Sedimentation of a single particle between two parallel walls

The sedimentation of a single circular particle between two parallel walls was studied by means of direct numerical simulation (DNS) and experiment. The improved implementation of distributed Lagrange multiplier/fictitious domain method used in our DNS is a promising new way for simulation of particulate flows. The settling behaviors of the particle are presented ranging in Reynolds number from 0 to about 700, which showed that our results for low Reynolds numbers agreed well with that reported before. Nevertheless, for higher Reynolds numbers our results were different from theirs. The long-term mean equilibrium positions in our results were all on the centerline, but not at off-center position as reported before. In order to validate our simulation, experiments were also conducted. The results showed that the sedimenting behavior simulated in this paper agreed well with our experiment result.     

Influence of coherent structures in the gas-particle circular cylinder wake flow

INTRODUCTION Turbulent gas-particle flows are frequently found in natural phenomena and industrial processes.Cases of cylinders in cross flows with particles occur in heat exchange equipment,including the convective zone of a fluidized-bed combustor,and in the primary superheaters,reheaters,and economizers of coal-fired boilers.Coherent structures often occur in the above-mentioned gas-particle flow,and have great effect on such different systems,while some features of tur-bulent multiphas…     

Large eddy simulation of a particle-laden turbulent plane jet

Gas-solid two-phase turbulent plane jet is applied to many natural situations and in engineering systems. To predict the particle dispersion in the gas jet is of great importance in industrial applications and in the designing of engineering systems. A large eddy simulation of the two-phase plane jet was conducted to investigate the particle dispersion patterns. The particles with Stokes numbers equal to 0.0028, 0.3, 2.5, 28 (corresponding to particle diameter 1 μm, 10μm, 30μm, 100μm, respectively) inRe=11 300 gas flow were studied. The simulation results of gas phase motion agreed well with previous experimental results. And the simulation results of the solid particles motion showed that particles with different Stokes number have different spatial dispersion; and that particles with intermediate Stokes number have the largest dispersion ratio. Project (No. G19990222) supported by the Special Funds for Major State Basic Research of China     

Motion and orientation of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio

Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles.     

Performance investigation of 2D lattice Boltzmann simulation of forces on a circular cylinder

The lattice Boltzmann method (LBM) is employed to simulate the uniform flow past a circular cylinder. The performance of the two-dimensional LBM model on the prediction of force coefficients and vortex shedding frequency is investigated. The local grid refinement technique and second-order boundary condition for curved walls are applied in the calculations. It is found that the calculated vortex shedding frequency, drag coefficient and lift coefficient are consistent with experimental results at Reynolds nu...     

Application of factor difference scheme to solving discrete flow equations based on unstructured grid

A second-order mixing difference scheme with a limiting factor is deduced with the reconstruction gradient method and applied to discretizing the Navier-Stokes equation in an unstructured grid. The transform of nonorthogonal diffusion items generated by the scheme in discrete equations is provided. The Delaunay triangulation method is improved to generate the unstructured grid. The computing program based on the SIMPLE algorithm in an unstructured grid is compiled and used to solve the discrete equations of two types of incompressible viscous flow. The numerical simulation results of the laminar flow driven by lid in cavity and flow behind a cylinder are compared with the theoretical solution and experimental data respectively. In the former case, a good agreement is achieved in the main velocity and drag coefficient curve. In the latter case, the numerical structure and development of vortex under several Reynolds numbers match well with that of the experiment. It is indicated that the factor difference scheme is of higher accuracy, and feasible to be applied to Navier-Stokes equation.     

Lagrangian time scales and its relationship to Eulerian equivalents in turbulent channel flow

Lagrangian and Eulerian time scales were obtained from the direct numerical simulation of turbulent channel flow at two Reynolds numbers based on the friction velocity and channel half-height, Rer= 80, 100. The Lagrangian integral time scales and time microscales were compared to their Eulerian equivalents. It is found that the ratio of Lagrangian to TL Eulerian integral time scales is given by TE/TiE= 1 ＋ 0.1y＋ for y＋ ≤ 10, and that the ratios between the Lagrangian to theEulerian time microscales are almost the same irrespective of the components. Those increase with y＋ are approximated by ≈ 2.75 - 1.75 exp （-v＋/a） . These results also show that these expressions are independent of the Reynolds number.     

Recent development of vortex method in incompressible viscous bluff body flows

INTRODUCTION A number of problems involve flows of gases orliquids over bluff bodies such as air flowing over carsand airplanes and wind blowing over bridges andbuildings. Many experiments or simulations havefocused on the above problems. In those phenomena,flows will not follow the solid bodies completely, butseparate from them and create wakes. The generationand shedding of large coherent vortex structures dueto flow separation make the bluff body flows complexand very difficult …     

Large eddy simulation of the gas-particle turbulent wake flow

INTRODUCTIONPlanewakeflowisonetypeoffreeshearflowandexistswidelyinnatureandmanyengi neeringsystems.Tounderstandthekineticchar acterofthelarge scalecoherentvortexstructuresandparticledispersioninplanewakeflowishelpfulforimprovingmanyprocessesinenergyengineering,chemicalengineeringandmaterialengineering .LargeeddysimulationinvolvesbothdirectsimulationandReynolds averagedapproaches.MethodshavebeendevelopedinrecentyearstosolvetheproblemofinstantaneousgasflowfieldandtosimulatehighReynoldsnumb…     

DNS系统在校园网中的应用研究

DNS在Internet互联网的发展过程中起了重大的推动作用,成为网络正常运行的重要条件.阐述了DNS的工作原理,提出了它在校园网中的几个应用问题,同时结合我们的工作经验,通过一个实例说明了校园网DNS系统的建立,最后对DNS查询作出了分析研究.     

Numerical simulation of interaction between laminar flow and elastic sheet

A numerical simulation of the interaction between laminar flow with low Reynolds number and a highly flexible elastic sheet is presented. The mathematical model for the simulation includes a three-dimensional finitevolume based fluid solver for incompressible viscous flow and a combined finite-discrete element method for the three-dimensional deformation of solid. An immersed boundary method is used to couple the simulation of fluid and solid. It is implemented through a set of immersed boundary points scattered on the solid surface. These points provide a deformable solid wall boundary for the fluid by adding body force to Navier-Stokes equations. The force from the fluid is also obtained for each point and then applied on the boundary nodes of the solid. The vortex-induced vibration of the highly flexible elastic sheet is simulated with the established mathematical model. The simulated results for both swing pattern and oscillation frequency of the elastic sheet in low Reynolds number flow agree well with experimental data.     

拉曼光谱法检测微量乙烯气体

首次利用激光拉曼技术对微量乙烯气体进行测试和分析,得到500 cm-1~3500 cm-1内乙烯气体的拉曼光谱。结果表明,乙烯气体的拉曼光谱有明显特征峰,这一性质为进一步研究果蔬散发乙烯气体的检测提供了依据。     

RLC串联谐振频率测定方法新探

通过理论分析和实验,提出了一种较为准确的测定RLC串联谐振电路谐振频率的方法,并进行了计算机仿真,结果与理论分析一致。该方法具有原理清楚、准确性高的特点。     

Numerical and Experimental Study on Nugget Formation Process in Resistance Spot Welding of Aluminum Alloy

The weld nugget formation in the resistance spot welding(RSW) of aluminum alloy was investigated in the present study. The nugget formation process was directly observed by using a digital high-speed camera. Numerical simulation was also employed to investigate the nugget formation process. The results showed that for the RSW of two aluminum alloy sheets, a nugget was first formed in the workpiece/workpiece(W/W) interface and grew along the radial direction and axial direction of the sheets, and then it became a large elliptical nugget. For the RSW of three aluminum alloy sheets, two small nuggets were firstly formed in two W/W interfaces and grew along the axial direction and radial direction; finally they fused into one nugget. Besides, there existed a critical welding time, after which the nugget size remained nearly unchanged. This indicates that a long welding time is unnecessary for the RSW of aluminum alloy. In addition, the calculated nugget radius was compared with the experimental results, which showed that the simulation results agreed well with the experimental results.     

计算机房的优化管理设计与应用

计算机已成为高校教学、科研工作不可缺少的重要组成部分，根据该校实验教学中心繁重的实验教学任务情况，阐述了如何充分利用管理软件、VLAN技术、DNS技术及现有设备资源为教学、科研服务。     

Pressure drop in a packed bed with sintered ore particles as applied to sinter coolers with a novel vertically arranged design for waste heat recovery

The pressure drop over a packed bed with sintered ore particles was studied experimentally. The sintered ore particles were characterized to determine their equivalent particle diameter, bed voidage, and sphericity. The pressure drop experiments were performed on unsorted and sieved particles with various size distributions for a superficial velocity up to 2.4 m/s, covering flow regimes from laminar to turbulent. It was shown that the Ergun equation underestimates the pressure drop for such highly irregular-shaped particles by about 40%. The measured modified friction factor was well correlated to a scaled Ergun equation, which was verified to be valid for the modified particle Reynolds number up to 12 000 toward design and optimization of vertically arranged sinter coolers for waste heat recovery.     

纳米KNbO3粉体的水热合成及表征

给出了一个在Nb-K-H2O三元体系中水热合成KNbO3的新的工艺条件；讨论了水热反应温度、溶液初始浓度及反应时间对合成产物的组分及形态等的影响；采用水热合成方法，在KOH浓度3M以上、反应温度为250℃、反应时间24h时，成功合成了钙钛矿结构KNbO3纳米陶瓷粉体；X射线衍射（XRD）、透射扫描电子（TEM）分析表明，水热合成的KNbO3晶粒发育完整，平均粒径为40nm；FT-IR、FT-Raman光谱等测试结果表明，纳米尺度KNbO3晶粒的Nb-O特征振动吸收带和拉曼位移分别出现了宽化和蓝移现象．     

Numerical Simulation on Nugget Formation and Evolution in Spot Welding of Aluminum Alloy

With the squeeze of electrode tips, the oxide film on aluminum (Al) alloy surface is broken and numbers of micro-gaps are formed randomly. The micro-gaps act as conducting spots at the beginning of welding, so the contact resistance is extremely high and unstable in spot welding of Al alloy. In this paper, a new contact resistance model is adopted to simulate the nugget forming process. This model describes the random distribution characteristic of conducting spots. The simulation results indicate that, within the first 5 ms of welding current (AC, 50 Hz), the temperature distribution at the workpieces interface is seriously irregular. In addition, the nugget does not nucleate from the weld center and grow continuously, however, it nucleates randomly from several points almost instantaneously and then merges into an entity quickly. Experimental results agreed with the numerical simulation.     

CFD Simulation of the Filtration Performance of Fibrous Filter Considering Fiber Electric Potential Field

Aiming at disclosing the quantitative effects of Coulomb forces on the filtration efficiency of aerosol particles, a three-dimensional random fiber model was established to describe the microstructure of fibrous filters. Then, computational models including the flow model, particle model, and electric field model were constructed to estimate the filtration efficiency using the Fluent custom user-defined function program, neglecting the non-uniformity of the fiber potential and the particle charge distribution. The simulation results using the established models agreed with the data in the literature. In particular, the electric field force was found to be one of the important factors required to improve the filtration efficiency estimation accuracy for the ultrafine particles. Moreover, the variation tendencies of the filtration efficiency and the pressure drop of fibrous filters were studied based on the influence factors of the fiber potential, particle charge-to-mass ratio, solid volume fraction, fiber diameter, and face velocity. The established models and estimated results will provide important guidance on the design of high-efficiency particulate air filters for aerosol particles.     

基于小波分析和神经网络的胎儿心电提取

通过小波分析方法和自适应线性神经网络相结合,对围产期母体腹壁混合心电信号进行处理,采用两种方案进行仿真并分析对比。分别采用小波变换和小波包分解技术对心电信号消噪处理,探索一种提取出胎儿清晰心电信号的方法,为下一步胎儿心电信号特征提取和健康状况的诊断奠定基础。实验结果表明,先提取胎儿心电信号,再进行消噪处理效果较好。