ENO守恒插值(重映)方法及其在流体计算中的应用

在ENO(Essentially Non-oscillatory)守恒插值方法的基础上,分析和研究现今流体力学计算中涉及的几类网格技术:重叠网格技术、自适应加密技术和运动网格技术.基于ENO插值多项式构造的重映方法具有良好的守恒性,可以有效保证数据传递中物理量的总体守恒.提出该类守恒插值方法在以上几种网格技术中的一些应用前景,并给出一些数值算例.     

Electroosmotic Flow, Ionic Currents, and Pressure-Induced Flow in Microsystem Channel Networks: NMR Mapping and Computational Fluid Dynamics Simulations

Using nuclear magnetic resonance (NMR) velocity mapping and NMR current density mapping as well as finite-element computational fluid dynamics methods, transport in microsystem electrolytic cells with increasing complexity has been examined ranging from single straight channels to random-site percolation clusters. This sort of system is considered as paradigm for more or less complex devices in microsystem technology. Corresponding model objects were designed on a computer and milled into ceramic (polar) or polystyrene (nonpolar) matrices. The pore space was filled with electrolyte solutions. Maps of the following quantities were recorded: velocity of hydrodynamic flow driven by external pressure gradients, velocity of electroosmotic flow (EOF), ionic current density in the presence of EOF, ionic current density in the absence of EOF. As far as possible, the experiments were supplemented by computational fluid dynamics simulations. It is shown that EOF, as well as the electric current, leads to recirculation patterns in closed complex structures such as percolation clusters. Remarkably, all transport patterns turned out to be dissimilar, and the occurrence and positions of eddies do not coincide in the different maps. Velocity histograms and the mean velocity as a function of the porosity have been evaluated. An EOF percolation transition is found at the geometrical percolation threshold. The combined application of NMR techniques for the quantitative, noninvasive visualization of the total variety of hydroand electrodynamics in the same channel system promises to become a powerful tool for design purposes in microsystem technology. Authors' address: Rainer Kimmich, Sektion Kernresonanzspektroskopie, Universit?t Ulm, Albert-Einstein-Alee 11, 89069 Ulm, Germany     

基于流-热耦合模型的GMM智能构件温升控制系统设计

热效应对超磁致伸缩执行器中超磁致伸缩材料性能产生非常大的影响,从而影响超磁致伸缩执行器的定位精度;提出一种简化的强制水冷策略保证磁致伸缩材料温度恒定;同时建立了超磁致伸缩材料智能构件流-热多场耦合的有限元模型,运用COMSOLMultiphysics 3.4软件对模型进行仿真,仿真结果验证了模型的正确,进一步的实验结果证实了提出的温度控制策略的有效性。     

基于CFD和FEM方法的刷式密封传热特性研究

采用计算流体动力学与有限元分析相结合的方法,数值研究了压差和干涉量对刷式密封传热特性的影响规律。刷式密封的温度分布是通过求解基于Non-Darcian多孔介质模型的Reynolds-Avergaed Navier-Stokes(RANS)方程获得。刷丝与转轴的摩擦热量是通过摩擦系数、法向接触力和接触速度计算得到。刷丝与转轴接触力是通过对刷式密封非线性接触模型进行有限元分析计算获得。研究结果表明,在干涉量一定时,刷丝与转轴法向接触力随压差增大呈线性增加,刷丝的最高温度随压差增大而显著升高,但最高温度的上升趋势随压差增大而减缓;在压差一定时,刷丝与转轴法向接触力随着干涉量增大而略微增大,最高温度随干涉量增加而小幅上升。     

Optimisation and Efficiency Improvement of Electric Vehicles Using Computational Fluid Dynamics Modelling

Due to the rise in awareness of global warming, many attempts to increase efficiency in the automotive industry are becoming prevalent. Design optimization can be used to increase the efficiency of electric vehicles by reducing aerodynamic drag and lift. The main focus of this paper is to analyse and optimise the aerodynamic characteristics of an electric vehicle to improve efficiency of using computational fluid dynamics modelling. Multiple part modifications were used to improve the drag and lift of the electric hatchback, testing various designs and dimensions. The numerical model of the study was validated using previous experimental results obtained from the literature. Simulation results are analysed in detail, including velocity magnitude, drag coefficient, drag force and lift coefficient. The modifications achieved in this research succeeded in reducing drag and were validated through some appropriate sources. The final model has been assembled with all modifications and is represented in this research. The results show that the base model attained an aerodynamic drag coefficient of 0.464, while the final design achieved a reasonably better overall performance by recording a 10% reduction in the drag coefficient. Moreover, within individual comparison with the final model, the second model with front spitter had an insignificant improvement, limited to 1.17%, compared with 11.18% when the rear diffuser was involved separately. In addition, the lift coefficient was significantly reduced to 73%, providing better stabilities and accounting for the safety measurements, especially at high velocity. The prediction of the airflow improvement was visualised, including the pathline contours consistent with the solutions. These research results provide a considerable transformation in the transportation field and help reduce fuel expenses and global emissions.     

Hydrodynamics Analysis of a Folding Sieve Tray by Computational Fluid Dynamics Simulation

In this reported work, a new type of tray, a folding sieve tray (FST), consisting of duplicated perforated oblique planes folding at a specific angle was designed. A three-dimensional two-fluid CFD model was employed to predict the hydrodynamics performance of a 0.6 m FST at different folding angles (48° and 90°) and opening ratios (10.2%, 12.5%, and 15.0%), compared with a 0° unfolding-structure sieve tray (ST). The models used in this study were within the two-phase Eulerian framework to ensure that the gas and liquid phases were an interpenetrating continuum. To verify the reliability of the models, the simulation results were compared with experimental results and were found to be in good agreement, and the relative error was less than 10%. The backmixing, pressure drop, clear liquid height, froth height, entrainment and the details of the gas–liquid distributions on the tray were investigated. Better operational stability was found in FST that resulted from the better liquid distribution, a lower pressure drop across the tray, and a relatively smaller clear liquid height. It was shown that gas in the FST had a higher horizontal velocity near the holes to guide the liquid phase. About 90% of backmixing, 50% of clear liquid height, and 30%of wet tray pressure drop were reduced in the FST.     

高温气冷堆堆芯球床流动与温度分布均匀性研究

由于燃料球的随机分布和球床的壁面效应,球床式高温气冷堆堆芯孔隙率分布会有一定的不均匀性。深入认识壁面漏流、随机孔隙率对球床温度分布均匀性的影响对进一步提高高温气冷堆冷却剂出口温度及其安全性具有重要意义。本文采用多孔介质模型实现了对堆芯球床壁面漏流、随机孔隙率效应的数值模拟。结果表明,由于壁面漏流效应,壁面附近局部区域冷却剂最大速度会比中心高50%,对球床温度影响则不大。中心区域局部极小、极大孔隙率只对很小区域内流速和温度有影响,但温度变化幅值很小。球床中心随机孔隙率使冷却剂速度波动小于13%,对球床温度影响很小。     

燃烧流场线CARS测温技术研究

常规CARS采用凸透镜聚焦多束激光于空间一点,在满足相位匹配条件下产生携带该点温度信息的CARS信号。常规CARS一次只能测量一个空间点的温度,难以满足燃烧流场深入研究需要。为了提高CARS测量能力,使得CARS在一次测量中获得更多信息,提出了线CARS测量方法。线CARS测量方法在常规CARS基础上采用柱面凸透镜替换普通凸透镜,使得聚焦位置由焦点变为焦线。由于焦线上的点大部分满足相位匹配关系,因此可以同时获得多点CARS信号。后续光路同样采用柱面凸透镜替换普通凸透镜,通过光谱仪和ICCD相机将CARS信号传输至计算机,解析出聚焦线上CARS信号对应的温度信息,实现CARS测量能力由“点”到“线”的提升。基于平面火焰炉的燃烧实验结果表明：线CARS可以一次有效测量200个空间点的温度信息,空间测量长度约3.6 mm,空间分辨率约18 μm,测量结果相对不确定度优于7%,在保持测量精度的同时有效丰富了单次测量信息。     

基于有限单元法和计算流体动力学的光机热集成仿真分析研究

使用计算流体动力学、传热学、固体弹性力学和光学的多物理场耦合集成仿真分析技术完成了红外热像仪中光机的热特性与热设计研究.采用有限单元法(Finite Element Method,FEM)和计算流体动力学(Computational Fluid Dynamics,CFD)得到了光机内部的温度场、应力变形分布及光学件面形...     

基于平行投影法的三维流场重建

在行处理方法的基础上提出了一种基于平行投影的迭代方法，对传统的行处理方法不同，它不是通过向某一超平面作垂线进行迭代，而是作某个超平面的平行线与另一超平面相交进行迭代。与传统方法相比，它明显加快了迭代速度。     

三分螺旋折流板换热器壳侧流场温度场模拟

建立了三分螺旋折流板换热器壳侧流动与传热的数学模型,对其流场、温度场和压力场的数值模拟结果在多个纵剖面和横切片上进行了展示。可见在螺旋通道的轴心和靠近壳体的折流板外缘区域局部速度较高,在折流板背流面呈现出有利于强化掺混作用的回流区,流道内几乎没有流动死区;壳侧流体温度为稳步均匀下降趋势,并呈现从圆周的外缘向轴心方向逐渐递减;而压力场则呈现明显的周期性和阶梯性。     

Computational Model of Thermal‐Fluid Flow in a Radio‐Frequency Plasma Torch

The paper aims to clarify the modelling results concerning the heat transfer and fluid flow in a radio‐frequency plasma torch with argon at atmospheric pressure. Fluid numerical simulation requires the coupling of magnetohydrodynamics (MHD) and thermal phenomena. This model combines Navier–Stokes equations with the Maxwell's equations for compressible fluid and electromagnetic phenomena successively. A numerical formulation based on the finite element method is used. In this study, fluid flow and temperature equations are simultaneously solved (direct method, instead of using the indirect method) using a finite elements method (FEM) for optically thin argon plasmas under the assumptions of local thermodynamic equilibrium (LTE) and laminar flow. Appropriate boundary conditions are given, and nonlinear parameters such as the thermal and electrical conductivity of the gas and input power used in the simulation are detailed. We have found that the source of power is located on the torch wall in this type of inductive discharge. The center can be heated by conduction and convection via electromagnetic phenomena (power loss and Lorentz force). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于相位展开的三维流场干涉层析术

提出用傅里叶变换进行干涉图相位展开（ＰｈａｓｅＵｎｗｒａｐｐｉｎｇ）的办法直接恢复变形波面，从而可以提取轴向任意截在上的投影数据，实现真正意义上的三维层析，模拟温度场实验证明基于相位展开的投影数据提取方法能够更好的完成层析计算。     

Simulation of Nanoparticle Production in Premixed Aerosol Flow Reactors by Interfacing Fluid Mechanics and Particle Dynamics

The interaction of fluid mechanics and particle dynamics at the very early stages of flame synthesis largely affects the characteristics of the product powder. Detailed simulations provide a better understanding of these processes, which take place in a few milliseconds, and offer the possibility to influence the product characteristics by intelligent selection of the process parameters. The present paper reports on the simulation of titania powder formation by TiCl₄ oxidation in an aerosol flow reactor. A commercially available fluid mechanics code is used for the detailed calculation of the fluid flow and the chemical reaction at non-isothermal conditions. This code is then interfaced with a model for aggregate particle dynamics neglecting the spread of the particle size distribution. The simulation shows the onset of the particle formation in the reactor and calculates the dynamic evolution of the aggregate particle size, number of primary particles per aggregate and the specific surface area throughout the reactor. The presented, newly developed calculation technique allows for the first time the simulation of particle formation processes under the authentic, complex conditions as found in actual aerosol reactors.     

一种新型的基于磁性液体的光纤Sagnac磁场传感器

提出一种使用磁性液体的新型光纤Sagnac磁场传感器.磁性液体具有磁致可变双折射效应和二向色性,在外加磁场作用下,液体中的磁性纳米粒子沿磁场方向结链规则排列,形成各向异性.将其制成液体薄膜,放入具有一段保偏光纤的Sagnac环中,使光纤Saganc干涉仪的正弦形状干涉光谱可随外磁场变化.光纤中传输光垂直经过磁性液体薄膜...     

基于拉格朗日跟踪法的波纹流道流体特性研究

采用正交实验方法考察了具有不同结构参数的三维周期波纹流道中的流体性能,并采用Webb评价方法对其进行性能评价。比较了不同波纹宽度的波纹流道的阻力因子e_f、传热因子e_Nu和能效因子η的值,结果表明三者都随Re的增大而增大,波纹宽度最小时能效因子η最大。流体在波纹流道中垂直于主流方向的横截面上产生二次流,随着Re增大,二次流增强,阻力增大,温度边界层减薄,温度等值线分布变得不均匀,传热增强。采用拉格朗日粒子跟踪技术分析了不同Re下,流体粒子在波纹流道内的运动轨迹,绘制了不同周期出口流体粒子的庞加莱截面图,结果表明流体粒子在波纹流道中被反复拉伸和折叠,增加了流体粒子的接触面积,提高混合效率,强化了传热。     

基于Boltzmann光谱法的焊接电弧温度场测量计算

电弧等离子体是非均匀等离子体,其内部进行着复杂的能量和质量输运过程,等离子体的温度测量具有重要意义。Boltzmann作图法测量温度较谱线绝对强度法、标准温度法等测温方法更为方便。基于Boltzmann作图法原理,对TIG电弧进行实时的空间扫描,分析了谱线的选取原则,测量计算出TIG焊电弧等离子体的温度场分布。     

Particle Dynamics in an Electrohydrodynamic Flow Field investigated with a two-component laser-doppler velocimeter

A laser-Doppler instrument has been used to measure the migration velocity of NaCl particles in an electrohydrodynamic flow field of an electrical precipitator. The measured average migration velocity of 1.40-μm particles (number distribution median with a geometric standard devitation of 1.46) is approximately five to six times higher than the calculated steady-state velocity for a 1.40-μm particle, provided there is a saturation charge of at least 90f%. Further, the particle velocities in the main flow direction are also influenced by the electrical operation conditions. Both observations demonstrate the important role of the state of the electrohydrodynamic flow field (superposition of moving gas ions and neutral gas molecules) on the particle transport, characterized by the dimensionless electrohydrodynamic number N_EHD. A comparison between six different electrohydrodynamic states revealed that N_EHD ≈? 1 is a critical value for the mutual interactions between the gas ions and the neutral gas phase. Whereas for N_EHD values > 1 the stochastic particle motion is chiefly determined by the nonsteady-state character of the negative corona, for N_EHD values < 1 the particle velocity fluctuations are governed by the turbulence level of the neutral fluid. These finding might be helpful in adjusting the operating conditions in electrical precipitators for and optimized particle separation.