凹槽模型中聚合物溶液微观渗流的有限体积方法

为了形成对粘弹性聚合物溶液在微观孔隙中流动行为的完整的数学描述,便于从理论上研究粘弹性流体的微观驱油效率,本文针对残余油的微观存在形式,使用了凹槽流道模型。并结合非线性上随体Maxwell本构方程,动量方程、连续性方程以及两种流道的边界条件,建立了完整的数学模型。采用有限体积法求解了由UCM本构方程、动量方程、连续性方程和流道的边界条件构成的非线性耦合方程组。为了解决流场计算中的一个关键问题,即不合理的压力场的检测,同时为了保证计算的准确度及对压力的物理特性模拟,本文对整个计算域采用交错网格,并且采用乘方格式对动量方程进行离散,从而得出控制方程组的离散方程式。本文选择交替方向隐式迭代法,并补以块修正技术以促进收敛,最后得到了粘弹性流体在收缩流道内流动时的速度场、流函数场。     

瞬态热传导方程的SPH法

光滑粒子流体动力学(Smooth Particle Hydrodynamics,SPH)作为一种无网格方法具有无网格、自适应性和拉格朗日性质。本文将SPH方法应用到瞬态热传导问题的求解,通过将二阶导瞬态热传导方程分解成两个一阶导的偏微分方程,同时对时间域进行离散,建立了基于SPH方法的瞬态热传导离散方程。通过镜像粒子法处理边界条件,提高了计算精度。对一维和二维瞬态热传导问题进行数值分析,采用lucy核函数和三次样条核函数进行求解,通过与精确解对比,验证了该方法的可行性和实用性。     

煤气化-无烟燃烧立式锅炉内空气动力场的数值模拟研究

采用RNGk ε湍流模型、其动量方程利用具有三阶精度的QUICK格式离散的方法 ,对一台采用了无烟燃烧技术的锅炉炉内冷态流场进行了数值模拟 ,并根据模拟结果对这一新技术进行了理论上的探讨     

闭式安全阀泄放管道瞬态不平衡力的数值分析

为研究闭式安全阀系统泄放过程中泄放管道内的瞬态不平衡力,建立了泄放管道的三维模型,并使用流体力学计算方法对泄放过程中管道内的瞬态流动进行了数值模拟。模拟结果显示了泄放管道内瞬态不平衡力的存在。峰值瞬态不平衡力与弯头间直管段的长度和动载因子有关,其在弯头间直管段的长度等于声波波长时达到最大,当弯头间直管段的长度小于声波波长时,峰值瞬态不平衡力与弯头间直管段的长度成正比。     

量子化学课程中物理量量子化的定义及应用

基于时间、空间、动量、能量存在最小基元的假设,证明了定义域区间内任意态函数均可写成正交归一动量本征态叠加的结论。不同于Dirac位置本征态的定义,基于量子化假设重新定义了位置本征态,讨论了位置本征态和位置叠加态的归一性。基于动量和坐标的定义域依据傅立叶变换给出了动量空间和坐标空间的正交基函数系。据此得出,在某些方面,重新定义的位置本征态优于传统位置本征态。     

风绕塔体流动的数值模拟

利用有限体积法对Re =2 0和Re =13 6时流体绕塔体的流动状况进行数值模拟。结果表明采用三阶精度的QUICK离散动量方程 ,并用瞬态PISO算法求解压力 -速度耦合的方法可以很好地模拟塔体背风侧的旋涡生成及脱落过程。计算结果和理论分析及经典实验结果比较一致 ,由此可以更好地理解卡曼涡街的结构     

塑料熔体在注塑模中的三维流动模拟

建立了非等温条件下黏性、不可压缩、非牛顿流体流动的控制方程.为了避免同时求解耦合的压力场、速度场,通过修改传统方法的变分方程导出了关于压力场的拟Poisson方程,用迭代法独立求解连续性方程、动量方程,并进行速度场-黏度迭代求出最终的压力场、温度场.这种方法可以减少内存,提高数值方法的稳定性,避免了Hele-Shaw模型中容易引起争议的“中面”概念,并能模拟中面方法不能模拟的一些物理现象.算例表明数值结果与实验结果吻合较好,这种方法可以成功地预测注射成型流动过程中的重要特征.     

注塑充模过程平均模腔压力的研究

本文采用有限元法、根据连续性、动量和能量守恒方程,建立数学模型,模拟了LDPE 在注塑过程中的平均模腔压力和充模时间。模拟结果已由实验值得到证实。从而为研究在不同工艺参数条件下模具型腔内的压力变化规律提供了理论依据。     

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。     

径向流动反应器流体力学特性研究进展

论述了流体在多孔流道中的变质量流动特性，建立了基于机械能全能量守恒方程和动量交换方程的径向反应器流体力学模型，分析了动量交换系数对流道静压分布计算的影响。结果表明，模型计算在小型或模拟设备中得到了证实，但在大型工业设备中是否适用尚待检验；建模理论分析中忽略了位能或重力的影响，均假设流体纯径向穿过催化床，此假设所隐含的模型适用条件尚待阐明。     

Simulation of reacting flow during filling in reaction injection molding (RIM)

This paper deals with computer simulation of the filling stage of the Reaction Injection Molding (RIM) process for cavities of rectangular, cylindrical, and disc shapes. The computer model is in two parts: the main flow and the flow by the moving front. In the main flow part, the transient equations of axial momentum, energy and species conservation and also the continuity equation are solved numerically by finite-difference methods using a moving, changing mesh. In the flow front part, which is quite novel, the transient (parabolic) vorticity, energy and species conservation equations and the elliptic streamfunction equation are again solved by finite-difference methods. An important feature of both parts is that convection along and across the flow is included in all the transient equations. Results are presented for all three cavity shapes and those for rectangular cavities are compared with the experimental results of previous investigators.     

水平管路油气混输模拟技术

以双流体模型为基础,建立了适用于水平油气混输管路的瞬态数学模型,并讨论了模型的求解以及分层流的结构方程对计算结果的影响。在大型多相流实验环道上进行了大量的混输瞬变流动过程实验,利用实验和现场数据对瞬态模型模拟得到的混输管道中的平均持液率、压降以及瞬变过程的入口压力、持液率等流动参数等进行了验证和计算,结果表明建立的模型可以比较准确地预测油气混输管路中的流动参数。     

Comparison of isothermal and non-isothermal pipeline gas flow models

The transient flow of gas in pipes can be adequately described by a one-dimensional approach. Basic equations describing the transient flow of gas in pipes are derived from an equation of motion (or momentum), an equation of continuity, equation of energy and state equation.In much of the literature, either an isothermal or an adiabatic approach is adopted. For the case of slow transients caused by fluctuations in demand, it is assumed that the gas in the pipe has sufficient time to reach thermal equilibrium with its constant-temperature surroundings. Similarly, when rapid transients were under consideration, it was assumed that the pressure changes occurred instantaneously, allowing no time for heat transfer to take place between the gas in the pipe and the surroundings.For many dynamic gas applications, this assumption of a process having a constant temperature or is adiabatic is not valid. In this case, the temperature of the gas is a function of distance and is calculated using a mathematical model, which includes the energy equation.In the paper, a comparison of different (isothermal and non-isothermal) models is presented. Practical examples have been used to emphasize differences between models.     

水平气液混输管道清管操作实验与数值模拟技术

A pigging model incorporating three different regions was developed for predicting the dynamics of the pigging operation in two-phase flow pipelines. The model incorporates a transient two-fluid model. The mixed Eulerean-Lagrangian approach was used to couple the transient model and the pigging model which can predict the pigging time, velocity and the change of pigging parameters. An experimental study was carried out to acquire two-phase transient flow and pigging data on a 380 m long, 81 mm diameter horizontal pipeline. A computer-based data acquisition system was used to obtain detailed information of the flow behavior during experimental runs. The data include pigging time, inlet pressure, accumulated liquid in pipeline, pressure and pigging velocity distribution. The predicted results compared fairy well with the experimental data.     

Three‐dimensional simulation of multi‐material injection molding: Application to gas‐assisted and co‐injection molding

This paper presents an overview of the results obtained at the Industrial Materials Institute (IMI) on the numerical simulation of the gas‐assisted injection molding and co‐injection molding. For this work, the IMI's three‐dimensional (3D) finite element flow analysis code was used. Non‐Newtonian, non‐isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved to track polymer/air and skin/core materials interfaces. Solutions are shown for different thin parts and then for thick three‐dimensional geometries. Different operating conditions are considered and the influence of various processing parameters is analyzed.     

输气管道中气油水和水合物的瞬态流动特性数值研究

对输气管道中气油水以及水合物的流动特性进行了四相四组分的数值计算研究。应用了相行为模型以及水合物相平衡模型对多组分的混合流动热力性质和水力特性进行研究。提出了相关的控制方程,并对流体与管壁之间的质量、动量以及热传递物理现象进行了描述。应用交错网格技术和有限差分法对控制方程进行求解,对边界条件和相的消失以及出现做出了很好地描述。用前人的调查结果对本文的模型进行了验证。应用此模型对管道中的流体流动特性进行了数值模拟,并通过分析所得结果对水合物的形成位置或潜在的形成位置进行了预测;通过对油气水以及水合物的水力流动特性进行分析,给出了输气过程中防止水合物的形成的方案。     

Integration of ECT measurements with hydrodynamic modelling of conventional gas-solid bubbling bed

The electrical capacitance tomography (ECT) provides fast images of the cross-sectional concentration distribution of solid-gas flow in a confined volume. This information can be integrated with numerical simulation to estimate some of the most important hydrodynamic quantities in solid-gas flow, such as the particles velocity, interstitial gas velocity and particle-particle contact forces.In this study, using the two-fluid approach, momentum and energy balance equations, along with the appropriate boundary conditions, have been solved by integrating the numerical procedure with the experimental data of the fluidised bed pressure drop and pixel distribution of particle concentration available from the ECT measurements. Preliminary results of time-dependent hydrodynamic features of the bed are presented. These results were analysed and assessed using the available experimental literature data on conventional bubbling fluidised bed. In general, it is demonstrated that the integration of ECT measurements with numerical modelling offers a unique and promising technique for comprehensive non-intrusive information on gas-solid flow systems.     

Effects of surface-active agents on mass transfer of a solute into single buoyancy driven drops in solvent extraction systems

Numerical simulation was made of transient mass transfer to a surfactant contaminated buoyancy-driven drop controlled by appreciable resistance in both liquid phases. For this purpose, the momentum equations were formulated and solved in a boundary-fitted orthogonal coordinate system. On the basis of resolved hydrodynamics of the contaminated drop, the transient mass transfer was formulated and solved in the same coordinate system. In order to check the applicability of the numerical scheme, single drop extraction experiments were conducted in a totally closed droplet file column with the terminal effect efficiently eliminated. The MIBK-acetic acid-water system was used with small quantities of SDS (sodium dodecyl sulphate), Triton X-100, or Tween 80 introduced into the continuous phase. For these experimental cases, the flow field and the drag coefficient of a contaminated drop were simulated first. The numerical prediction of the drag coefficient is found in good agreement with the corresponding experimental data. It illustrates that the behavior of a drop approaches that of a rigid sphere and that about 100 times higher bulk concentration of SDS than that of Triton X-100 is required for the same extent contamination of a MIBK drop of the same size. Then the information of the flow field of a contaminated MIBK drop was used in simulating the transient mass transfer of solute into the drop. The resulted extraction fraction and overall mass transfer coefficient are in reasonable coincidence with the experimental data. Both numerical results and experimental data show that overall mass transfer coefficient of a heavily contaminated drop is only about one third of that in the pure system. This can be explained well by the distribution of the local Sherwood number, which drops down abruptly along the rear stagnant surface. Also the interfacial resistance of adsorbed surfactant was incorporated in the mass transfer model and then estimated by the least square fitting the simulation with data. The numerical results also show that Tween 80 presents obvious interfacial resistance on the acetic acid diffusing across the interface, whereas SDS and Triton X-100 show no interfacial resistance. It is suggested that the numerical simulation can be resorted in some solvent extraction systems containing surfactants to conduct numerical experiments and parametric study.     

Rotary cylinders: Transverse bed motion prediction by rheological analysis

A method for predicting the transverse motion of a granular bed in a rotary cylinder is proposed, based on a non-Newtonian rheological model of the pseudo-plastic type, i.e. with a flow behaviour index (n) between 0 and 1. For a good simulation of bed motion, the model must be able to adequately reproduce the bed velocity profile in both the upper (downward flowing) and the lower (upward moving) zones. It is shown that to do so there is the need to adjust not only the consistency index K but even more importantly the flow behaviour index, n. The mass and momentum conservation equations are solved by the CFD code FLUENT. The model is applied to the simulation of the motion of an alumina bed and the computed results compared with experimental data.     

搅拌槽内三维流场的数值模拟

应用商业计算流体力学软件CFX对搅拌槽内的流场进行了模拟,并与PIV测试结果进行了比较,流型吻合良好.速度分量的对比结果表明不同情况与各种模型的吻合情况不尽相同,标准k-ε双方程模型、RNG k-ε模型和代数应力模型在主流域内都能较准确地模拟搅拌槽内的流动场.