非牛顿流体在Hele-Shaw模型中的流动

本文研究了非牛顿流体在Hele-Shaw模型中的流动特性,并用摄动法求出了Bingham流体、Power-law流体的速度分布、压力降与流量的关系,分析了屈服应力及幂律指数对物理参数的影响.     

非稳态分数阶Oldroyd-B流体绕楔形体流动研究

研究了非稳态分数阶Oldroyd-B流体在多孔介质中通过楔形拉伸板的驻点流动问题。基于分数阶Oldroyd-B流体的本构模型建立了动量方程,并在其中引入了浮升力和驻点流动特征。此外,考虑了具有热松弛延迟时间的修正的分数阶Fourier定律,并将其应用于能量方程和对流换热边界条件。接着,采用与L1算法相结合的有限差分法求解控制偏微分方程。最后,分析了相关物理参数对流动的影响。结果表明,随着楔角参数的增加,流体受到的浮升力增大,导致速度加快;达西数越大,介质的孔隙度变大,流体的流动越快;此外,温度分布先略有上升后明显下降,这表明Oldroyd-B流体具有热延迟特性。     

非等温黏弹性复杂流动的改进SPH方法模拟

非等温黏弹性流体广泛存在于自然界和工业生产中,准确预测黏弹性流体的非等温流动机理和复杂流变特性有着重要的应用价值.文章提出一种改进的光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法对非等温黏弹性复杂流动进行了数值模拟,其中流体的黏弹特性通过eXtended Pom-Pom本构模型来表征.为了提高模拟结果的精度,采用了一种核函数梯度的修正算法;为了灵活地施加边界条件,发展了边界粒子和虚拟粒子相联合的边界处理方法;为了消除流动过程中的拉伸不稳定性,施加了粒子迁移技术.运用改进SPH方法数值模拟了液滴撞击固壁和F型腔注塑成型问题,通过与Basilisk软件得到的结果进行比较验证了改进SPH方法求解非等温黏弹性流体的有效性.通过利用不同粒子初始间距进行计算,评价了改进SPH方法的数值收敛性.研究了非等温流动相较于等温流动的不同流动特征,深入分析了不同热流变参数对流动过程的影响.数值结果表明,文章提出的改进SPH方法可稳定、准确地描述非等温黏弹性复杂流动的传热机理、复杂流变特性和自由面变化特性.     

一种修正的低温流体空化流动计算模型

为了更准确地预测低温流体的空化流动特性, 基于Kubota空化模型, 对蒸发和凝结源项进行修正, 建立了一种考虑热力学效应的空化模型. 分别采用原始和修正的Kubota空化模型, 计算了绕对称回转体液氮的空化流动, 通过与实验结果的比较对修正的空化模型进行了评价. 结果表明, 与原Kubota空化模型比较, 修正的空化模型由于考虑了热力学效应, 计算获得的蒸发量减小, 凝结量增大, 空穴长度减小, 空穴界面形态呈模糊状态.计算结果与实验结果更加一致, 说明修正的空化模型能准确的描述低温流体空化过程的质量传输过程, 能够更准确模拟低温流体中的空化流动特性.     

串列双方柱体流体动力载荷研究

本文通过流动显示,热线测频和流体动载荷测量在水槽中研究了绕经不同柱间距比S/D(S为双柱间距,D为柱体截面宽)串列双方柱体流动特性。实验雷诺数为Re=6×10~3,柱间距比0.5≤S/D≤10实验测量了涡脱落频率、时间平均阻力、动态阻力和动态升力。通过实验结果综合分析给出临界柱间距范围2.5≤(S/D)_(cr)≤3.0,并将串列双方柱流动随柱间距的变化划分为二种流态区。在临界柱间距,作用于双柱体的流体载荷、涡脱落频率以及流谱都发生跃变。文中分析讨论了两个流态区的特性以及在临界柱间距出现的双稳态特性。     

纤维悬浮液搅拌流动的数值模拟

由于缺乏适当的本构方程，对纤维悬浮液流动的研究一直局限于纤维的牛顿流体悬浮液。本文采用ＭＵＣＭ模型对作者最近提出的纤维Ｏｌｄｒｏｙｄ－Ｂ流体悬浮液的本构方程作了改进，并对锚式桨搅拌槽的二维Ｏｌｄｒｏｙｄ－Ｂ流体和牛顿流体纤维悬浮液搅拌流动作了数值模拟。模拟的结果表明，本文所用的模型和方法能有效地抑制过大局部应力的影响并合理地处理流体的记忆效应。     

液浮转子微陀螺筒间流动阻力矩参数影响

建立简化计算模型,将一种具有空间指数收敛特性的谱元-Fourier法引入复杂的液浮转子微陀螺筒间流动的直接数值模拟。对于柱坐标系下不可压缩Navier-Stokes方程,在子午面的径向和轴向采用Galerkin谱元法,进行标准化的Gauss-Lobatto-Legendre节点展开,在周向采用Fourier级数展开法。设定基准算例,计算分析了高径比、旋转速度和黏性系数等参数对内筒侧面和内筒端面阻力矩的影响。结果表明,两种阻力矩都随这些参数的增大而增大,且对总阻力矩的贡献量级相当。     

Casson流体在旋转圆盘上的流动

本文研究Casson流体在旋转圆盘上的涂层流动特性,得到基本流动的速度分布,并且用Runge-Kutta法进行数值计算,得到薄膜厚度随时间和流态参数的变化规律,还用能量法检验了流动稳定性。     

共转Oldroyd B流体剪切-拉伸流动研究

应用宏观理论的共转模型研究纺丝拉伸过程中测粘-拉伸流动的流变学，以探讨液晶高分子流体纺丝拉伸初步机制。由共转Oldroyd B流体模型的本构方程导出了测粘-拉伸流动的法向应力差和拉伸粘度的解析表达式，利用边界条件及运动方程列出了主拉伸速度与纺程的微分方程。应用Matlab软件绘制出拉伸粘度和主拉伸速度随其它参数变化的曲线，从而得到这些参数对纺丝拉伸流动流变学性能的影响，这对纺丝过程的工艺控制有一定的指导意义。     

穿孔壁面通道流动阻力特性研究

利用计算流体力学方法对穿孔壁面通道内部流动进行了数值模拟,分析了其流动沿程摩擦阻力特性。计算中,假设流体不通过小孔进出穿孔壁面背后的吸声材料。经实验对比,采用Realizable k-ε湍流模型结合增强型壁面函数,可获得比较理想的计算结果,数值模拟与实验测量的压损值相对偏差在10%以内。对于穿孔壁面通道流动阻力计算,提出了等效粗糙度概念,结合达西公式、克罗布鲁克公式计算获得了等效粗糙度数值。研究了穿孔板小孔孔径、穿孔率对等效粗糙度的影响,发现等效粗糙度与孔径成二次方关系、与穿孔率成线性关系。     

Nonlinear stability of truncated shallow conical sandwich shell with variable thickness

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夹层扁球壳的非线性稳定性

基于Reissner假设和变分原理,给出夹层扁球壳在均布压力作用下的大挠度方程,采用修正迭代法求得了夹层扁球壳非线性稳定问题的解析解,得到两类边界条件下临界屈曲载荷的表达式,讨论了几何参数和物理参数对临界屈曲载荷的影响     

The effective homogeneous behavior of heterogeneous porous media

The macroscopic equations that govern the processes of one- and two-phase flow through heterogeneous porous media are derived by using the method of multiple scales. The resulting equations are mathematically similar to the point equations, with the fundamental difference that the local permeabilities are replaced by effective parameters. The method allows the determination of these parameters from a knowledge of the geometrical structure of the medium and its heterogeneities. The technique is applied to determine the effective parameters for one- and two-phase flows through heterogeneous porous media made up of two homogeneous porous media.     

Application of the modified iteration method to nonlinear vibration of corrugated circular plates

In this paper, the modified iteration method is successfully extended to investigate the nonlinear free vibration of corrugated circular plates with full corrugations. The analytical relation for the amplitude-frequency response of corrugated circular plates is obtained and discussions on the influences of geometrical parameters on vibration behaviours of corrugated circular plates are made. The present results are practically important in the design of elastic elements in precision instruments.     

Supersonic flow of a rarefied gas around a wire grid

The direct simulation Monte Carlo method is used to study a plane-parallel supersonic gas flow through a grid formed by a number of infinite parallel wires. Characteristic features of the shock disturbance formation of in the interaction of a supersonic flow with a permeable grid are revealed. Particular attention is paid to studying the influence of geometrical parameters of the wire target on the number of particles colliding with the surface of the wires.     

Numerical study on mitigating severe slugging in pipeline/riser system with wavy pipe

The gas/liquid two-phase flow in pipeline/wavy-pipe/riser systems was investigated numerically with CFD. A CFD model of the pipeline/wavy-pipe/riser system was obtained by adding a wavy pipe to the model of the pipeline/riser system verified by the experimental data previously. The effects of the geometrical parameters and location of the wavy pipe on its performance of slug mitigation and flow characteristics in pipeline/wavy-pipe/riser systems were examined through the CFD models. With the increase of the amplitude or length of the wavy pipe, the slug in the pipeline/riser system becomes shorter. The optimum location of the wavy pipe in the pipeline exists for a pipeline/riser system and a wavy pipe at given operating conditions. The CFD modelling provides a feasible and flexible way to investigate the effectiveness of the wavy pipes on mitigating severe slugging in pipeline/riser systems.     

An experimental investigation of the flow about a sphere rotating in a rivlin-ericksen fluid

Tangential and radial velocity profiles were measured for the flow about a sphere rotating slowly in a Newtonian fluid, contained in a rectangular tank. Velocities were determined from enlarged streak photographs of aluminium particles moving in a collimated “sheet” of light, at several planes through the flow field. Similar velocity profiles were measured for the flow of a 1.50% Natrosol 250 H solution about two spheres of different diameters rotating in two different sized rectangular tanks. A set of velocity distributions were also measured for a sphere rotating in a 0.9% Natrosol 250 H solution. A dye tracer study of the flow about a sphere rotating in this liquid is presented as well. Both Natrosol solutions exhibited viscoelastic behaviour. The Newtonian fluid study was carried out at a Reynolds number of 1.2 and the viscoelastic fluid studies were within the Reynolds number range of 0.05–1.24.The zero shear viscosities of the Natrosol solutions were measured using the falling-sphere method. The non-Newtonian material parameters were obtained by fitting the theoretical curves to the measured velocity data. The values of the elastic and shear thinning parameters for the two liquids obtained in the different geometrical and dynamical situations are compared.     

平流层飞艇绕流场与柔性变形的数值模拟

处于平流层流场中的飞艇,其整体刚度较小,为柔性体,可视为弹性薄膜结构,外围的流场的状态分布与其形状有着密切的关系,从本质上说是一个流固耦合问题。本论文以此为背景,分析了平流层飞艇的外围流场与柔性蒙皮变形的非动态耦合关系。我们采用叠代计算方法来处理这一问题,其中飞艇的三维流场的计算本文采用基于有限体积法的压力修正SIMPLE算法,而飞艇弹性变形的数值模拟计算应用了薄壳无矩理论。本文比较了气动弹性变形和静态超压变形两种不同情况下的飞艇流场压力分布以及气动参数,分析了飞艇变形与流动参数、气动荷载变化的关系。     

喷嘴结构对液氧煤油火箭发动机高频燃烧不稳定性的影响

为了筛选高压补燃循环液氧煤油火箭发动机的喷嘴,在喷注单元低压高频燃烧不稳定性模拟实验系统上开展实验,研究了喷嘴结构对燃烧稳定性边界的影响。实验使用气态空气与氧气的混合物作为氧化剂,加热的煤油蒸汽作为燃料;喷嘴为全尺寸气液同轴直流离心式喷嘴,模拟燃烧室与真实燃烧室的固有声学频率相等。根据测量模拟燃烧室内的脉动压力区分大幅振荡、小幅振荡和稳定工作。研究结果表明,喷嘴长度、缩进室长度和入口节流嘴直径对高频燃烧不稳定性裕量有很大影响,并存在相对最佳值。