两相流动中椭圆颗粒沉降规律的数值模拟

应用任意拉格朗日-欧拉(ALE)算法,对椭圆形颗粒在一定雷诺数范围内的沉降过程进行了数值模拟,流体运动由守恒方程计算,通过积分黏性应力和压力获得的颗粒受力来跟踪颗粒运动.结果表明:圆形颗粒与初始时刻长轴垂直于x轴放置的椭圆颗粒,一直沿通道中心线稳定沉降;初始时刻长轴平行于x轴放置的椭圆颗粒,沉降时向一侧壁面旋转靠近,最终也稳定在通道中心线,颗粒长轴与颗粒沉降方向垂直;两种情况下的椭圆颗粒最终沉降速度相同.     

基于非结构化网格和浸入边界的流固耦合数值模拟

对浸入边界方法进行改进,使其适用于非结构网格。利用非结构化网格技术生成贴体网格,充分利用贴体网格与浸入边界的优势,提高复杂区域内流固耦合问题计算效率。流体Navier-Stokes方程空间项采用非结构化网格有限体积法离散,时间项采用欧拉隐式方法。利用浸入边界方法模拟运动固体区域,流固界面作用力通过VOS(Volume Of Solid)方法进行处理。通过振荡圆柱绕流计算结果与文献实验数据对比,验证了本文方法的合理性和正确性,利用本文方法对管路中阀门动态过程进行了数值研究。     

基于有限体积法的三维CFD-DEM耦合方法

本文基于有限单元法对流体控制方程进行离散,并与离散单元法进行三维流固耦合计算。首先,针对多孔介质土体选取合适的控制方程,包括流体运动方程、颗粒运动方程及流固相互作用方程。然后将编译的计算流体力学程序引入离散单元法中进行耦合计算。最后,针对单颗粒沉降进行了数值模拟,结果表明:颗粒在刚开始下落时,速度增加较快,然后增加速率逐渐变缓并趋于稳定;随着颗粒的不断下降,其所受拖拽力随着时间先迅速增加,然后逐渐与浮重力一致;颗粒下降速度稳定后,水压(扣除静水压力)在颗粒附近呈蝶翼状分布,且颗粒上方为负压,下方为正压;颗粒下方水流向两侧外流,而上方水流向颗粒上方汇聚。以上研究结果表明此次编译的计算流体力学程序能够很好地和离散单元法进行耦合,并可用于研究多孔介质流固耦合问题。     

水涡轮机械中的湍流固－液两相流动及磨损研究

导出了固体颗粒在任意流场中运动的Ｌａｇｒａｎｇｉａｎ方程，对此方程进行线性化，并求出了其颗粒运动方程的解析通解。使用颗粒运动方程数值求解和分析了稀疏颗粒湍流场中固体颗粒的运动。建立了湍流固－液两相流的Ｋ－ε双方程湍流模型、体积分数湍流模型、Ｅｕｎｌｅｒｉａｎ－Ｌａｇｒａｎｓｉａｎ混合湍流模型以及颗粒磨损模型，利用这些模型对一些水涡轮机械过流通道内的流动及固壁磨损进行了数值模拟，其预测结果与实验结果较为一致     

水涡轮机械中的湍流固—液两相流动及磨损研究

导出了固体颗粒在任意流场中运动的Ｌａｇｒａｎｇｉａｎ方程对此方程进行线性化，并求出了其颗粒运动方程的解析通解。使用颗粒运动方程数值求解和分析稀疏颗粒湍流场中固体颗粒的运动。建立了湍流固－液两相液的Ｋ－ε双方湍流模型，体积分数流模型，Ｅｕｎｌｅｒｉａｎ－Ｌａｇｒａｎｇｉａｎ混合湍流模型以及颗粒磨损模型，利用这些模型对一些水涡轮机械过流通道内的流动及固壁磨损进行了模拟，其预测结果与实验结果较为一致。     

求解流体与结构相互作用问题的ALE有限体积方法

本文发展了求解流体与结构相互作用问题的数值方法。采用任意拉格朗日－欧拉网格（ＡＬＥ）和有限体积方法对流体的控制方程进行空间离散，而时间项则采用三点向后差分格式；对于结构的运动方程采用Ｎｅｗｍａｒｋ积分法进行求解，为了求解耦合的流体和结构的运动方程，采用预测－多步校正法以避免反复迭代所导致的过大的计算量。作为本入方法的应用，计算了圆筒内一同轴圆柱的自由振动问题，在小振幅的情形下，将由计算获得的附加质     

多相流中双球泡的动力学方程

建立了稀疏固－液两相流中双球泡泡壁运动的动力学方程，通过数值计算分析了球泡间以及固体颗粒与球泡间的相互作用，并考虑了可压缩性对双球泡溃灭的影响，以及液体与固体颗粒间阻力耦合作用的影响。     

模拟波浪运动的三维自由表面流动数值模型

基于Navier-Stokes方程建立了三维自由表面流动数值模型来模拟波浪运动.模型中Navier-Stokes方程的求解采用两步投影法,计算域的空间离散采用交错网格.采用满足自由表面运动学边界条件的水位控制方程来计算自由表面.通过数值结果与解析解的比较,验证了本文建立的三维自由表面流动数学模型可以精确的模拟线性色散波以及孤立波沿平底坡和非平底坡的传播.     

固液两相流中固体颗粒的垂直分选模型

在单个固相颗粒运动方程的基础上，进一步考虑了多颗粒条件下的颗粒之间的相互作用，并通过对液体流动特性的简化考虑，建立了固体颗粒在水流中运动的垂直分选模型。本文提出的颗粒分选模型建立在细致分析两相流运动过程中颗粒受力特点的基础上，有助于对两相流运动和沉积的各个子过程进行深入的了解，可以模拟各种颗粒在固液两相流中的运动过程和最终状态，经过统计平均得出固相颗粒的运动和分选规律。     

密度线性分层环境下垂直贴壁异重流数值模拟

通过求解雷诺时均N S方程,应用考虑密度的物质输运模型模拟计算了密度分层环境下的垂向二维贴壁射流过程,采用数值模拟方法对异重流的演进过程、头部运动速度进行了研究,并根据计算结果分析了异重流的演进特征以及浮力系数对运动特征值的影响。模拟结果表明数值计算结果与试验结果吻合,说明该数值模型可以比较准确地模拟分层流体环境下异重流的演进过程。     

EXPERIMENTAL AND NUMERICAL INVESTIGATIONS ON SECONDARY FLOWS AND SEDIMENTATIONS BEHIND A SPUR DIKE

For a physical model of the approach navigation channel of Three Gorges Project(TGP), flow patterns around a non-submerged spur dike placed as a mountain in a long rectangular glass flume were experimentally investigated with and without “sucking-spouting” water respectively. Based on rigid lid assumption and Dynamic Smagorinsky Model, all these vortex flows around the spur dike were numerically simulated and analyzed, which probably affect the whole flow field and then probably lead to sedimentations for silt-laden two-phase flows. Meanwhile, silt-laden flows were also investigated experimentally. Both the secondary flow region and the silt sedimentations downstream of the spur dike decrease greatly with “sucking-spouting” water compared to those ones without “sucking-spouting” water. The Finite Volume Method (FVM) was used to discretize the governing equations together with a staggered grid system, where the second order difference is employed for the diffusion terms and the source terms while the upwind difference QUICK is used for the convection terms. The computational results are all in fairly good agreement with the experimental data.     

RECENT PROGRESS IN INCOMPRESSIBLE REYNOLDSAVERAGED NAVIER-STOKES SOLVERS

ＲＥＣＥＮＴＰＲＯＧＲＥＳＳＩＮＩＮＣＯＭＰＲＥＳＳＩＢＬＥＲＥＹＮＯＬＤＳＡＶＥＲＡＧＥＤＮＡＶＩＥＲ－ＳＴＯＫＥＳＳＯＬＶＥＲＳ￥Ｃ．Ｈ．Ｓｕｎｇ；Ｔ．Ｔ．Ｈｕａｎｇ（ＤａｖｉｄＴａｙｌｏｒＭｏｄｅｌＢａｓｉｎ，ＣＤ／ＮＳＷＣＢｅｔｈｅｓｄａ，Ｍ...     

重力场中的粒子在沉降过程中的捕捉和再分离过程

本文对重力场中的粒子在沉降过程中的捕捉和再分离过程进行了理论上的研究。为了数学上处理方便，考虑圆球粒子在黏性流体中作低雷诺数运动。使用调和函数和双调和函数在不同坐标系中的变换关系和作者提出的扩展的连续反射方法，根据Lamb给出的低雷诺数流动的基本解表达式和线性方程的叠加原理，本文构造出了围绕两个球形粒子流动的完全解和在准静态条件下沉降粒子所受到的水动力和力矩的精确解。结合刚体力学中处理约束问题的方法和摩擦理论使得本文理论上证实了界面摩擦力是Stokes方程对称性预测失效的原因，并且确定了运动粒子在界面上的两种运动类型（纯滚动及其滚动伴随滑动）和范围，从而这使得本文可以描述粒子在沉降讨程中的捕捉和再分离过程。     

通量差分分裂上风差分格式求解船舶粘性流动

本文阐述了采用人工可压缩方法计算不可压缩粘性流体的流动问题。对一般曲线坐标系下的流动控制方程采用了通量差分分裂上风差分格式和二阶中心差分格式离散。在隐式求解格式下，代数方程组用线松弛方法求解。本文计算了Ｍ维圆柱绕流和Ｗｉｇｌｅｙ船的绕流问题，计算结果同试验相当吻合，这说明本文所采用的方法是处理不可压缩流动的可靠方法。     

AN OPERATOR-SPLITTING ALGORITHM FOR ADVECTION-DIFFUSION-REACTION EQUATION

An operator-splitting algorithm for three-dimensional advection-diffusion-reactionequation is presented.The method of characteristics is adopted for the pure advection operator,the explicit difference scheme is used for diffusion,and a prediction-correction scheme is em-ployed for reaction.The condition for stability of the algorithm is analysed.Severall inear andnonlinear examples are illustrated to test the convergence and accuracy of the numerical proce-dure,and satisfactory agreements between computed and analytical solutions are achieved.Dueto its simplicity,stability,and validity for both one-and two-dimensional problems,the success-ful algorithm can be used to numerical simulations of viscous fluid flows,the transport of pollu-tants and sedimentations in reservoirs,lakes,rivers,estuaries and other environments,cooling-problems in heat or nuclear power plants,etc.     

A MULTIGRID-ACCELERATED THREE-DIMENSIONAL TRANSIENT-FLOW CODE AND ITS APPLICATION TO A NEW TEST PROBLEM

A multigrid-assisted solver for the three-dimensional time-dependent incompressible Navier-Stokes equations on graded Cartesian meshes is developed. The spatial accuracy is third-order for the convective terms and fourth-order for the viscous terms, and a fractional-step strategy ensures second-order time accuracy. To achieve good time-wise efficiency a multigrid technique is used to solve the highly time-consuming pressure-Poisson equation that requires to be solved at every time step. The speed-up achieved by multigrid is shown in tabular form. The performance and accuracy of the code are first ascertained by computing the flow in a single-sided lid-driven cubic cavity with good grid-economy and comparing the results available in the literature. The code, thus validated, is then applied to a new test problem we propose and various transient and asymptotically obtained steady-state results are presented. Given the care taken to establish the credibility of the code and the good spatio-temporal accuracy of the discretization, these results are accurate and may be used for ascertaining the performance of any computational algorithm applied to this test problem.     

二维非恒定粘性泥石流运动堆积的数值模拟

以结构二相流模型为基础,建立了二维粘性泥石流运动堆积的数学模型。模型采用三角网格的有限差分方法,具有计算效率高、边界处理精度高的优点。针对粘性泥石流运动速度快、龙头部位前缘坡度陡的特性,简述了计算中的动边界处理及泥石流停积条件的处理方法。以云南东川蒋家沟泥石流堆积试验为例,模拟了不同来流补给量下粘性泥石流的运动堆积过程。     

Numerical simulations of viscous flows around surface ship by level set method

Numerical simulations of viscous flows around surface ships by coupling the 3D incompressible RANS equations with level set method are presented in this paper. The finite difference method is used to discretize the RANS equations with turbulent model SST k − ω. The fully nonlinear boundary condition at the free surface is satisfied at each time step and the evolution of the free surface is achieved by using the level set method. The coupled solver is applied to a benchmark case of viscous flows around an advancing Wigley ship with various Froude numbers. The computational results are in excellent agreement with experimental data. The simulations reveal clearly the generation and evolution of bow and stern waves.

     

DIRECT NUMERICAL SIMULATIONS OF THE DYNAMICS OF PARTICLES WITH ARBITRARY SHAPES IN SHEAR FLOWS

A fluid-structure interaction method based on the arbitrary Lagrangian-Eulerian method and a dynamic mesh method was developed to simulate the dynamics of a rigid particle in shear flows. In the method, the governing equations for the fluid flow and particle motion were sequentially solved in a two-way coupling fashion. The mesh system was deformed or re-meshed by the dynamic mesh method. The method was employed to simulate the dynamics of a single particle suspended in a flow channel and the dynamics of the particle were studied. The simulation results show that the angular velocity is not only a function of the inclination angle, is but also influenced by the aspect ratio yielding a hysteresis, while the angular velocity obtained from the Keller-Scalak model is a function only of the inclination angle and does not show a hysteresis. The present simulations clearly demonstrate that the Fluid-Structure Interaction (FSI) module is very stable, accurate and robust.     

弯道水流的两步隐式算法研究

采用优于SIMPLEC算法的两步隐式解法求解二维曲线坐标系下的浅水方程,建立了二维弯道水流数学模型。对流项采用二阶精度的Roe格式离散;物理变量采用适体坐标系下的同位网格布置,网格界面流速由动量插值法计算;紊动黏性系数由修正的k-ε模型确定。采用此模型对弯道内的水流流动进行了数值模拟,计算结果和实测数据吻合较好。