烟草专用标准恒流孔的研究

为了更好地测量卷烟吸阻和滤棒压降,基于计算流体动力学的角度对烟草专用恒流孔进行了研究,采用有限体积法和Realizable k-ε的湍流模型进行三维数值仿真,能够模拟烟草专用恒流孔的内部流动情况,并进行了理论、数值仿真和实验研究。实验数据和在浙江中烟标准化实验室测得的标准恒流孔入口端的体积流量的实验数据对比,综合分析后发现标准恒流孔能在其前端保持恒定的体积流量。     

平面流铸快速凝固过程的数值模拟研究进展

本文对平面流铸工艺快速凝固过程的数值模拟研究现状作了介绍。主要内容包括 :(1)对溶潭的形成及特征、平面流铸工艺参数对条带形成及质量的影响的数值模拟 (2 )结合快速凝固过程的形核和晶体生长的动力学特征对平面流铸凝固过程的数值模拟 (3)平面流铸过程界面传热系数的数值模拟。文章最后 ,提出了平面流铸工艺快速凝固数值模拟研究的进一步发展方向     

Impact of Artificial Compressibility on the Numerical Solution of Incompressible Nanofluid Flow

The numerical solution of compressible flows has become more prevalent than that of incompressible flows. With the help of the artificial compressibility approach, incompressible flows can be solved numerically using the same methods as compressible ones. The artificial compressibility scheme is thus widely used to numerically solve incompressible Navier-Stokes equations. Any numerical method highly depends on its accuracy and speed of convergence. Although the artificial compressibility approach is utilized in several numerical simulations, the effect of the compressibility factor on the accuracy of results and convergence speed has not been investigated for nanofluid flows in previous studies. Therefore, this paper assesses the effect of this factor on the convergence speed and accuracy of results for various types of thermo-flow. To improve the stability and convergence speed of time discretizations, the fifth-order Runge-Kutta method is applied. A computer program has been written in FORTRAN to solve the discretized equations in different Reynolds and Grashof numbers for various grids. The results demonstrate that the artificial compressibility factor has a noticeable effect on the accuracy and convergence rate of the simulation. The optimum artificial compressibility is found to be between 1 and 5. These findings can be utilized to enhance the performance of commercial numerical simulation tools, including ANSYS and COMSOL.     

微圆管内R1234ze(E)流动沸腾的环状流特性模拟研究

本文建立了制冷剂R1234ze(E)在微圆管内流动沸腾过程中的环状流模型,对传热和气液两相流动压降进行了模拟研究。综合考虑重力、表面张力及气液界面剪切力的影响,模拟分析了周向液膜不均匀分布特性及该特性对流动与换热的影响,经验证,计算结果与已有实验结果吻合较好。本文还研究了不同因素对环状流区域表面传热系数与压降的影响。模拟结果表明:在流动起始区域,截面液膜厚度的分布受重力作用影响,随着流动沸腾过程的进行,该影响作用开始减弱,且有重力作用时的环状流平均表面传热系数高于无重力作用时的环状流平均表面传热系数,随着重力加速度的增加,环状流的平均表面传热系数不断增大;随着质量流速的增大,表面传热系数与压降均随之增大;随着管径增大,表面传热系数与压降均随之减小。     

基于矩形流道流场分析及气动实验的轴流风机结构参数优化设计

本文通过提取导流罩的轴向长度及叶顶间隙两个设计参数,构建了矩形流道内轴流风机的流场结构及仿真模型,进行了数值模拟和实验分析。结合仿真模型分析了矩形风道下轴流风机内部和出口流场特性的变化规律,构建了风机设计参数与气动性能之间的映射关系模型。通过风机气动性能实验可得:风机出口静压、体积流量和效率与间隙因子成反比,而与长度因子成正比,对比模拟值和实验值验证了模型的正确性。基于量化映射关系模型得到风机设计参数间隙因子和长度因子的最优值分别为0.8%和12.5%,为风机设计和冰箱风道优化提供量化参考。     

Computation of Stokes Flow due to the Motion or Presence of a Particle in a Tube

The computation of Stokes flow due to the motion or presence of a rigid particle in a fluid-filled tube with arbitrary geometry is discussed with emphasis on the induced upstream to downstream pressure change. It is proposed that expressing the pressure change as an integral over the particle surface involving (a) the a priori unknown traction, and (b) the velocity of the pure-fluid pressure-driven flow, simplifies the numerical implementation and ameliorates the effect of domain truncation. Numerical computations are performed based on the integral formulation in conjunction with a boundary-element method for a particle translating and rotating inside a cylindrical tube with a circular cross-section. The numerical results are consistent with previous asymptotic solutions for small particles, and complement available numerical solutions for particular types of motion     

搅拌摩擦点焊金属流动研究现状

搅拌摩擦焊是一种高效环保的固相连接技术。搅拌摩擦点焊是在传统的搅拌摩擦焊上发展起来的一种新型点连接技术,与传统的电阻点焊等连接方法相比具有诸多优势。目前国内外搅拌摩擦点焊工艺在航空及汽车等工业领域有广泛的应用,但是其成形机理并不清楚。基于已发表的文献,详细综述了在搅拌摩擦点焊过程中,材料的流动模型以及数值模拟等方面的研究进展。     

基于PIV技术的复合流道板式结构实验

目的在包装工程流场测量的研究中,验证粒子图像测速(PIV)技术的可行性。方法用超白玻璃制作复合流道板式换热器的模型,基于PIV技术采集被测区域图像,应用互相关分析法进行计算,获得流场数据,并与数值模拟结果比对进行验证。结果实验结果流型清晰,数据和数值模拟基本一致。结论PIV技术可应用于流动复杂、非接触的包装工程类的流场测量,且超白玻璃是一种理想实验材料,能够为拓展该领域的探索思路提供参考。     

Numerical Analysis of the Effect of Diffusion and Creep Flow on Cavity Growth

In this paper, intergranular cavity growth in regimes, where both surface diffusion and deformation enhanced grain boundary diffusion are important, is studied. In order to continuously simulate the cavity shape evolution and cavity growth rate, a fully-coupled numerical method is proposed. Based on the fully-coupled numerical method, a gradual cavity shape change is predicted and this leads to the adverse effect on the cavity growth rate. As the portion of the cavity volume growth due to jacking and viscoplastic deformation in the total cavity volume growth increases, spherical cavity evolves to V-shaped cavity. The obtained numerical results are physically more realistic compared to results in the previous works. The present numerical results suggest that the cavity shape evolution and cavity growth rate based on the assumed cavity shape, spherical or crack-like, simply cannot be used in this regime.     

Flow efficiency of perforated systems – a combined analytical and numerical treatment

The effect of the spatial distribution of perforations on the flow from the reservoir to the wellbore for single phase liquid flow is studied. The reservoir is taken to be isotropic and, for most of the paper, the model used here assumes that the perforations and the wellbore are both undamaged. Thus, there is no change of permeability around the wellbore and perforations. The pressure/flow along a single perforation is studied in detail first and an integral equation is derived which can be solved numerically to give the pressure/flow everywhere along the perforation. The interaction of the perforations is considered by an approximation in which each perforation is represented by a point source of unknown strength positioned at the centre of the perforation. A simple ellipsoidal model of the perforation is also considered which provides a faster approach for evaluating the flow. The resulting flux of fluid from each perforation into the wellbore is presented numerically for the above-mentioned approximate methods and the comparison with the full numerical method is also made. For the ellipsoidal perforation, the modelling of the perforation skin effect (a mathematical treatment of pressure drops which is caused by perforation damage) is also described, but no detailed numerical results are given.     

纺锤体流量计的流场数值模拟

介绍了一种新型的节流式差压流量计——纺锤体流量计（又名槽道流量计）。数值模拟结果表明,在来流规则或畸变情况下纺锤体等直径段部分均能很好地形成环形槽道流动,使测量重复性和精确度得到大幅提高成为可能;同时,由于完全避免了流动分离,在高雷诺数下的压力损失与所得差压之比可小于孔板流量计的二分之一。实验结果验证了数值模拟的可靠性。     

基于康达效应的热缩烘箱流场分析及结构优化

目的对壁纸包装机烘箱进行建模与分析,优化烘箱结构。方法基于流体力学,建立热收缩烘箱的能量方程和运动学方程。通过数值计算得到烘箱流场分布及仿真云图,进而研究烘箱喷口、底面、回风口的流场分布及对热缩性能的影响。基于计算结果,进行回风口尺寸和结构的改进与优化,对多种拟定的改进结构进行分析计算,提取计算数据并对比确定相对最优模型。结果将确定的最优改进模型加入烘箱中进行整体模拟计算,提取优化后的计算数据,完成结构优化设计。结论优化后的壁纸包装机烘箱结构在一定程度上改进了原结构中存在的不足,能够较好地满足壁纸包装工程中的工艺需要。     

Flow separation control in open-channel bends

The investigation of fluid flow in sharp open-channel bends is key to controlling undesired sedimentation in natural river reaches. The difficulties are associated with controlling the flow separation in meanderings. Flow separation decreases the width of the flow, and consequently, the conveyance capacity while increasing erosion and mixing. This study proposes a novel approach to reduce the flow separation at the inner banks of sharp open-channel bends. Three-dimensional numerical experiments were conducted. To find the most reliable procedure, five turbulence models were examined. The employed numerical approach is formulated within the framework of the finite volume method and the volume of fluid (VOF) technique to solve the Navier–Stokes equations. Water levels and velocity profiles are obtained in different sections of the channel and are compared to experimental studies of a 90° sharp open-channel bend. A close agreement is observed using the RSM (Reynolds stress model) turbulence model. Moreover, the evaluation of acquired velocity profiles demonstrates that in a regular bend, the lowest velocity occurs near the inner bank, where it has a flow separation tendency. The same numerical procedure is employed to simulate water flow through a sharp converging open-channel bend. The measurements of velocity profiles and velocity vectors in the curved sections support the idea that decreasing the channel width considerably reduces the overall velocity variations in cross-sectional areas of the test case and is effective to control flow separation.     

微注塑成型流动中熔体壁面滑移的研究

基于宏观熔体流动的基本理论及其流动过程中壁面滑移机理的分析,针对微注塑成型模具中熔体充模流动时的壁面滑移行为,建立了微小通道中高聚物熔体流动的壁面滑移理论模型。并用数值模拟方法,对不同滑移系数时微小通道中熔体的壁面滑移对流动速度、熔体压力等的影响进行了研究。结果表明,微小通道中的壁面滑移可使壁面处熔体的流动速度增加,压力损失减小,有利于熔体的充模流动。     

颗粒流的离散元法模拟及其进展

颗粒流问题是众多工农业生产领域中的常见问题,然而人们至今对颗粒流机理认识不深。目前一种基于离散元的数值模拟方法被用以模拟和分析颗粒流问题,研究实践表明该方法是散体力学分析的一种有效的工具。本文介绍了颗粒流研究的背景以及离散元法的发展过程,概述了颗粒流动力学研究的动理论模型和摩擦塑性模型,综述了离散元法的理论和各种颗粒作用模型及其在粉体工程领域的应用,讨论了颗粒流研究的主要困难和离散元法发展中亟待解决的问题。     

验证流动分析中数值解的新思路

为了解决流体流动分析中存在的实验条件和实验手段缺乏物问题,本指出了利用计算的流动空间和实际流动空间相对比来验证计算结果的方法;并阐述了如何获得计算的流动空间以及如何运用这种验证方法。     

抽水量对地下水源热泵抽灌井设计间距的影响

通过建立地下含水层水-热耦合数学模型,用数值模拟的方法分析了热负荷变化以及热负荷不变两种情况下抽水量对抽灌井设计间距的影响问题,为寻求合适的抽灌井设计间距提供参考依据.     

簧片阀流量系数的实验研究与数值模拟

在压缩机簧片阀的数值模拟中,簧片阀的流量系数和相应的有效流通面积是须预先知道的关键参数。一般来说,流量系数和有效流通面积是通过实验测得的。但是,当制冷剂在封闭的系统中流动时,很难测得簧片阀的流量系数。本论文提出了一种思路,建立以空气为工质来测量簧片阀流量系数的模型,同时用静态吹风实验来测量空气的流量系数,得到了空气在不同流量和阀片升程下的流量系数。改变工质为R600a后,模拟计算了簧片阀的流量系数,并通过压缩机整机性能实验对流量系数的正确性进行了间接的验证。结果表明:以空气为工质模拟计算的流量系数与实验结果符合较好,这一模型能够用于计算工质为R600a时的流量系数。     

Symmetry-Preserving Discretization of Heat Transfer in a Complex Turbulent Flow

Convective and diffusive operators are discretized such that their symmetries are preserved. The resulting discretization inherits all symmetry-related properties of the continuous formulation. It is shown that a symmetry-preserving discretization is unconditionally stable and conservative. A fourth-order, symmetry-preserving discretization method is developed and tested for the numerical simulation of turbulent (flow and) heat transfer in a channel with surface-mounted cubes, where the temperature is treated as a passive scalar. The Reynolds number (based on the channel width and the mean bulk velocity) is Re=13,000. The results of the numerical simulation agree well with available experimental data.     

变截面梁-板耦合结构的功率流

介绍了用微分变换法求解变截面梁的振动,并对变截面梁-板耦合结构的功率流进行了研究,分析了梁的不同结构参数对功率流传递的影响,为梁-板耦合结构的减振设计及新型梁式宽带吸振器的设计提供了重要参考。