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25 May 2020, Volume 37 Issue 3 Previous Issue    Next Issue
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Numerical Validation of Three Reduced Kinetic Mechanisms of Methane Air Mixture YU Yize, XU Shengli, ZHANG Zhuhe, ZHANG Mengping 2020, 37(3): 253-262.  DOI: 10.19596/j.cnki.1001-246x.8061 Abstract ( )   HTML ( )   PDF (1697KB) ( )   Methane and air premixed combustion around a cylinder is chosen to evaluate reduced mechanisms of 16species/41steps, 15species/19steps and 53spesies/325steps. The coming flows are homogeneous. Turbulence and its interaction with combustion, fuel diffusion are neglected and finite reaction rates of chemistry are assumed in the computation. The 5th order WENO scheme that conserves free flow properties is used to mitigate derivative errors from unsmooth grids and increase solution accuracy. Pressure and temperature contours as well as their distributions along stagnation line are obtained including mass fractions of species CH4, CO and CO2. Bow shock and flame front both appear upstream the cylinder. Standoff distances and induction lengths are related to reduced mechanisms. With increasing cylindrical diameter, standoff distances increase and induction length decrease either for ignition delay. The bow shock and flame are both pushed upstream but they are still remained in sequence. In contrast to reduced models of 16species/41steps and 15species/19steps, 53spesies/325steps model provides good accuracy and ignition covers a wide range of pressure and temperature. Three models demonstrate incompletely burning or chemical reactions in all cases except cases of cylinders with large diameters. It shows that elementary reactions reach chemically equilibrium but the reactions are not so completely. Meanwhile, the larger cylindrical diameter, the better accuracy in evaluation of reduced chemistry mechanisms.

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Influence of Heating Size and Rayleigh Number on Natural Convection in a Deformable Open Cavity:Lattice Boltzmann Method TANG Guyue, LOU Qin, LI Ling 2020, 37(3): 263-276.  DOI: 10.19596/j.cnki.1001-246x.8046 Abstract ( )   HTML ( )   PDF (5115KB) ( )   Natural convection problem in a deformable outlet cavity is studied with lattice Boltzmann method. Heated size at left wall are set to two conditions: The whole wall (H) and the middle wall (0.5H). The right wall is open to external environment. The upper and lower boundaries are adiabatic and their right end can be moved up and down to adjust size of the right outlet. Effects of Rayleigh number (104 ≤ Ra ≤ 106), the right exit size (1.0H ≤ L ≤ 2.0H), the left wall heating size (Lh=0.5H or Lh=H) on streamlines, isothermal lines, local Nusselt numbers and average Nusselt numbers are investigated. It shows that heat transfer in the cavity increases with the increase of Rayleigh number, which manifests as size of elliptical quasi-stationary region in the cavity increases and is closer to the upper and lower adiabatic boundaries. Thickness of thermal stratification is gradually reduced and average Nusselt number is increased. However, increase of the right outlet has a different degree of influence on heat transfer effect in the cavity. As the heating size is in the middle of the left wall surface, size of the right side opening does not significantly affect the heat exchange. In addition, at the left wall heating size of 0.5H it shows a higher average heat transfer efficiency. An empirical prediction of functional relation between average Nusselt number and control parameters is proposed. The fitting function satisfies practice and design in projects.

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Three-dimensional Numerical Simulation of Dynamics Characteristics of Two Rising Bubbles with Lattice Boltzmann Method HU Yu, SUN Tao 2020, 37(3): 277-283.  DOI: 10.19596/j.cnki.1001-246x.8048 Abstract ( )   HTML ( )   PDF (6318KB) ( )   Dynamics characteristics of two bubbles in a quiescent fluid were simulated with three-dimensional lattice Boltzmann model. Eight-point and eighteen-point difference schemes were used to calculate the first and the second order derivative ▽ φ and ▽2φ in order to avoid numerical instability caused by large density ratios. It shows that for two rising bubbles with same size, the leading bubble rises like an isolated bubble, and the trailing bubble is influenced by the wake of the leading bubble. For two rising bubbles with different sizes, however, the larger bubble always strongly affects the smaller one in any initial sizes and locations.

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Aero-optical Effects in Supersonic Compression Ramp Flow Fields:GCV-FFT Method ZHOU Zhichao, XU Lingfei, REN Tianrong, GU Cunfeng 2020, 37(3): 284-298.  DOI: 10.19596/j.cnki.1001-246x.8065 Abstract ( )   HTML ( )   PDF (27207KB) ( )   Supersonic compression ramp flow is studied. Based on Rytov approximation, a generalized convolution-fast Fourier transform (GCV-FFT) method is used to solve directly Helmholtz equation in inhomogeneous medium. Scattering field of the laser beam and complex amplitude distribution of diffracted field are obtained. Aero-optical parameters including light intensity, optical path difference, Strehl ratio, relative light intensity, beam centroid position and effective beam width are given. It can be seen that the laser beam is transmitted in the turbulent flow field, and the light intensity distribution appears gradually undulates and deviates. As passing through flow field, the beam produces a large degree of distortion, deviation and breakage due to the effect of diffraction. Effect of flow field in compressed ramp region on beam quality is significantly greater than that in fully developed turbulent region. From distribution of relative light intensity, the beam breakage seems to be related to small-scale coherent structure of flow field. The error of Strehl ratio obtained by traditional OPD mean square error or weighted mean square error estimation is greater. More accurate method should be evaluated with PSF method.

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Lattice Boltzmann Simulation of Fast Phase Change in Ultrashort Laser Drilling WANG Zimo, LI Ling 2020, 37(3): 299-306.  DOI: 10.19596/j.cnki.1001-246x.8056 Abstract ( )   HTML ( )   PDF (6318KB) ( )   Lattice Boltzmann model with double distribution function is used to study fast phase-change heat transfer in single-pulse laser metal drilling process. Flow and heat transfer of the melted metal material is considered and an immersion moving boundary scheme was used to track solid-liquid interface in the process. Pure heat conduction model and heat transfer model considering convection are used to simulate the process and the results are compared with experimental data. It shows that flow of the melted material has a great impact on phase change heat transfer during laser drilling and results with model that considers flow heat transfer are closer to experimental data. Melting rate, melting depth and temperature field distribution were analyzed, and effects of laser parameters on phase transition process were discussed. It shows that at the end of a pulse, the larger the pulse width of laser, the smaller hole depth, the larger aperture, and the lower temperature of shorter pulse laser are found.

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High-order Fully Implicit Scheme and Multigrid Method for Two-dimensional Semilinear Diffusion Reaction Equations ZHANG Lin, GE Yongbin 2020, 37(3): 307-319.  DOI: 10.19596/j.cnki.1001-246x.8042 Abstract ( )   HTML ( )   PDF (13831KB) ( )   A finite difference method is used for high-order numerical solution of two-dimensional unsteady semilinear diffusion reaction equation. The spatial derivative term is discretized by a fourth-order compact difference formula, and the time derivative term is discretized by a fourth-order backward Euler formula. An unconditionally stable high-order five-level fully implicit scheme is proposed. Truncation error of the scheme is O(τ4+τ2h2+h4), that is, the time and space have fourth-order accuracy. In calculation of start-up steps, the first, second and third time levels are discretized by Crank-Nicolson method. Richardson extrapolation formula was used to extrapolate startup time accuracy to the fourth-order. A multigrid method based on the scheme is established, which accelerates convergence speed of the algebraic equations on each time level and improves computational efficiency. Finally, accuracy, stability and efficiency of the scheme and multigrid approach are verified with numerical experiments.

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Collocation Spectral Method for Radiative Heat Transfer in One-dimensional Cylindrical Medium with Graded Index WU Ming, ZHOU Ruirui, LI Benwen 2020, 37(3): 320-326.  DOI: 10.19596/j.cnki.1001-246x.8028 Abstract ( )   HTML ( )   PDF (699KB) ( )   We develop a collocation spectral method (CSM) to address radiative transfer in a semitransparent anisotropic scattering cylindrical medium with graded index and space-dependent albedo. Accuracy and validity of the method is verified with exact solutions available in literature and other methods. CSM is found effective in obtaining radiative flux in graded index medium. And few nodes are enough to obtain accurate results.

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Salt-body Classification Method Based on U-Net LU Xinrui, HUANG Handong, LI Shuai, YIN Long 2020, 37(3): 327-334.  DOI: 10.19596/j.cnki.1001-246x.8044 Abstract ( )   HTML ( )   PDF (7387KB) ( )   Convolutional neural network has made great breakthroughs in the field of computer vision. With its powerful image processing ability,we transform classification of underground sedimentary salt-body into image semantics segmentation problem. Deep convolution neural network is applied to implement pixel-level semantics segmentation of salt seismic images. We increase depth of the network and adds batch normalization and Dropout processing based on U-Net, which makes the neural network model with higher reliability and stronger generalization ability. With experiments, it was found that adding batch normalization layer after convolution layer, and adding Dropout after the pooling layer and concatenate layer improve steadily segmentation performance of the model for salt-body seismic image.

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Volume Estimation of Crust-Mantle Interface Beneath Lunar Nearside Mare Basins Based on Spherical Harmonic Algorithm ZHONG Zhen, ZHANG Teng, XIAO Wenjun 2020, 37(3): 335-340.  DOI: 10.19596/j.cnki.1001-246x.8049 Abstract ( )   HTML ( )   PDF (2914KB) ( )   We propose a method of volume estimation based on spherical harmonic coefficients of compensated topography. It shows that volume of compensated topography depends merely on sum of coefficients between compensated topography and windowed constant height. The algorithm shows a simplification of computation and improves efficiency of estimation. Moreover, it demonstrates smaller error than general numerical methods. It can be employed in estimating volume of compensated topography windowed with various shapes. This method provides a good reference for estimation of lunar parameters, especially the elastic thickness over mare basins.

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A Heat Exchanger Network Optimization Strategy for Internal Utility Evolution JIANG Yiwen, CUI Guomin, BAO Zhongkai, LIU Huolin, ZHOU Jinjia 2020, 37(3): 341-351.  DOI: 10.19596/j.cnki.1001-246x.8060 Abstract ( )   HTML ( )   PDF (1841KB) ( )   There is an infeasible structure in heat exchanger network optimization in which matching temperatures of cold and hot streams are crossed. Replacing matching by internal utilities is a way to deal with infeasible structure and its solution domain can be expanded. This approach introduces additional fixed investment costs in total annual cost which may be accepted in weaker solutions, which may cause a decrease of optimization efficiency. Therefore, we analyze firstly probable bad influence caused by internal utilities and propose an evolutionary strategy for internal utilities. Total annual cost of the solution which has internal utilities are punished to reduce the accepting probability. If the solution with internal utilities still exist, then heat loads of internal utility exchangers are forced to evolve to optimize the heat load and improve its structure. Effectiveness of the strategy is verified with two examples.

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Quantum Transport in a Carbon Nanotube Transistor:Influence of Two Charged Defects in Dielectric WEI Zhichao, WANG Nengping 2020, 37(3): 352-364.  DOI: 10.19596/j.cnki.1001-246x.8054 Abstract ( )   HTML ( )   PDF (6332KB) ( )   Nonequilibrium Greens function method in a tight-binding approximation is used to calculate current through a carbon nanotube field-effect transistor (CNFET) with cylindrical gate electrode. Two individual defects in gate oxide (SiO2) of a long channel p-type CNFET is investigated. It is found that the relative current reduction and the threshold voltage shift caused by two charged defects depend sensitively on positions of the charged defects. If the charges Q1=Q2=+e (where -e is electron charge) are both close to one of the two leads, or one is close to the source lead and the other is close to the drain lead, the relative current reduction in on-state is much greater than that due to a single positive charge Q=+e located close to one of the two leads. In this case, the threshold voltage shift due to two charges is negligible. If two positive charges are both around center of the channel, the relative current reduction in on-state caused by two charges is significantly greater than that caused by a single positive charge near center of the channel. Furthermore, the negative shift of threshold gate voltage increases with decreasing distance between two charges. And a great threshold voltage shift of -0.35 V may be caused.

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Raman Scattering Modification in Monolayer Arsenene Controlled byStrain Engineering ZHAO Yicheng, GUO Junhong, HU Fangren 2020, 37(3): 365-370.  DOI: 10.19596/j.cnki.1001-246x.8057 Abstract ( )   HTML ( )   PDF (5342KB) ( )   Raman spectra of monolayer arsenene with external strain are determined with density functional theory. Due to lower structural symmetry, deformation induced by external strain regulates Raman mode splitting and leads to Raman mode shifts as well. Our calculations suggest that the structural deformation induced by external strain can be clearly identified by Raman scattering.

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A Comparative Study of Analytical and Numerical Dispersion Relations of Fibonacci Sequence One-dimensional Photonic Crystals LI Yan 2020, 37(3): 371-378.  DOI: 10.19596/j.cnki.1001-246x.8047 Abstract ( )   HTML ( )   PDF (1502KB) ( )   A transfer matrix method is used to analytical calculation formulas of photonic band and equifrequency surface of one-dimensional Fibonacci sequence photonic crystal. Analytical physical quantities such as equivalent phase refractive index, group velocity and wave vector are given. Dispersion relations of this kind one-dimensional photonic crystal are studied contrastively with formulas and finite difference time domain method. It shows that results obtained by numerical method and analytical method are consistent with each other in overall trend. However, in weakly modulated one-dimensional photonic crystal, fatal error was made in numerical calculation result of equifrequency surfaces. Therefore, numerical results of weakly modulated photonic crystals must be verified with other methods such as analytical calculation or numerical simulation.