微尺度型腔内液态金属流动规律模拟研究

修正了传统的Navier-Stoke方程,并利用修正后的方程与Fluent软件对微尺度型腔内Zn-Al合金微流动规律进行了数值模拟.模拟结果表明：液态金属在微尺度管道内的流动规律在管径为0.5mm时出现临界状态,管径越细,速度附面层相对厚度就越大.同时,微管流动存在着宏观流动中没有的“凸进效应”,且随着入口压力增大,流动前沿自由液面的凸进效应减弱.在流动前沿区域和上游区域之间出现负压力梯度区,且管径越细越明显. 关键词： 微管道 微流动 Zn-Al合金     

丁胞型强化换热管的数值模拟

在换热器管道的内壁面上布置丁胞可以有效地增强管道内的传热.通过三维数值模拟,对含丁胞的圆形截面管道内的定常不可压缩湍流流动进行了数值模拟.本文采用RNG k-ε方程模型作为湍流计算模型和SIMPLE算法求解管道的流动传热情况.数值模拟结果表明,丁胞的大小、深度、排列密度等几何结构均对管道的换热效果有一定影响.在较低雷诺数下,含较小丁胞的管道换热效果好于含较大丁胞的管道;在较高雷诺数下,含较大丁胞的管道换热效果好干含较小丁胞的管道.     

直接模拟蒙特卡罗方法在微通道流动模拟中的应用

直接模拟蒙特卡罗方法是一种求解稀薄气体流动换热新的数值方法。本文采用该方法对Kn数跨越速度滑移区和过渡区的三个微通道内的流动进行了数值模拟,给出了通道内速度、压力及局部阻力系数的变化曲线.为了表明通道横纵比对流动的影响,还对每个算例在不同的横纵比下进行了比较。结果表明,微通道内的流动特性不仅与Kn数有关,而且与通道的横纵比也有很大的关系。     

气体混合流动的DSMC方法模拟

气体混合流动在MEMS的应用中常常遇到.本文采用直接模拟Monte Carlo方法研究了氮气和氧气在微尺度中的流动混合问题.数值模拟中设定两种气体分别以不同的速度,相同的数密度进入微槽道.当经过分割平板之后,两种气体发生混合.在对结果的分析中发现,进入速度对两种气体完全混合后的混合距离,以及完全混合后的单组份气体占混合气体的比例都会产生重要的影响.     

聚变堆液态包层准二维磁流体湍流模型研究

为研究聚变堆氚增殖包层中液态金属湍流磁流体动力学(MHD)效应,开发了一种新的准二维单方程 MHD 湍流模型,并进行了相关数值模拟程序的编制及验证。对于矩形管道中的准二维 MHD 湍流流动,三维流 动主要发生在哈德曼层中,中心的主流区呈现出二维流动。为了反映这种特殊的流动特征,新湍流模型在标准 k-ε 模型的基础之上去掉了传统的耗散项,代之以电磁耗散项来模拟湍流 MHD 效应。同时,采用 Bradshaw 假设来对 湍流涡粘系数进行模化。为验证该湍流模型是否合理,编制了相关数值模拟程序,并利用直接数值模拟(DNS)结 果对该程序进行了校正,数值模拟结果与 DNS 结果吻合较好。计算结果表明,该湍流模型可应用于聚变堆液态 包层 MHD 湍流流动的数值模拟。     

电机转子内部通风冷却系统的流动分析与结构改进

本文根据某电机通风冷却系统的总体流动性能分析结果,采用数值模拟方法分析了该电机转子冷却系统中形状最为复杂、流动损失最大的旋转槽道内部三维流场.采用区域分块与边界拼接方法建立网格系统,数值计算结果表明,该旋转槽道内结构存在改进空间.为减少流动的局部阻力损失,对原模型流道结构进行改进,并建立了新的三维模型.新模型数值模拟结果表明,改进后的结构可以在保证换热效果基本保持不变的情况下,大大降低槽道内部流动损失.     

Y型微通道气液两相流的数值模拟

针对Y型微通道气液两相流的数值模拟,建立了适用于微通道气液两相流的计算模型,采用CFD方法对微通道内流体的流动进行了数值研究,分析了微通道内流动状态、气泡形状以及生成周期,模拟了Y型微通道气液两相流弹状流的形成过程,并对弹状流的压力、速度、壁面剪切应力的分布、变化趋势及原因进行了深刻剖析,揭示了弹状流流动规律,为进一步加强弹状流应用打下基础,为微通道中的气液两相流动提供了可靠的理论依据。     

变截面微管道内声速点位置及临界压比

等直-收缩-扩张-等直（SCDS）变截面微管道主要应用于微型空间推进器和微型气体涡轮机等微器件中，研究其内流动特性对指导上述两种微器件的设计和性能的提高具有非常重要的意义.采用硅微加工技术在硅片上制作出矩形截面三维SCDS微管道，喉部宽度为16μm，深度为20μm，收缩比为1.625∶1实验测量了不同进出口压比条件下微管道内氮气的流量特性.实验设定进出口压比值范围为1.0—4.0，由此出口体积流量范围为0—0.12mL/s，流动的特征雷诺数小于350在实验研究的基础上，采用有限体积法对其内部流动特性进行了数值模拟，数值模拟结果与实验结果相符合.数值模拟结果发现两点不同于常规流动的特异现象：其一为最早出现声速点不在最小截面喉部附近，而是移到出口截面附近，即声速点的位置发生变化；其二为在进出口压比达到4.0时，SCDS微管道内部流场才出现声速点，即临界压比值（这里将管道内部首次出现声速点时对应的当地点压力与进口压力的比值定义为临界压比）发生变化.将其原因归结为表面效应（表面积与体积比值S/V）的影响，并进一步研究了这两点特异现象与S/V值之间的关系. 关键词： 等直-收缩-扩张-等直变截面微管道 声速点位置 临界压比 表面积与体积比值     

光滑矩形微通道液体单相流动和传热的数值研究

采用CFD方法对水在矩形光滑微通道内的流动和传热特性进行了数值模拟.计算结果表明微通道的长径比、当量直径、高宽比和孔隙率都对其流动和传热有着不同程度的影响.在保持长径比大于70而使流动的入口效应可忽略的前提下,分别模拟了当量直径,高宽比和孔隙率对微通道流动和传热的影响,得到了各种工况下的流动和传热规律.     

过渡区微尺度流动的有效黏性多松弛系数格子Boltzmann模拟

为提高采用二维九速离散速度模型的格子Boltzmann方法 (LBM)模拟微尺度流动中非线性现象的精度和效率,引入Dongari等提出的有效平均分子自由程对黏性进行修正(Dongari N,Zhang Y H,Reese J M2011 J.Fluids Eng.133 071101);并针对以往研究微尺度流动时采用边界处理格式含有离散误差的问题,采用多松弛系数格子Boltzmann方法结合二阶滑移边界条件,对微尺度Couette流动和周期性Poiseuille流动进行模拟,并将速度分布以及质量流量等模拟结果与直接模拟蒙特卡罗方法模拟数据、线性Boltzmann方程的数值解以及现有的LBM模型模拟结果进行对比.结果表明,相对于现有的LBM模型,引入新的修正函数所建立的有效黏性多松弛系数LBM模型有效提高了LBM模拟过渡区的微尺度流动中的非线性现象的能力.     

Simulation of shock-wave propagation in the argon plasma of a positive column discharge

The computer simulation of shock-wave propagation in the argon plasma of positive column discharge was performed. A one-dimensional model of the gas-discharge plasma is used, which comprises the continuity equations for the electron and ion plasma components and the equation of electrostatics with allowance for initial and boundary conditions. The distribution of plasma parameters in the shock wave was obtained; the effect of its intensity was evaluated. The simulation results were compared with experimental data.     

Simulation of elastic wave propagation in cylindrical structures including excitation by piezoelectric transducers

The development and optimization of non-destructive testing procedures usually needs experimental data. As experiments are time-consuming and expensive to conduct, we would like to use numerical data instead. This is admissible, if the simulation describes the physical experiments accurately. A three-dimensional displacement-stress finite-difference model is presented for a piezoelectric transducer coupled to an anisotropic tube. The allocation of the displacement and stress components on a staggered grid leads to a stable scheme. A full piezoelectric model of the transducer is used, including transverse isotropy in the elastic, dielectric, and piezoelectric constants. Similar to an experiment, elastic waves are excited in the corresponding simulation by applying a voltage signal to the electrodes of the piezoelectric transducer. Predictions of the simulation model for a piezoelectric ring transducer coupled to a carbon-fibre-reinforced shell are compared to experimental results to test the validity of the numerical data.     

���������ֵģ����EAST��һ���е�Ӧ��

介绍了过冷沸腾换热的数值模拟方法以及在EAST第一壁组件冷却系统中的应用.采用双流体模型,系统分析了过冷沸腾壁面换热过程中存在的各种换热模式,给出了Fluent软件封闭关系式中所需的质量、动量以及能量的交换项的形式.采用用户自定义函数(UDF)模拟壁面沸腾气化过程,对提出的模拟方法与已发表的实验数据对比进行了校核,得出合理的结论.最后分析了过冷沸腾两相流在EAST第一壁中的工程应用,模拟了热沉冷却结构的沸腾换热现象.为EAST PFCs的冷却结构优化提供了依据.     

Three-dimensional numerical simulation of the operation of a rotating-detonation chamber with separate supply of fuel and oxidizer

A three-dimensional numerical simulation of the operation of an annular rotating-detonation chamber (RDC) with separate supply of combustible mixture components, hydrogen and air, is performed, and the calculation results are compared to available experimental data. The model is based on a system of time-dependent Reynolds-averaged Navier-Stokes equations complemented with a turbulence model and continuity and energy equations for a multicomponent reacting gas mixture. The system is solved using a coupled algorithm based on the finite volume method and particle method. Calculations are for the first time performed with allowance for effects of finite rates of turbulent and molecular mixing of the combustible mixture components with each other and with reaction and detonation products. The calculation results compare favorably with the experimental data obtained at the Lavrentyev Institute of Hydrodynamics of the Siberian Branch of the Russian Academy of Sciences.     

Simulation of thermally induced processes of diffusion and phase formation in layered Fe-Sn and Fe-Zr systems

The simulation results of thermally induced processes of diffusion and phase formation for the Fe-Sn and Fe-Zr layered systems experimentally investigated by M?ssbauer spectroscopy are presented. Simulation has been carried out using the specially designed DIFFUSION program, the basic functional possibilities of which are described in detail. The physical model is based on the phenomenological Darken theory and on the interdiffusion mechanism of components along the continuous diffusion channels of phases in two-phase regions of the system. The simulation results agree well with the experimental data. The character of phase transformations in the investigated layered systems is determined by the change in a local concentration of components during their interdiffusion and corresponds to the features of the equilibrium diagrams for both binary systems.     

Estimation of the thermodynamic parameters of a shock-wave action on high-porosity heterogeneous materials

The properties of high-porosity powder mixtures during shock-wave loading are determined using a thermodynamically equilibrium model. The calculations performed with this model agree well with the data obtained from experiments over a wide pressure range. An equation of state of the Mie–Grüneisen type is used for condensed phases on the assumption of a temperature-dependent Grüneisen coefficient. The thermodynamic properties of mixtures are described for two or more condensed components over wide pressure and porosity ranges up to aerogels. Only the parameters of components are used to calculate the behavior their mixtures. The calculation results are compared with both the experimental data and the simulation results obtained by other authors.     

Computer simulation of expansion of a carbon laser plasma after ablation in nitrogen atmosphere

Computer simulation is employed for analyzing the dynamics of plasma expansion in nitrogen under a pressure of 103 and 104 Pa after the action of a nanosecond laser pulse on a graphite plate for obtaining carbonitride nanofilms with the help of laser ablation technology. The binary gas mixture is described using a macroscopic quasi-gasdynamic model taking into account momentum and energy transfer between mixture components. The results of simulation are compared for various initial values of temperature and pressure of the laser jet with the results of direct Monte Carlo simulation and with experimental data. The possibility of controlling the shock wave propagation modes after ablation by varying the initial values of gasdynamic parameters is demonstrated. The effect of nitrogen atmosphere on the propagation of the laser jet is studied.     

Coupled dynamics of a squeeze-film levitated mass and a vibrating piezoelectric disc: numerical analysis and experimental study

This work deals with the dynamics of a vibrating piezoelectric disc, which creates, under specific vibrating conditions, an air squeeze film that is able to levitate a freely suspended object.In such problems, the coupling effects between the various components affect the overall dynamical behaviour of the combined system. For complex systems, which combine elastic and electro-static effects together with compressible fluid effects, the coupled equations are often dealt with separately to avoid modelling and computational complexity. In this paper, the importance of handling such systems in a coupled manner is advocated by means of numerical and experimental examples. A coupled model is derived in this work making use of a concise numerical solver to allow for this investigation under several conditions. The piezoelectric part of the structure is modelled by finite elements while the squeeze film phenomenon is represented by means of finite-difference equations, to model a variant of the Reynolds equation. The numerical model was verified during each step in the development of the numerical algorithm and indeed showed good agreement with existing publications, but once the components were combined, it was found that several phenomena were misrepresented in the past due to the neglect of the coupling effects. Several physical insights are brought from the simulation and investigation of the numerical results. In the last part, the importance of coupled analysis is emphasized by introducing an experimental investigation of the dynamical behaviour while conducting a comparison with numerical simulation results. From this comparison, the limitations of state-of-the-art modelling procedures are clarified.     

Time-domain simulation of sound production of the sho

A physical model based on the sound production mechanism of the sho is proposed with intention of applying it to sound synthesis. Time-domain simulation was done using this model, and effects of the tube length and blowing pressure on the sounding frequency and sounds spectra were investigated. The reed vibration, pressure variation inside the tube, and threshold blowing pressure for oscillation were measured by artificially blowing air into the sho. The experimental results are in acceptable agreement with simulation results in terms of the relationships between tube length and threshold pressure and between tube length and the sounding frequency. In addition, recorded sound waveforms and simulated ones have a common feature in the sense that high-frequency components of their spectra increase with increasing blowing pressure. Further, it is concluded that a sho reed acts as an "outward-striking valve."     

Finite-rate chemistry effects in turbulent opposed flows: comparison of Raman/Rayleigh measurements and Monte Carlo PDF simulations

This study reports results from experimental and numerical investigations of a partially premixed turbulent opposed methane/air jet flame. Experimentally determined properties of the scalar and the flow field are compared to the results from a Monte Carlo simulation. One-dimensional spatially resolved Raman/Rayleigh scattering serves to quantify the mean species concentrations and temperature, whereas laser Doppler velocimetry is used to measure axial and radial velocity components. The simulation is simplified by using a one-dimensional formulation. It includes a Reynolds-stress turbulence model and a Monte Carlo simulation of the joint scalar probability density function (PDF). A non-uniform Monte Carlo particle distribution is used to minimize stochastic errors. The flame is operated close to extinction with strong interactions between turbulence and chemistry. Comparisons between experimental and numerical results reveal a good agreement of mixture fraction profiles along the centreline. However, species scatter plots and mixture fraction PDFs show discrepancies between experiment and simulation. Numerical simulations over-predict the extinction limits and therefore under-predict the intermittent nature of turbulence and mixing of the scalars.