聚合物溶液在波纹管中的流动特性

本文研究了聚合物驱中聚合物溶液流动的现状、多孔介质模型、粘弹性流体模型,波纹管模型的状况。选择适当的粘弹流体模型,简化油藏多孔介质模型,波纹管模型,建立了由连续方程,运动方程和上随体Maxwell本构方程,流函数,涡量函数及边界条件组成的较完整的数学模型。得到了在波纹管条件下的流函数场,速度场,应力场。其结果与文献中所做的图形对比发现结果吻合的较好,为在理论上研究粘弹性聚合物溶液的驱油机理做出帮助。     

塑料熔体三维流动的数值模拟

塑料熔体是具有记忆性的非线性黏弹性流体，为了准确分析板材挤出模具中熔体的流动，采用了积分型本构方程描述熔体的流变行为，同时给出熔体在狭缝流道中的控制方程。根据控制方程的特殊性，提出了把有限元半解析法应用于求解黏弹性流体流动问题这一思想，从而建立了有限单元体法，同时给出求解非线性有限元方程组的迭代方法，并采用以上方法对熔体在狭缝流道中的流动进行求解分析，将结果与三维有限元解法的结果相比较，证明结果是精确的，表明采用上述方法模拟熔体在狭缝中的流动是简便可行的。     

聚合物流动的多尺度模拟

基于聚合物分子运动论,提出了一种新的计算聚合物流体的多尺度方法。该方法在宏观尺度上应用无网格方法求解速度场,在微观尺度上应用随机模拟技术计算聚合物对应力的贡献,从而避免需要本构方程来封闭连续性方程和动量守恒方程。对Hooke哑铃模型、FENE哑铃模型、FENE-P哑铃模型,模拟了突然起动平面Couette流动;对Hooke哑铃模型,模拟了方腔驱动流动。从而验证了该方法的有效性和计算结果的可靠性。     

聚合物熔体矩形流道挤出胀大的数值模拟

运用Picard迭代格式的有限元方法,采用Wagner积分型本构方程对黏弹流体挤出胀大进行三维模拟分析。每次迭代根据新的自由面边界位置重新划分网格,由前一次迭代得到的速度场,算出单元高斯点流线,沿流线积分计算应力,把应力作为拟体力,建立非线性方程组迭代格式。对不同宽度和长度的矩形流道的挤出胀大进行模拟计算,分析了流道宽度和长度对胀大率的影响,结果表明,随着宽厚比的增加,厚度胀大率随之增加,随着流道长度的增加,胀大率逐渐下降。并把结果与二维狭缝流道的数值模拟和实验结果相比较, 结果表明,用该方法对黏弹流体挤出胀大流动进行三维模拟是可行的和准确的。     

非牛顿流体搅拌流场的数值模拟研究进展

对非牛顿流体搅拌流场数值模拟过程中的控制方程、旋转桨叶的处理以及数值计算方法三个方面进行了综合论述。阐述了广义牛顿流体模型形式简单、计算量低,在非牛顿流体搅拌流场数值模拟过程中应用广泛;黏弹性流体本构方程具有高度的非线性,采用计算流体力学(CFD)方法对其搅拌流场进行数值模拟难度较高,目前仍处于起步阶段;通过合理简化黏弹性流体本构方程以及采用恰当的数值离散方法,有助于在黏弹性流体的搅拌流场数值模拟中取得进展。     

用Navier-Stokes运动方程求解环形流道中的变质量流动

流体在环形流道中作变质量流动是一个特殊条件下的二维变质量流动问题,本文用Navier-Stokes运动方程和连续性运动微分方程,求解这种流体流动的静压变化规律,导出了有实用价值的计算公式,并由此式求得一维变质量流动时流道中静压变化的计算公式,所得之计算式与由动量守恒原理导出的公式完全一致。     

三维注射成型流动模拟的研究

介绍了一种基于三维模型的注射成型流动模拟的数学模型和数值实现，把速度和压力同次插值方法成功地应用到三维注塑模拟的计算中，从离散的动量方程中找出压力和速度的关系，然后代到连续性方程中得到压力方程。用三维控制体积法追踪流动前沿，并通过算例分析来说明三维模型的有效性。     

聚合物熔体全三维非等温数值模拟

采用基于交错网格的有限体积法(FVM)离散了4大方程,给出了能量方程的全三维离散格式。运用SIMPLE算法求解了矩形截面流道内熔体的速度场和压力场,通过耦合动量方程和能量方程,进而得到整个机头流道内温度的分布。计算中采用了Carreau流变模型,并给出了作为温度函数的流动指数n的解析表达式。模拟结果表明:在入口区,熔体从近壁面区域向流道的中心区域汇集,进入全展流区后,熔体的流场不再变化;熔体内温度分布较为复杂,影响因素众多。     

列管反应器中环形分布器内流体均布的探讨

利用动量守恒原理,推导出列管反应器中环形分布器内流体流动的修正动量方程,并在与前人实验结果比较和分析的基础上,提出了与环形分布管相适应的分流和合流动量交换系数式。研究结果表明,环形分布器内流体流动符合变质量流动规律,可采用环形分布器修正动量方程描述分流和集流的静压变化;通过直管分布器实验获得的动量交换系数对环形流道分布器也是适用的,其计算值与实验值的相对误差小于10%,可满足工程设计要求。     

注塑成型充填过程的可压缩流动分析

注塑成型过程中,熔体在型腔中的流动和传热对制品质量性能有重要的影响.为了预测注塑制品的收缩、翘曲和力学性能,精确预测充填过程的流动及传热历史是十分必要的.本文考虑熔体的可压缩性及相变的影响,将充填过程中熔体的流动视为非牛顿可压流体在非等温状态下的广义Hele-Shaw流动.采用有限元/有限差分混合方法求解压力场和温度场,采用控制体积法跟踪熔体流动前沿,并应用Visual C++实现了注塑充填过程的可压缩流动分析.为了保证能量方程各项在单元内边界的连续性,结点能量方程各项由单元形心处的离散值加权平均获得,因而,能量方程在计算区域内整体求解.对两个算例进行了分析,模拟结果与实验结果的对比,验证了本文数值算法及程序.     

Multiscale fluid transport theory for swelling biopolymers

Fluid flow through a (bio) polymeric matrix has multiscale characteristics and is affected by the relaxation of surrounding polymers. Models developed in the past were either single scale (Polymer (1982) 23 (4) 529; Chemical Engineering Science (1992) 47 (12) 3037) or were limited to systems with a short memory (Achanta, 1995; Moisture transport in shrinking gels during drying, Ph.D. thesis, Purdue University, West Lafayette, IN). To address these limitations, we use the generalized Darcy's law equations of Singh (Effect of viscoelastic relaxation on fluid and species transport in biopolymeric materials, Ph.D. thesis) and the mass balance equations of Bennethum and Cushman (International Journal of Engineering Science (1996) 34 (2) 125) to develop a multiscale fluid transport model. The effect of viscoelastic relaxation of solid polymers on the flow of vicinal (adsorbed) fluid is considered at the mesoscale. At the macroscale two bulk fluids are incorporated, one of which is identical to the vicinal fluid. The mass balance equations for the vicinal fluid and its bulk counterpart are coupled via source/sink terms. The resulting fluid transport equation includes a novel integral term related to viscoelastic properties of the biopolymeric matrix. This term incorporates viscoelastic effects with both short and long memory. The model can describe both Darcian (Fickian) and non-Darcian (non-Fickian) modes of fluid transport. The model suggests fluid transport is Darcian in the rubbery and glassy states when the biopolymers are sufficiently far from the glass transition region. In the proximity of glass transition the flow of fluids is anomalous or non-Darcian. These predictions are in agreement with the experimental observations of Kim et al. (Chemical Engineering Science (1996) 51 (21) 4827). In spite of its multiscale characteristics, the resulting transport equation is simple and can be easily solved. The experimental parameters needed to solve the equation are the effective diffusivity, a sorption or drying curve and viscoelastic properties of the material.     

Decomposition of three-dimensional linearized equations for Maxwell and Oldroyd viscoelastic fluids and their generalizations

A new exact method of solving general three-dimensional nonstationary linearized equations for viscoelastic fluids is described based on breaking these equations down into several simpler equations. Formulas are given that make it possible to express the solution in the respective systems (consisting of four connected equations) by solving two independent equations. The most widespread rheological models of viscoelastic fluids are considered to illustrate the powerful capabilities of the proposed method. A new differential-difference model for a viscous fluid with a constant relaxation time is proposed that gives a finite disturbance propagation rate and is in good agreement with the Maxwell and Oldroyd differential models of viscoelastic fluids. The axial flows of viscoelastic fluids are studied, and solutions to certain hydrodynamic problems are given.     

塑料挤出吹塑中型坯成型模拟采用的本构方程

型坯成型是塑料挤出吹塑中的一个重要阶段。对型坯成型阶段的数值模拟可分为两种方法：一种是将型坯机头内的聚合物熔体看作牛顿流体，另一种是将其看作粘弹性流体。在对粘弹性流体进行分析时，用到了微分型和积分型的本构方程，对此进行了较系统的介绍。     

挤出吹塑的型坯成型研究中的本构方程

型坯成型是挤出吹塑中的一个重要阶段。对型坯成型阶段的数值模拟可分为两种方法:一种是将机头内的聚合物熔体看作牛顿流体;另一种是将其看作粘弹性流体。在对粘弹性流体进行分析时,用到了微分型的和积分型的本构方程。     

Modelling the bubble formation dynamics in non-Newtonian fluids

A theoretical model is developed for modelling the non-spherical bubble formation at an orifice submerged in non-Newtonian fluids under constant flowrate conditions. The equations of motion are, respectively, the radial expansion and vertical ascension of the bubble interface. They are combined with the thermodynamic equations for the gas in the bubble and the chamber below the orifice as well as the fluid rheological equation. In particular, the influence of in-line interactions between bubbles due to the fluid memory effects of the viscoelastic characteristics is taken into account for the first time. The present model is able to compute the instantaneous growing shape of the bubble during its formation and determine the final size of detachment as well as the frequency of bubble formation. The values predicted by this model compare satisfactorily with the experimental results obtained under different operating conditions.     

UNSTEADY ANALYSIS OF VISCOELASTIC BLOOD FLOW THROUGH ARTERIAL STENOSIS

A mathematical model of unsteady non-Newtonian blood flow in an artery under stenotic condition has been developed. The flowing blood is considered to be a viscoelastic fluid characterized by the Oldroyd-B model and the arterial wall is considered to be rigid, having cosine-shaped stenosis. The governing equations of motion accompanied by appropriate choice of the initial and boundary conditions are solved numerically by the MAC (marker and cell) method, and the results are checked, for numerical stability with desired degree of accuracy. The key factors like the wall shear stress, resistive impedance, and the other viscoelastic parameters are also examined for further qualitative insight into the flow through arterial stenosis. Comparison of the results reveals that dimensionless pressure drop for the viscoelastic model increases while it diminishes for the shear-thinning power law model over that of the Newtonian model. Moreover, the possibility of flow separation increases with increasing relaxation time (Deborah number), and in case of Newtonian fluid, delayed separation is observed. The grid independence study has also been performed successfully in order to validate the applicability of the methodology as well as the model used under consideration. Special emphasis has duly been made to compare the present theoretical results with the existing ones, and good agreement between them has been achieved both qualitatively and quantitatively.     

锚式搅拌槽中高粘弹性流体的流速分布及其功率消耗

用照相法测定了锚式搅拌槽中高粘弹性流体的流型和流速分布,另测定了搅拌功率消耗,结果发现:1.与牛顿流体相比,在低Re数下,粘弹性流体的切向速度较大,而径向速度则较小.2.转速相同时,在高剪切率区域,粘弹性流体的剪切率大于牛顿流体.由CEF方程导出功率计算式N_pRe_af_s~(1-n)=k_pf_vf_s~2[1+F_1avf_s~(m-n-3)Wi/K_s~2]用实验数据确定f_(?)和F_(1av),得到可适用于牛顿流体、假塑性流体和粘弹性流体的普适功率计算式,计算结果与实验值比较接近.     

Robust Direct Numerical Simulation of Viscoelastic Flows

Many technical processes involve viscoelastic flows, which makes the subject interesting for CFD. Despite the complex fluid rheology and related numerical problems in solving the constitutive equations, recent stabilization approaches allow for a robust simulation of viscoelastic flows in the technical relevant range at high degrees of fluid elasticity. A recent general‐purpose numerical stabilization framework, based on the finite‐volume method of OpenFOAM is presented and its capability for the robust simulation of viscoelastic single‐, as well as two‐phase flows is shown.     

A MODEL FOR STRUCTURED FLUIDS

Steady-state and time-dependent non-Newtonian properties of structurally complex systems, such as suspensions and foodstuffs, are simulated by the extension of a recently developed fluid model. This model accommodates the concept of structure variation induced by flow via a kinetic approach similar to the treatment of reversible chemical reactions. Purely viscous and viscoelastic responses are considered, entailing different equations for the computation of their contribution to the overall stress sustained by the systems. The model successfully describes pseudoplastic and thixotropic behavior, with or without yield stress.