP方法进行补充,提高了计算方法的稳定性。通过对三维圆球绕流和航天飞机头部绕流流场的数值模拟,验证了该文方法的有效性和可行性,并对模型中的气动特性和参数分布规律进行了分析。     

高速列车外部流场和车内噪声模拟计算

研究表明,高速列车气流噪声主要取决于车身表面脉动压力,所以研究列车车身表面脉动压力对进一步研究和控制高速列车气流噪声具有重要的意义。采用有限元法对高速列车外流场进行数值模拟,计算结果反映高速列车外流场特性。在此基础上,进一步对高速列车表面脉动压力进行数值模拟计算,并通过声固耦合的方法得到车内某点的声压级,得到一些有意义的结论。     

基于重叠网格的三维车桥系统气动特性研究

该文基于重叠网格方法,建立了移动列车的数值模型,研究了横风作用下三维车桥系统的绕流气动特性。通过与相关试验和文献对比,验证了重叠网格方法可以较好地模拟列车的运动;然后对横风作用下车桥系统的绕流流场进行分析,讨论了考虑列车运动后车桥气动力的变化。研究结果表明:由于列车风与横风的叠加以及车桥之间的气动干扰,使车桥系统横风绕流流场发生明显的改变;列车运动对前方空气的压缩作用使头车所受气动力最大,同时桥梁气动力也会发生突变。     

基于传输方程空化模型的定常自然空化流场数值计算

采用基于传输方程的空化模型，应用自主开发的软件对水翼和水下回转体定常自然空化流场进行了数值计算。采用基于压力修正和多块结构化网格的有限体积方法数值求解Favre平均的NS方程，运用k-ε两方程加壁函数的湍流模式封闭雷诺应力。计算结果与已有实验结果符合较好。     

基于非结构化网格同位有限体积法的粘弹流体数值模拟

采用基于非结构化三角网格的同位有限体积法模拟了聚合物溶液平板收缩流。其中,聚合物溶液微观尺度大分子的信息通过FENE-P本构模型得以在宏观场上体现。数值求解过程中,速度与压力、速度与应力间的耦合通过动量插值实现。通过与结构化网格数值结果及实验结果的比较,验证了该方法在粘弹流动问题求解中的正确性。与此同时,文中根据构象张量给出了分子微观结构直观的可视化描述方法,并分析了不同流动区域分子形变以及分子取向等微观信息。     

Analysis of the particle collision behavior in spiral jet milling

Collision behaviors of particles in spiral jet milling were analyzed by using a simulation. The motion of the particles was tracked by the discrete element method (DEM), and the air flow was represented by the computational fluid dynamics (CFD). The DEM was coupled with the CFD by a one-way coupling method. The simulated air flow was validated by comparing the fluid velocity field with the measured one in a model experiment. Furthermore, the air flow and particle behaviors in a spiral jet mill used commercially were analyzed by using the simulation. As a result, the particles with a region balancing between centrifugal and radial drag forces could be mainly ground by the high-speed collisions between the particles circulating near the top and bottom walls of the grinding chamber.     

膜式燃气表内部流动数值模拟研究

采用CFD数值模拟方法对有柔性膜片的膜式燃气表内部流动进行数值模拟研究,解决了皮膜和旋转阀之间的联动关系以及旋转阀转动与皮膜运动的仿真实现等技术问题;运用滑移网格、动网格及用户自定义函数(UDF)技术实现了膜式燃气表内部流动的动态数值模拟,获得了旋转阀与阀座存在1mm间隙的情况下膜式燃气表内部流场和仪表压损数据.结果表明,数值模拟技术用于膜式燃气表这种复杂结构的内部流动研究是可行的.     

Simulation of air-to-refrigerant fin-and-tube heat exchanger with CFD-based air propagation

A new model for simulating air-to-refrigerant fin-and-tube heat exchangers with computational fluid dynamics (CFD)-based air propagation is introduced. This model is based on a segment-by-segment approach and is developed to be a general purpose and flexible simulation tool. The model superimposes a CFD mesh on the heat exchanger model’s geometric grid, interprets the CFD results, and processes them to generate the air propagation path through the heat exchanger. The model is capable of accounting for air flow maldistribution and other complex flow patterns including recirculation zones within the heat exchanger, as well as, entrainment of exit flow into the heat exchanger, using both two-dimensional (2D) and three-dimensional (3D) CFD results. The modeling results show that the overall predicted heat load using 3D-CFD simulation results agrees within ±4% of the experimental data, without employing any multipliers on air side correlations.     

上下冲击式高效鼓风冻结装置速度场的数值模拟与验证

对上下冲击式高效鼓风冻结装置建立数学物理模型,使用CFD软件对速冻装置内静压箱和贴近网带上下方的速度场进行数值模拟。计算中将位于上下均风孔板间的网带作为多孔介质处理。研究结果表明,增设导流板可改进静压箱拐角处气流组织的均匀性;扩大冻结区两侧隔板和网带侧边形成的通道,也可以改进局部区域流场的均匀性,这种改进方法需要减小网带宽度或加大装置整体宽度。因此,要保证设备的冻结能力,则需综合考虑风速、网带尺寸等对冻结能力的共同影响。此外,网带位置会影响周围气体流场分布,网带距下方送风口距离在20 mm-30 mm之间时,可以保证风速在3 m/s左右,且均匀性较好。通过测试实验验证了模型建立的合理性及计算结果的准确性。     

气动发动机缸内流场特性研究

以全新研制的电控气动发动机气缸流场域为研究对象,建立其几何模型,运用CFD前处理软件ICEM对流场域几何模型进行网格划分,再运用Fluent动网格技术进行动态模拟计算,分析其气缸内部流场特性,进而得出气体在工作过程中各个阶段的压力场和速度场分布.同时,将模拟计算数值与气动发动机台架实验所得值进行比较.结果表明:动网格数值模拟结果与实验结果较为接近,气动发动机气缸内流场动态仿真过程准确可靠,仿真结果可为气动发动机设计提供参考.当转速稳定于450r/min时,由仿真模拟所得数据计算得此气动发动机指示功率为0.62kW,实验时测算得同条件下实验指示功率为0.55kW,求得仿真和实验指示功率的最大误差为11.2%.利用自制的测功装置测得实验时有效功率为0.45kW,进而求得机械效率为81.8%.研究结果为下一步改善气动发动机性能提供了依据.     

DEM Simulation of Particle Comminutionin Jet Milling

A combined discrete element method (DEM) and CFD numerical model was developed to simulate particle comminution in a jet mill. The DEM was used to simulate the motion of the particles in the gas flow. For this, the compressible Reynolds Averaged Navier-Stokes (RANS) equations were used to describe the gas flow field inside a given size's jet mill. Ghadiri's models for breakage and chipping were implemented in the simulation to define the reduction of the particle's size during jet milling. The size distributions of the particles after grinding were obtained numerically. The prediction of the numerical simulation for the median particle size d 50 after grinding was qualitative compared with experimental results for the different operating conditions (i.e., feed rate, angle of grinding nozzles, volumetric rate of grinding air, etc.). The comparison shows good agreement with the experimental observation. The results shows that the feed rate, angle of feeding nozzle, and feeding air's flow rate have more influence on the breakage and chipping of particles in jet milling. In addition, a parametric study was performed to obtain the desired operation conditions.     

气流分级机流场的数值模拟与优化

运用计算流体力学数值模拟的方法,研究气流分级机的内部气流流场情况,并对于分级机的工作参数进行优化。通过采用滑移网格技术模拟分级轮在气流分级机内的旋转,用结构网格与非结构网格结合的方法对气流分级机进行网格划分,主要研究了分级轮不同叶片数(4、6、12片),不同转速(500、1000、2000、3000r/min)下分级机内部流场情况并给出了相关解释。通过对不同参数的比较给出了优化的参数。模拟结果表明,分级轮转速越高、叶片数越多,分级效果越好。     

箱梁断面静风力系数的CFD数值模拟

用计算流体力学(CFD)方法模拟了桥梁跨中断面周围的风场特征,不仅能得到流场的压力、速度和涡旋的分布,还提取了箱梁断面的三分力系数。分别采用不同密度网格划分对主梁断面进行数值模拟,并将数值模拟结果与风洞试验值进行比较,选取最合理的网格划分方法。然后,对某一大跨度桥梁跨中断面的箱梁模拟了从-5°至+5°共11个整数度风攻角工况的三分力系数。并将数值模拟结果与风洞试验进行了对比,给出了不同攻角下的压强和速度分布,验证了采用CFD技术模拟桥梁三分力系数方法的可行性与可靠性。     

Novel discretization methods for improved simulation precision in injection molding

Mold filling is an important stage of injection molding, which is one of the most commonly used manufacturing processes for the production of thermoplastic components in high volumes. As a consequence, the numerical simulation of this process based on computational fluid dynamics (CFD) is of great significance for production engineering [1, 2]. However, modeling of the mold filling is a tremendously demanding process, when considering interfacial physical phenomena, such as two‐phase flows, building a sharp interface between the molten plastics and the present air in the cavity or the dynamic wetting contact line at the cavity surface. A method for dealing with these phenomena is a local mesh refinement both in space and time. In this paper, the numerical solution of a mold filling problem using simplex‐type space‐time finite elements is presented and compared with experiments. These elements can be suited to increase efficiency, when used for the aforementioned refinement. In addition, a Navier's slip boundary condition is applied to the solid boundaries of the mold allowing the contact line to evolve along the boundary, while enabling a better prediction of the pressure distribution. The presented work was performed in collaboration of the subprojects B3 and B5 of the collaborative research center 1120 “Precision Melt Engineering”.     

DEM Simulation of Particle Comminutionin Jet Milling

A combined discrete element method (DEM) and CFD numerical model was developed to simulate particle comminution in a jet mill. The DEM was used to simulate the motion of the particles in the gas flow. For this, the compressible Reynolds Averaged Navier-Stokes (RANS) equations were used to describe the gas flow field inside a given size's jet mill. Ghadiri's models for breakage and chipping were implemented in the simulation to define the reduction of the particle's size during jet milling. The size distributions of the particles after grinding were obtained numerically. The prediction of the numerical simulation for the median particle size d 50 after grinding was qualitative compared with experimental results for the different operating conditions (i.e., feed rate, angle of grinding nozzles, volumetric rate of grinding air, etc.). The comparison shows good agreement with the experimental observation. The results shows that the feed rate, angle of feeding nozzle, and feeding air's flow rate have more influence on the breakage and chipping of particles in jet milling. In addition, a parametric study was performed to obtain the desired operation conditions.