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25 September 2015, Volume 32 Issue 5 Previous Issue    Next Issue

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A Nonlinear Iterative Method for Energy Equations with Piecewise Smooth EOS HANG Xudeng, LI Shuanggui, YANG Rong, YUAN Guangwei 2015, 32(5): 505-513.  Abstract ( )   PDF (2807KB) ( )   In practical applications, equation of states (EOS) consists of several piecewise smooth surfaces, which leads to discontinuity at interface. As a traditional nonlinear iterative algorithm is applied to an energy equation with discontinuous EOS, it may lead to slow convergence and unphysical solutions. To overcome the difficulties, a nonlinear problem is designed, and a nonlinear iterative algorithm is proposed to solve the problem. The algorithm is fit for energy equations with discontinuous EOS of piecewise smooth functions. A parameter of energy change is defined in the algorithm so that it is unnecessary to know discontinuity position in advance. The algorithm calculates precisely net gain or leakage of energy, which can be used to assess influence of discontinuity in EOS. Typical numerical experiments verify that the algorithm converges stably, and gives physical solutions.

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Uncertainty Quantification of Numerical Simulations Subjected to Calibration MA Zhibo, YIN Jianwei, LI Haijie, LIU Quan 2015, 32(5): 514-522.  Abstract ( )   PDF (881KB) ( )   Propagation analysis often overrate uncertainty of numerical simulation, especially as many uncertain inputs exist. Taking advantage of the reality that calibration can reduce epistemic uncertainty of system-level numerical simulation, a method for uncertainty quantification is offered synthetically using comparison information based on available test data and additional propagation information of modeling and simulation. An example with virtual test is displayed in which the method is demonstrated and validated.

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WENO Based Entropy Stable Scheme for Shallow Water Equations CHENG Xiaohan, NIE Yufeng, CAI Li 2015, 32(5): 523-528.  Abstract ( )   PDF (1567KB) ( )   A high resolution scheme is presented for shallow water equations. The scheme is based on entropy stable numerical flux with high order weighted essentially non-oscillatory (WENO) reconstruction at cell interfaces. A strong stability-preserving Runge-Kutta method is employed to advance in time. Several benchmark numerical examples demonstrate that the scheme is accurate and non-oscillatory.

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Test Particle Monte Carlo Simulation of Return Flux on Spacecraft Surfaces due to Ambient Scatter of Outgassing Molecules JIN Xuhong, HUANG Fei, CHENG Xiaoli, WANG Qiang 2015, 32(5): 529-536.  Abstract ( )   PDF (2926KB) ( )   Test particle Monte Carlo (TPMC) method is presented. Return flux on four geometric surfaces due to ambient scatter of outgassing molecules is simulated. Return flux ratio (RFR) obtained for flow past a sphere is in good agreement with DSMC results. RFR on outgassing and freestream conditions for flows past three geometric bodies, including a circle flat plate, a convex and concave hemisphere, is investigated. RFR for flows past a circle flat plate and a concave hemisphere is much greater than that for flows past a convex hemisphere. Outgassing molecules collide on outgassing surfaces directly forming direct flux contamination for flows past concave surfaces, which is much greater than RFR. Thus, using convex outgassing surfaces in spacecraft design can decrease return flux contamination effectively.

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Unsteady Interaction on Flat Plate/Isolated Roughness Element in Hypersonic Flow PAN Honglu, GUAN Faming, YUAN Xiangjiang, BU Junhui 2015, 32(5): 537-544.  Abstract ( )   PDF (4436KB) ( )   For separation controlling in hypersonic turbulence flow, flat plate/roughness element interaction is studied with large eddy simulation (LES). Unsteady flow characteristics behind roughness element are analyzed. Flow stability is investigated with roughness element flow field in different height and diameter conditions. Simulation indicates that intensity inverse pressure grads are generated due to roughness element interaction in hypersonic boundary flow. In high free shear layer, inconsistent stable characteristic is influenced by height of roughness element:Short cylinder roughness element interact with flat plate boundary layer induces shock wave/boundary layer interaction and produces a free shear layer, while free shear layer is stable downstream. However, free shear layer induce by long cylinder roughness element is instable. It evolves into K-H vortex in stream-wise. On the other hand, average friction coefficient and heat-flux coefficient on flat surface interacted by roughness element are lower behind roughness element(k=1.0δ), which could be applied in anti-heat and anti-drag of aircraft inlet.

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Simulation of a Pair of Bubbles Rising Side by Side Using VOSET Method LI Longjian, ZHANG Lei, ZHU Wenbing, SHEN Xianwen 2015, 32(5): 545-552.  Abstract ( )   PDF (2624KB) ( )   A numerical simulation was performed to investigate two bubbles rising side by side in vertical channel using VOSET (Coupled Volume-of-Fluid and Level Set) method and N-S equations coupled with continuous surface force (CSF) model. Behaviors of coalescence between two identical bubbles predicted were in good agreement with experimental results reported in literature. Effects of surface tension on trajectories and velocities during rising process are investigated. Three types of motion were observed depending on surface tension:Coalescence, two bubbles repeatedly attracted and bounced against each other, bounced and separated. Without coalescence, trajectory shows symmetry about channel center line. Vertical velocities of both bubbles are almost the same while magnitude of horizontal velocity with opposite direction equals.

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Lattice Boltzmann Simulation of Gas Bubble Merging in Three Dimensions LV Yaqi, NIE Deming, LIN Jianzhong 2015, 32(5): 553-560.  Abstract ( )   PDF (3296KB) ( )   Equilibrium distribution functions for lattice model D3Q15 are proposed in the framework of lattice Boltzmann method in free energy model. Bubble merging process is studied. It shows that bubble merging not only depends on initial bubble distance, but also depends on surface tension. The greater the surface tension is, the greater the critical distance for bubble merging. Furthermore, influence of initial bubble distance, surface tension and viscosity on merging velocity are investigated.

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A Detached Eddy Simulation Model for Free Surface Flows with Uneven Bottom ZHANG Jingxin 2015, 32(5): 561-571.  Abstract ( )   PDF (3862KB) ( )   A detached-eddy simulation (DES) model is proposed based on a fully hydrodynamic pressure model instead of hydrostatic model. The numerical scheme is based on finite volume method (FVM) on unstructured grids in the horizontal plane, and σ coordinate in vertical direction to fix free surface and uneven bottom. The in-house codes are paralleled using OpenMP. The proposed model is shown particularly effective in prediction of small-scale vortical structures.

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Effects of Water Content on PAM/PVA Interpenetrating Network Hydrogel Performance WEI Qinghua, WANG Yanen, YANG Mingming, CHAI Weihong, ZHANG Yingfeng 2015, 32(5): 572-578.  Abstract ( )   PDF (2489KB) ( )   To study interpenetrating network hydrogel system of PAM/PVA, molecular dynamics simulation is made to investigate molecular interaction inside a hydrogel system. Effects of water content on PAM/PVA composite hydrogel performance are studied. It is found that cohesive energy density and binding energy of hydrogel system increase with water content increasing. Meanwhile elastic coefficients, engineering modulus and ductility decreased with increasing of water content. In addition, with analysis of pair correlation function, we found that there are mainly hydrogen bonding interactions between H2O molecules and surrounding atoms or functional groups. Strengths of hydrogen bonds formed are Owater >OPVA >OPAM >NPAM, which consists with possibility (difficulty) of forming hydrogen bond.

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Influence of Run-time on Water/Oil Vacuum Separation CHEN Bin, LIU Ge, ZHANG Xianming 2015, 32(5): 579-585.  Abstract ( )   PDF (4258KB) ( )   To study influence of run-time on dynamic characteristics of water/oil separation, a mathematical model is established to describe flow field in vacuum oil purifier. Evaporation of droplet phase transition equations are established, considering effect of three-phase flow of oil/water/vapor and water droplets evaporation phase change. Influences of run-time on oil/water/vapor three-phase volume fraction distribution and axial dehydration rate are analyzed. Dynamic characteristics of oil/water/vapor three-phase flow at different run-time is indicated. Efficiency of dehydration of water/oil separation is enhanced with run-time. It provides a foundation for further research on water/oil separation mechanism in vacuum oil purifier.

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Finite Analytic Numerical Method for Two-Phase Incompressible Flow in 2D Heterogeneous Porous Media ZHENG Xiaolei, LIU Zhifeng, WANG Xiaohong, SHI Anfeng 2015, 32(5): 586-594.  Abstract ( )   PDF (4283KB) ( )   A finite analytic numerical scheme is constructed for two-dimensional two-phase flow in heterogeneous porous media. Compared with traditional numerical methods, FAM makes convergence faster as refinement parameter increases, and accuracy is independent with heterogeneity. In contrast, as using traditional numerical schemes to simulate flow through a strong heterogeneous porous medium, refinement ratio for grid cell needs to increase dramatically to get an accurate result. Compared with the proposed scheme, traditional numerical scheme underestimates greatly breakthrough time under coarse grids. However, to get a saturation distribution with high resolution even employing the proposed scheme, relative fine grids are still needed. This is different from FAM for solving a single phase flow, where coarse grids provide rather accurate results.

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Linear Element Method for Multi-angle Fractured Horizontal Well in Anisotropic Reservoir FANG Sidong, CHENG Linsong, XIN Yinan, HE Congge 2015, 32(5): 595-602.  Abstract ( )   PDF (2739KB) ( )   With Green function and Laplace transformation, one-dimensional element is established considering effect of permeability tensor of anisotropic reservoir. Inflow of fracture is obtained by linear interpolation of endpoints and flow in fracture is treated with linear integral of flow rate. Coupling flow in formation and fractures, calculating method for bottom-hole pressure is formed semi-analytically. It shows that there are three flow regimes including fracturing linear flow, formation linear flow and system radial flow. The more the fractures, the less the dimensionless pressure and number of factures has significant impact on flow rate. With increase of fractures increasing rate is dropping in the same time. Fracture length and conductivity have similar characteristics. Flow rate is improving as angle between fracture and wellbore is increasing. Flow rate reaches maximum as fracture is perpendicular to wellbore, and vice versa. Angle between maximum permeability and fracture has similar impact on production. In summary, production rate reach maximum as fracture is perpendicular to wellbore and direction of maximum permeability.

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Reduced-order Model Based on Cluster Analysis in Numerical Simulation of Low Permeability Reservoir ZHANG Yanyu, LI Weiwei, CHEN Huijuan 2015, 32(5): 603-609.  Abstract ( )   PDF (2166KB) ( )   A mathematical model for numerical simulation of 2D water-oil phase reservoir concerning start-up pressure gradient is solved with full implicit finite difference scheme. A reduced-order model is established by projecting original model in low dimension space formed by basis functions, which is produced from collected snapshots; CVT-Lloyd algorithm is employed in cluster analysis to tackle with flaws from collecting snapshots of same time interval. Computational results show that reduced-order model established based on POD is able to approximate the original model effectively. With cluster analysis, data reduction is eliminated, which could create uniform snapshots in space resulting in enhanced accuracy of reduce-order model. On the other hand, extremely limited clustering groups may lead to loss of information and thus impairing accuracy of reduced-order model.

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Spectroscopic Properties of SiCl (X2Π, A2Σ+) Radical LIU Hui, XING Wei, SHI Deheng, SUN Jinfeng, ZHU Zunlue 2015, 32(5): 610-616.  Abstract ( )   PDF (649KB) ( )   Potential energy curves (PEC) of ground X2Π and A2Σ+ states of SiCl radical are calculated with internally contracted multireference configuration interaction approach in combination with Dunning's correlation-consistent basis sets. Reference energy and correlation energy are extrapolated to complete basis set limit. Scalar relativistic and core-valence correlation corrections are calculated. Spectroscopic parameters of X2Π and A2Σ+ states are obtained. With Breit-Pauli operator, PECs of X2Π1/2 and X2Π3/2 states are computed. Spectroscopic parameters of two Ω states are determined. Vibration manifolds are evaluated for two Λ-S and two Ω states of non-rotation SiCl radical by numerically solving radical Schrödinger equation of nuclear motion. For each vibrational state, vibrational levels and inertial rotation constants, spin-orbital coupling constants of X2Π state are determined.

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Stabilization of Double Tearing Mode by External Current Drive YANG Zhen, LU Xingqiang, GONG Xueyu 2015, 32(5): 617-622.  Abstract ( )   PDF (2877KB) ( )   Effects of external current drive on instability of double tearing mode in Hall MHD equations are numerically investigated. It shows that double tearing mode can be suppressed by antiparallel external current drive at x-point of tearing mode magnetic islands. Periodic external current drive controls island width under a threshold and stabilizes double tearing mode. With increasing period depression effect becomes worse. If frequency, density and width of periodic external current drive are adopted suitably, depression effect becomes better.

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Modified Genetic Algorithm for Identifying Material Thermal Properties and Strength of Heat Source YAN Fan, LU Mei 2015, 32(5): 623-630.  Abstract ( )   PDF (2040KB) ( )   A mathematical model for two-dimensional nonlinear inverse heat conduction problem (IHCP) is established. Three kinds of genetic algorithm at different modified phase are proposed for identifying material thermal conductivity and strength of heat source. Convergence speed and calculation precision of genetic algorithms at different modified phase are compared. Calculation results show that the genetic algorithm modified strategy proposed achieve higher convergence speed and calculation precision.