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25 January 2013, Volume 30 Issue 1 Previous Issue    Next Issue

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A Hybrid Method for Multiphase Flows with Large Density Ratio WU Jie, XU Shuang, ZHAO Ning 2013, 30(1): 1-10.  Abstract ( )   PDF (2415KB) ( )   In the framework of diffuse interface method (DIM), an efficient hybrid method for muhiphase flows with large density ratios is proposed. Lattice Boltzmann method is employed to obtain information of flow field. Cahn-Hilliard (C-H) equation is directly solved to identify the interface. In order to maintain stabihty of calculation at large density ratios, convection term of C-H equation is discretized by using second order unwind scheme. Numerical simulations of Rayleigb-Taylor (R-T) instability, bubble rising in liquid and droplet impact on a dry surface are implemented. The results agree well with data in literature.

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Lattice-Boitzmann Investigation of Rotating Turbulence NIE Deming, LIN Jianzhong, HUANG Lizhong 2013, 30(1): 11-18.  Abstract ( )   PDF (2337KB) ( )   Turbulence in the presence of rotation is numerically investigated with MRT-lattice Bohzmann method. Influence of rotation (Rossby number and Ekman number) on turbulence is studied in detail. Numerical results include turbulence energy, dissipation rate, iso-surface of velocity, vortex structure, dissipation length and integral length and so on. It shows that rotation slows down turbulence energy decaying rate. Moreover, the initial homogeneity of turbulence is broken down in the presence of rotation. Vortices rotating in opposite direction of the system are suppressed gradually and columnar vortices appear rotating in the same direction of the system eventually. In addition, it was found that Kolmogorov length decreases as rotation increases while integral length increases.

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Two-way Coupling Lattice Boltzmann Model for Gas-Particle Turbulent Flows WANG Haoming, ZHAO Haibo, ZHENG Chuguang 2013, 30(1): 19-26.  Abstract ( )   PDF (1384KB) ( )   An LB-based gas-solid two-phase model with two-way coupling is developed considering feedback forcing of particles in evolution equation of fluid particles. Smagorinsky subgrid model is also introduced in simulation of flow field with high Reynolds numbers. Classic particle-laden flow over a backward facing step is simulated and velocity profiles of gas phase and particles (considering one-way coupling and two-way coupling respectively) are compared with experimental results. The results of two-way coupling LB model are obviously better than these of one-way coupling LB model. Furthermore, preferential concentration of particles with different Stokes numbers (St) is investigated. It is found that small particles (St~0(0.1)) show better following behaviors with gas phase and are uniformly distributed in the flow field. Particles with moderate Stokes numbers (St~0(1)) are hard to be entrained into the vortex and show strong preferential concentration. On the other hand, large particles (St~0(10)) can enter into the vortex because of great inertial and are distributed more uniformly in flow field.

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An Explicit-implicit Algorithm for Ghost Fluid Method DING Yan, YUAN Li, YANG Li 2013, 30(1): 27-34.  Abstract ( )   PDF (1360KB) ( )   Based on operator splitting technique, Euler equations is splitted into convection part and non-convection part. A predicted solution is obtained by solving the convection part with explicit GFM method. It is corrected by an implicit pressure correction algorithm derived from the non-convection part. A second order primitive explicit-implicit algorithm is built. It shows that CFL condition can be relaxed and efficiency is improved.

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Particle Finite Element Method for Incompressible Multi-fluid Flows GAO Yongfeng, ZHANG Xiangyan, LIU Ning 2013, 30(1): 35-43.  Abstract ( )   PDF (1905KB) ( )   Particle finite element method (PFEM) is used to incompressible multi-fluid flows include arbitrary numbers of fluids. Identification of internal interfaces is a key. It is solved by subdivision of mixed elements which are divided into single-fluid elements. To adapt to different fluid properties, a stabilized formulation based on finite calculus procedure is used in fractional step method. Boundary point birth, particle velocity control, and automatically penetration check are used for preventing penetration. Accuracy and reliability of PFEM and interface identification measure are demonstrated with Rayleigh-Taylor instability test and collapse of water column. Finally, seven fluids mixing shows that mixing of an arbitrary number of immiscible fluids could be simulated easily.

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Realistic Heat Capacity Effects in Two Phase Aluminum Dust Detonations TENG Honghui, YANG Yang, JIANG Zonglin 2013, 30(1): 44-52.  Abstract ( )   PDF (463KB) ( )   Two phase detonations of aluminum dust are simulated in a multi-fluid model to study particle energy calculation methods. In previous studies heat capacities of solid particles are constants, while realistic heat capacities change with temperature. In this simulation, effects of realistic heat capacities are studied. Numerical results show that detonation parameters are influenced significantly. The results with realistic capacities are close to experiments, while the results with fixed capacities overestimate pressure and detonation velocity. In detonation initiation, run-up distance is mainly decide by ignition energy, while realistic effect makes the distance shorter than that in the fixed heat capacity case.

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Ejection and Sweep Flows in Transitional Boundary Layers CHEN Lin, YUAN Xiangjiang 2013, 30(1): 53-60.  Abstract ( )   PDF (2339KB) ( )   At late stages of compressible transitional boundary layers over a flat-plate, ejection and sweep flows are investigated by means of direct numerical simulation with high order accuracy. Numerical results with high resolution clearly represent complex phenomena of ejection and sweep flows in the transition process of boundary layers. Close relationships with typical vortex structures and spike structures are revealed. Details of formation mechanisms of ejection and sweep flows are analyzed. Numerical results demonstrate experimental findings. Corresponding mechanisms are analyzed.

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Numerical Study on Ground Effect of High Speed Trains SUN Zhenxu, GUO Dilong, YAO Yuan, YANG Guowei 2013, 30(1): 61-69.  Abstract ( )   PDF (2948KB) ( )   A steady RANS approach is adopted to investigate ground effect of high speed trains. Variation of aerodynamic forces due to ground effect is studied. Comparisons of aerodynamic forces on high speed train at different yaw angles and with different ground boundary conditions are performed. It reveals that aerodynamic forces at a yaw angle of 0° are severely affected by the ground effect. As the yaw angle increases, however, influence on aerodynamic forces due to ground effect gets weaker. Influence of height between bottom of the train and the ground is carefully studied. It shows that lift reversal phenomenon exists at different heights and pressure wave on bottom surface of the train takes a linear relation with heights.

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Drag Reduction on Micro-structured Superhydrophobic Surfaces SONG Baowei, GUO Yunhe, HU Haibao, SONG Dong 2013, 30(1): 70-74.  Abstract ( )   PDF (732KB) ( )   Numerical simulation on superhydrophobic surface of turbulent flow is shown. Velocity or shear stress of turbulent flow are provided and basic law between microscopic structure and drag reduction rate is analyzed. In simulation, we use an unsteady Reynolds averaged simulation model and VOF model for gas-liquid two phase flow. It shows that slip flow and cyclical shear stress exist on superhydrophobic surface. It can reduce resistance and increased resistance as well. Microstructure size has significant effect on drag reduction rate. In order to increase drag reduction rate, the aspect ratio of rectangular mierostructure should be greater than 3:2 and the groove spacing should be small, while the groove width should be less than 200 micron.

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Numerical Simulation of Turbulent Mass Transfer of Binary Electrolyte in an Electrode Channel ZHOU Xiaolan, LIU Caixi, DONG Yuhong 2013, 30(1): 75-81.  Abstract ( )   PDF (2303KB) ( )   Direct numerical simulations of binary electrolyte in an electrode channel with turbulent mass transfer are performed under limiting current condition and galvanostatic current conditions. Behaviors of turbulent concentration diffusion from electrodes to adjacent electrolyte in a wide range of Schmidt numbers are examined and mechanism of turbulent mass transfer in electrolytic processes is analyzed. A physical model for turbulent electrodes channel flow is established with electrochemistry theories as well as fluid dynamics. Effect of Schmidt numbers on turbulent mass transport, mean and fluctuating concentrations, mass transfer coefficient, Sherwood numbers, and instantaneous structures of concentration fields are exhibited and analyzed. It shows that mass transfer at electrodes in turbulent electrolyte is sensitive to current conditions.

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Thermonar Dynamics Simulation Method HU Guojie, CAO Bingyang 2013, 30(1): 82-88.  Abstract ( )   PDF (1828KB) ( )   We propose a simulation method, thermonar dynamics (TD) simulation. Thermons in ideal gases can be simulated directly by TD method. A collision model between thermons is established and thermodynamic properties of thermon gas are obtained. By TD simulation method, equilibrium and non-equilibrium thermon gas of argon are simulated. Simulated pressures of equilibrium systems agree with the equation of state of thermon gas predicted by thermomass theory. Simulated thermal conductivities are consistent with experimental and theoretical data. Feasibility of the proposed thermonar dynamics method is shown.

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Fast Monte Carlo Method for Particle Coagulation Dynamics XU Zuwei, ZHAO Haibo, LIU Xin, ZHENG Chuguang 2013, 30(1): 89-97.  Abstract ( )   PDF (553KB) ( )   We propose a fast random simulation strategy based on differentially weighted MC. The strategy improves computation efficiency significantly, and guarantees enough calculation accuracy, thus coordinates contradiction between computation cost and computation accuracy. The main idea is based on majorant kernel. It is possible to transfer a traditional coagulation kernel to a majorant kernel through splitting and amplifying slightly. The maximum of majornant kernel is obtained by single looping over all simulation particles. The maximum majornant kernel is used to approximate the maximum coagulation kernel in particle population, and is further used to search coagulation particle pairs randomly with acceptance-rejection method. The waiting time (time-step) for a coagulation event is calculated by summing coagulation kerenls of particle pairs involved in acceptance/rejection processes.. Double looping in normal Monte Carlo simulation is avoided and computation efficiency is improved greatly.

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Automobile Wind Noise Prediction Using Stochastic Method CEHN Rongqian, WU Yizhao, XIA Jian 2013, 30(1): 98-104.  Abstract ( )   PDF (1798KB) ( )   A stochastic method is used to predict wind noise of a simplified automobile head shape. In the method, computational region is divided into two parts: One is source region, and the other is propagation region. In the source region, turbulent fluctuation velocities are synthesized with a stochastic model. In the propagation region, linearized Euler equations with source terms are solved and sound waves spread out. Compared with direct simulation method, the method has advantage of less computational cost and memory. Numerical simulations agree well with experimental data. It is shown that the method is feasible for automobile wind noise prediction, It laid a foundation for actual automobile shape wind noise prediction.

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Uncertainty of Coherent Acoustic Field in Shallow Water CHENG Guangli, ZHANG Mingmin, HU Jinhua 2013, 30(1): 105-110.  Abstract ( )   PDF (1753KB) ( )   A method using stochastic response surface method is presented. It solves wave equation with uncertain parameters in shallow water. Uncertain parameters of ocean environment are expressed with standard stochastic variables. And stochastic response of coherent sound field is expressed by Hermite multinomials. An approximate expression of coherent sound field is achieved with coefficients of stochastic muhinomial solved by probabilistic collocation method. It shows that the proposed method is more accurate and efficient than Monte Carlo method and field shifting method.

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Convergence Analysis on Splitting Iterative Solution of Multi-group Radiation Diffusion Equations HANG Xudeng, LI Jinghong, YUAN Guangwei 2013, 30(1): 111-119.  Abstract ( )   PDF (1860KB) ( )   We give a convergence analysis on splitting iterative (SI) algorithm of multi-group radiation diffusion equations. Spectral radii of iterative matrix is shown. Numerical computation and analysis on spectral radii formulae reveal a relation between convergence rate and radiation coefficients. Numerical results confirm theoretical results, and give applicable conditions of the algorithm.

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Diffusion Approximation of Steady Radiative Transport in Graded Index Media LIU Lijun, ZHAO Junming 2013, 30(1): 120-126.  Abstract ( )   PDF (361KB) ( )   A diffusion approximation equation was derived for steady radiative transport in graded index media. With discretization and finite element method, steady radiative heat transfer in two-dimensional rectangular gray semitransparent medium are examined to verify performance of the diffusion approximation. Cases with uniform index distribution and graded index distributions are considered. Boundary radiative heat flux and media temperature distribution under radiative equilibrium are determined with diffusion approximation and compared with results of radiative transfer equation. It shows that accuracy of the diffusion approximation is influenced by index, scattering characteristics,optical depth and scattering albedo. As the medium is optical thick and scattering is strong, the diffusion approximation shows good accuracy and can be considered as a rapid algorithm for steady radiative transfer problem in a semitransparent graded index medium.

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Kalman Filter in Track Reconstruction Algorithm for Time Projection Chamber LI Bo, GAO Yuanning, YANG Zhenwei, LI Yulan 2013, 30(1): 127-133.  Abstract ( )   PDF (1338KB) ( )   A straight-line track model is developed, and validity of Kalman filter track reconstruction algorithm with the track model was verified in detail. It shows that given sufficient hits track parameters converge to true values. The track reconstruction program is implemented in MarlinTPC reconstruction framework in practice. By choosing track reeonstruction parameters reasonably, the program discriminates noise efficiently and reconstructs tracks. The algorithm is valuable in track reconstruction of large prototypes.

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Hybrid Method for Electromagnetic Wave Transmission Through Fractal Layered Rough Surfaces TIAN Wei, REN Xincheng, GUO Lixin 2013, 30(1): 134-139.  Abstract ( )   PDF (1765KB) ( )   Electromagnetic wave transmission through 1D band-limited Weierstrass fractal rough surfaces of layered medium is investigated with a hybrid method based on method of moment (MoM) and Kirchhoff approximation (KA). The upper rough surface and the under rough surface are divided into MoM region and KA region, respectively. Transmission coefficient as a function of scattering angle of transmission wave is obtained. Influences of fractal dimension, height root mean square, permittivity of substrate medium, permittivity and mean layer thickness of intermediate medium, frequency of incident wave on transmission coefficient are discussed. It shows that transmission coefficient is affected by parameters of upper rough surface considerably.

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Parallel Implementation of Fast Multipole Methods for Three-dimensional Potential Fields on JASMIN ZUO Fengli, LIU Xu, ZHANG Baoyin, HU Xiaoyan 2013, 30(1): 140-147.  Abstract ( )   PDF (953KB) ( )   A parallel software module of FMM (fast multipole method) for three-dimensional Laplace kernel functions, JASMIN-3DLapFMM, is designed and implemented. The module is based on two phases parallel strategy of both processes and threads. A parallel software module is successfully used to solve the far field potential of electrostatic fields. With a fixed problem size of single processor,almost linear weak parallel scalability is obtained for a grand scale problem with 1010 particles on more than ten thousand processors. With a fixed size of total problem and 1024 processors, about three times speedup is obtained on four threads.

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Stability, Electronic and Magnetic Properties of ZnS Nanotubes:A Comparative Study CHEN Hongxia, LIU Chenglin 2013, 30(1): 148-158.  Abstract ( )   PDF (3389KB) ( )   Electronic and magnetic properties of ZnS nanotubes (NTs) were investigated systematically using first-principles approach. A double-wall NT (DWNT) with hexagonal cross section (HCS) shows higher stability, while zigzag and armchair NTs with round cross section (RCS) show lower stability than single-wall NT (SWNT) with HCS. Electronic band structures show that they are direct band gap semiconductors. With hydrogen adsorption, SWNT with HCS transform into indirect band gap semiconductor. Magnetic properties of ZnS NTs doped with transition-metal(TM) atoms (Cr, Mn, Fe, Co, and Ni) are calculated. Formation energies of doped NTs are smaller than those of the pristine ones, indicating that doing process is an exothermic reaction. All NTs have atom-like magnetic moments mainly due to 3d component of the TM atoms. Monodoped NTs have potential utility in materials with tunable magnetic properties.