NUMERICAL SIMULATION ON DENSE GAS-PARTICLE RISER FLOW

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Large eddy simulation of the gas-particle turbulent wake flow

To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particle-laden wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0.15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures.     

Large eddy simulation of the gas-particle turbulent wake flow

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

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.     

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.     

三角形结构对液膜流动特性影响的数值模拟

基于VOF方法,利用CFD软件FLUENT对倾斜壁面上二维气-液两相流进行数值模拟,分析了三角形高度和结构间距均为1mm的6种尺寸壁面上的液膜流动特性,获得了三角形结构的壁面上液膜自由液面的分布图以及不同结构宽度w对液膜流动特性的影响规律。结果表明:与平壁面上液膜流动相比,三角形结构壁面上液膜自由液面位置随三角形结构呈规律性变化;在三角形结构壁面上,气体漩涡存在于液膜和壁面之间,当三角形结构宽度w改变时,漩涡的形状和位置均发生变化。     

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…     

下行床及提升管催化裂化数学模拟

该文提出了一维轴向扩散模型,并结合气因循环流化床中下行床及提升管的基本流体力学规律与四集总反应动力学模型,对提升管及下行床反应器用于瓦斯油催化裂化过程进行了模拟。计算结果表明,气体轴向运混对汽油收率有很大影响,汽油收率对Ｐｅｃｌｅｔ准数在０．１～１０００之间时变化较敏感。相同条件下,瓦斯油的转化率在 Ｐｅ＝４（提升管）中比 Ｐｅ＝ １００（下行床）约低 １０％。当瓦斯油的转化率提高时,气体轴向运混对汽油收率的影响更大。     

壳体结构LCM工艺的树脂流动的数值模拟

为了弥补实验研究树脂在三维壳体预制体中流动的空缺,采用数值模拟的方法进行研究。构建抛物面壳模型,采用控制体有限元法对含沉浸项的质量守恒方程进行求解,并用MATLAB程序模拟恒压条件下树脂在壳体预制体上的流动特征。研究结果表明:树脂在三维壳体预制体中流动时,流动前沿仍会出现半饱和区域;树脂流动前沿到达不同位置时,可以看出整个预制体内压力分布情况,压力先急速下降、后趋于平缓。填充初始时,压力下降很快,压力梯度很大,随着填充过程的进行,压力下降减慢且压力梯度减小。     

双流线型单叶片绕流流场的数值模拟

提出了一种新型水动能利用的垂直轴水轮机,选用半椭圆+圆弧流线型和Clark Y翼型作为叶片的基本结构,构建了一种可在水电站出水口利用水动能的双流线型自动开合式水轮机,分析了不同湍流模型下水轮机单叶片的绕流流场形态,探究了单叶片水轮机的运行状况。结果表明,标准k-ε模型更适用于双流线型叶片的模拟。除此之外,单叶片在0°～90°及270°～360°均为负转距,无法使水轮机正常运转,应采用多组叶片的结构来消除负转距的影响,以提高水轮机效率。     

基于欧拉方法的机翼表面水滴撞击特性数值模拟

基于欧拉方法分析了不同飞行速度和不同气象条件下NACA0012机翼水滴撞击的特性,使用Fluent商用软件计算空气流场,并通过UDS模块求解水滴相控制方程。从计算结果分析得出:局部水滴收集系数及水滴撞击范围随飞行速度和平均水滴容积直径的增加而明显增加;液态水含量对水滴撞击特性影响不大。     

量子高密度编码原理及其MATLAB仿真

由于没有实际操纵量子比特的条件,MATLAB以其简便的矩阵操纵手段和强大的科学计算功能,成为通信工程人员和在校学生学习量子通信基本原理的良好工具。给出了量子比特及其测定、量子序列、贝尔态基和常用量子逻辑门的MATLAB语言描述。分析了量子高密度编码原理,给出了MATLAB仿真程序。     

Numerical simulation of wind flow fields around buildings using the lattice Boltzmann method

This paper presents the simulation results of the wind environment around a single high-rise building and that around two tall buildings in tandem arrangement by using the lattice Boltzmann method with an aim to understand the ventilation issues around high-rise buildings in an urban environment. We analyzed the velocity distribution around the buildings and performed numericl simulations to reveal the formation and evolution law of the complex vortex system around the high-rise buildings. Numerical simulation results manifest a periodicity phenamenon in the process of the vortex evolution. For the case of two high-rise buildings, wind velocity in the space between the two buildings is very small, which is nearly a silent regime. Wind velocity above the front building is relatively larger and the maximum wind velocity is approximately 2.5 times the incoming wind velocity. The numerical results can be used in layout planning of high-rise residential buildings to create better environment for ventilation purpose in an urban area.     

平原河网地区桥渡壅水平面二维水流数值模拟

为分析平原河网地区桥渡对桥址河段壅水及流速场变化的影响,以杭州市德胜快速路石德立交R4匝道跨备塘河桥为例,根据实测河道水下地形资料进行网格概化,以上塘河流域MIKE11一维水动力模型计算成果作为控制边界条件,利用MIKE21建立了平面二维桥渡数学模型。结果表明,遭遇20年一遇洪水时,桥墩上游一定范围内出现水位雍高,3个桥墩所在断面最大壅水高度达0.04m,最大壅水长度160m;桥墩附近的水流流向发生了改变,流速有所增大,对河道堤防和河床产生明显冲刷。该方法可在平原河网地区桥梁防洪影响分析工作中推广应用。     

两体碰撞的模拟实验探究

根据力学中两体碰撞的基本理论建立模拟实验的虚拟环境,利用坐标变换实现一般情况下两体碰撞问题的应用程序设计,建立起模拟实验的运行测试平台,通过对输入量和测试量的设置,能够定量描写和测试两体碰撞的各种情况,有效揭示两体碰撞问题的物理规律性。     

自适应双向快速密集树避碰运动规划算法

针对采样运动规划算法效率低,尤其在处理高维空间和复杂障碍环境等问题时,严重依赖于所选采样参数和碰撞检测距离等,提出了一种自适应双向快速密集树（ABiRDT）避碰运动规划方法。首先,深入研究了ABiRDT算法的基础理论和实现方法,可适应调整碰撞检测距离参数和随机采样扩展步长;其次,重点研究了本算法所采用的c-空间加权均匀采样、最近邻位形查找和基于混合包围盒的并行离散碰撞检测等关键自适应策略;最后,通过三维可视化计算机仿真验证了本文提出算法的有效性。     

Numerical simulation and experimental investigation of 3-D separated flow field around a blunt body

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十字型网状结构在泥石流块石冲击下的动力响应数值模拟

针对柔性网变形性好和钢管混凝土抗冲击性能良好的优点,提出十字型网状结构,用来抗击泥石流灾害中的块石冲击。利用有限元软件ANSYS LS-DYNA进行数值模拟,得到结构在不同冲击速度、不同冲击网直径、不同冲击物质量和不同冲击高度条件下的动力响应。结果表明:1)相同冲击速度下,随着冲击网直径的增大,结构的刚度增加,其动力响应中的冲击力峰值增大;反之,减小。2)相同冲击速度和冲击物质量条件下,随着冲击网直径的增大,冲击点处的位移峰值降低,降幅在10%左右。3)相同冲击网直径下,随着冲击物质量的增加,冲击力峰值增大;随着冲击高度的增加,冲击力峰值减小。综上所述,冲击速度、冲击网直径、冲击物质量和冲击高度影响十字型网状结构的抗冲击性能。     

超声波地层解堵模拟计算

研究利用超声波辐射解除多孔介质中的堵塞微粒,模拟微观条件,计算在地层堵塞中微粒的受力情况,由各种情况下微粒脱落的条件,得出超声波在一定频率下所需声强大小.     

热学参数对裂隙岩体水流-传热温度影响的数值分析

针对裂隙岩体概念模型,采用3DEC离散元模拟计算不同热学参数下裂隙岩体的温度场和裂隙出水口水温变化。结果表明:1)岩石热传导与裂隙V_1水流约在热源放热2.5 d后开始耦合,裂隙V_2约在热源放热5 d后开始耦合。模型达到稳态时,由于裂隙V_1更加靠近热源,裂隙V_1比V_2水温高约10℃。2)由于裂隙水流动传热作用,使模型下端温度高于上端,岩体等温线形成从左向右的温度梯度。3)模型达到稳态时,岩石的比热增大200 J/(kg·℃)时,岩体温度降低约1℃;岩石的导热系数增大0.5 W/(m·℃)时,岩体温度升高约3℃;水的比热增大0.8 J/(kg·℃)时,岩体温度降低约2℃;水的导热系数增大0.05 W/(m·℃)时,岩体温度降低约0.001℃;岩石与水的对流换热系数增大5 W/(m~2·℃)时,岩体温度降低约1℃。模型达到稳态所需时间随各参数的增大而缩短。