Numerical simulation of interaction between arc discharge and transverse magnetic field

An unsteady-state three-dimensional numerical model of radiation magnetogasdynamics is used to calculate the structure of an arc discharge which interacts with an external transverse magnetic field and transverse gas flow. The velocity field and the distribution of gas temperature obtained as a result of calculations agree with experimental data. The difference between the calculated and measured values of temperature in the discharge column is approximately 5%.     

High-temperature interaction of uranium and zirconium with water vapor

We analyze physicochemical processes of interaction between uranium, zirconium, and its alloy (with 1% Nb) with water vapor at temperatures up to 1500°K and study mechanisms and kinetics of these processes. It is shown that, up to 700°K, the kinetics of the process of oxidation of uranium is described by a linear function of time; at temperatures higher than 900°K, this dependence becomes parabolic. Our interpretation of the mechanism of the process of oxidation of uranium takes into account the influence of structural defects and electrochemical properties of uranium oxides formed in the course of this process. The process of oxidation of zirconium and its alloy with 1% Nb by water vapor obeys a cubic law in the temperature range 900–1200°K and a parabolic law in the range 1300–1500°K. The comparative analysis demonstrates that the hydrogen release rate in the process of uranium oxidation is about twice as high as in the process of vapor-zirconium reaction.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3, pp. 36–43, May–June 1995.     

Numerical simulation on interaction between TIG welding arc and weld pool

The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established in this paper. The moving interface was solved by updating the calculation region of arc and weld pool continually. Fluid flow and heat transfer of TIG welding arc and weld pool were analyzed basing on this model. The weld pool shape calculated by dynamic coupling welding arc and pool is more close to the experiment than that of non coupling calculation.     

Numerical simulation of boundary-layer disturbance evolution

The use of numerical simulations to study the development of boundary-layer disturbances is illustrated for a number of different incompressible flow configurations. These include cases where the disturbances are generated by, or interact with, flow-control devices in the form of compliant panels, suction slots and microelectromechanical systems actuators. The velocity-vorticity system of governing equations used for the simulations is reviewed, along with the numerical discretization.     

Numerical simulation of the interaction between reflected shock wave and near-wall boundary layer

The interaction of a shock wave, reflected from the flat end of a cylindrical shock tube, with a cocurrent gas flow at the side wall, is considered in the axisymmetric case. The Navier-Stokes system of equations has been numerically integrated in the thin layer approximation using a predictor-corrector scheme. The appearance of a recirculation gas flow structure behind the reflected shock front and the evolution of this structure in the reflected wave going away from the tube end are analyzed. The corresponding patterns of constant density lines and the velocity vector field are presented.     

液氢泄漏扩散数值模拟研究

通过ALOHA软件进行了不同风速、环境温度、泄漏量扩散模拟,分析了不同风速、温度、泄漏量条件下的扩散规律。结果表明,泄漏扩散距离随着风速的增大而变小,风速越大,泄漏扩散范围越小;泄漏扩散距离随着环境温度的升高而变大,温度越高,泄漏扩散范围越大;泄漏扩散距离随着泄漏量的增加而变大,泄漏量越大,泄漏扩散范围越大。将液氢蒸发和氢气扩散试验的体积分数数据与ALOHA软件模拟数据进行对比,结果表明:ALOHA软件对氢的体积分数值模拟结果具有良好的精度,在液氢泄漏事故应急中具实用性。     

Numerical simulation of the interaction forces between turbine meter and particles in a standpipe

A numerical study of the dynamic behaviour of a turbine meter measuring solid flowrate was carried out by use of the discrete element method. The simulation was conducted with a cylindrical standpipe of 30d in diameter and 40d high, filled with 30000 mono-sized spheres of diameter d, and with a turbine fixed at the centre of the standpipe at a height of 20d. The variations of the torque and rotational speed of the turbine and the porosity of particles around the turbine with time were first investigated. It was observed that these variables fluctuate significantly at the initial stage and gradually reach a macroscopically steady stage. The dependence of the resultant rotational speed on solid flowrate was then measured and shown to be qualitatively comparable to the experimental observation. The force structure of particles around the turbine and the statistical distributions of the forces and torques acting on the turbine originated from its interaction with neighbouring particles were finally analysed. The results indicate that the torque originated from the particle-blade interactions on the blade top surface acts as a driving torque to make the turbine rotate, while the torques due to the particle-blade interactions on the blade bottom and side surfaces balance this driving torque, leading to a macroscopically constant rotational speed.KeywordsDiscrete element simulation, granular dynamics, flow measurement, turbine meter     

Numerical simulation of carbide and nitride precipitate evolution in steels

A numerical method of simulation of carbide and nitride precipitates evolution in steels at isothermal annealing is described. This method is based on the mean field approximation and consideration of precipitates evolution in field cells. Not only the growth and dissolution of the particles present, but also the nucleation of the new ones is taken into account. This method enables to simulate the precipitates evolution at all the stages beginning from the nucleation and up to the stationary coarsening. The results of kinetic calculations of vanadium carbides evolution in steels for different initial particle size distributions are presented and analyzed.     

钐铁熔体高压雾化氮淬过程的数值模拟

为探究钐铁熔体气雾化过程中高压环境和雾化介质组分对雾化结果的影响规律,基于紧耦合气雾化喷嘴结构,采用Fluent软件对熔体高压气雾化淬冷过程进行模拟,分析不同环境压力和氮气-氩气混合组分下的熔体雾化氮淬过程。结果表明,环境压力越大雾化效果越好,纯氮气组分下达到相对理想的雾化效果的最低环境压力为3.0 MPa;随着氩气含量的增加,雾化效果在较低的环境压力下提前达到相对理想的稳定程度,但过多的氩气不利于雾滴的冷却与后续熔体渗氮的研究,综合考虑雾化效果较理想的条件为,氮气、氩气体积比为1:3,环境压力为2.0 MPa。     

氢低温套管式换热器模拟及实验验证

建立了考虑外管壁轴向导热与辐射漏热的套管式换热器数值模型,对搭建的预冷型液氢温区JT制冷机中套管式换热器出口温度进行模拟,结果表明:考虑外管壁的模型与实验结果更加吻合.利用该模型计算不同压比与流量情况下换热效率变化,流量由10 mg/s升高至30 mg/s,效率降低2.70％;压比由6升高至10,效率升高0.25％.     

充型过程的数值模拟及水力模拟实验验证

为了提高充型模拟的计算精度，改进和修正了传统的用于模拟自由表面的“施-受体”算法，针对体积函数提出了新的处理自由表面的“三维施-受体”算法，为了检验新方法，对同一方形验证铸件设计了两种不同浇注系统，并对其同时进行了水力模拟实验和数值模拟计算，数值模拟计算结果与水力模拟实验结果一致，研究表明：浇注系统几何形状对充型模式有重要影响；“三维施-受体”算法减少了计算误差，提高了计算精度，不仅能够准确地预测浇注系统对充型模式的影响，而且在评估和辅助浇注系统设计方面具有巨大潜力。     

泡沫金属湍流射流发泡过程数值模拟研究

应用欧拉-欧拉双流体模型,并采用分别描述气泡和液相湍流的k-ε两相湍流模型,描述制备泡沫金属过程中气体射流发泡过程的两相流动.通过对气泡和液体在流场中的受力分析,详细讨论了阻力、升力等相间作用力对气泡分布和流体流动的影响.预测结果和文献中的实验结果进行的对比表明,在给出合理的相间作用力模型时,该模型预测值和实验结果符合较好.但由于目前尚缺乏气体射流破碎模型,喷嘴附近还存在较明显差异.     

Numerical simulation of phase transitions in two-component materials upon noncongruent evaporation

The dynamics of noncongruent phase transitions in two-component materials upon evaporation in vacuum has been numerically simulated within a model based on the assumption of local thermodynamic equilibrium in the condensed phase. The results presented for nonstoichiometric uranium dioxide irradiated by a laser pulse have been obtained with allowance for the dependence of its thermodynamic and transport properties on the temperature and composition. It has been shown that, because of noncongruent evaporation changing the composition of the material in the surface region, its melting can begin in its interior even in the case of surface heating.     

Model of intensive inter-phase interaction between high temperature melt and cold volatile fluid

The fragmentation of the molten metal drop in the cold volatile liquid was studied. Two cases of water surface temperature were investigated: a—lower than its critical meaning during direct contact with melt, and b—higher than the critical one. The criterion determining existence of the fragmentation was presented for the first case. In the second case, that is being more complicated, possibility of the direct contact between the surrounding liquid and the melted metal surface and development of the instability on both surfaces were studied. It was shown that the fragmentation mechanism for the second case is strongly dependent on the characteristic time of the direct water-melt contact. The characteristic time must be sufficient enough for liquid water to interact with the melt before generation of the vapor layer between two surfaces. The process that follows the contact of water with the melted metal and a high pressure region formation was considered. The fragmentation mechanism, based on the analogy with the known problem, when a body with a flat circular nose impacts upon a flat liquid surface, was presented. Mean velocity and mean width of the generated jets from the melt surface were calculated.     

Singularities of interaction between a cathode stream and anode vapors in a vacuum arc: Numerical simulation results

Numerical simulation is performed of the process of interaction of cathode and anode ions in a highcurrent vacuum arc with evaporating anode. The presence of the friction force between ion flows, as well as of the friction work, leads to heating and acceleration of slow anode ions and deceleration of fast cathode ions. The boundaries of stable passage of current are determined, associated with the presence of the limiting value of density of anode vapors     

Numerical simulation of the macrostructure evolution of a heavy steel ingot

The macroscopic grain structure of a 234 t steel ingot was simulated by using cellular automaton and finite element method provided by ProCAST. The growing speed coefficient of Kurz–Giovanola–Trivedi model was modified to reflect the growing process of grains. Chilled fine grains, columnar grains and coarse equiaxed grains were obtained from surface to core of the ingot, which were roughly in agreement with the measured ones. The influences of the nucleation and growth parameters were investigated. It was found that the relationship between nucleation and growth determines the macrostructure profile. An index, the ratio of growing speed over the nucleated sites at certain undercooling was proposed to estimate the macrostructure tendency.     

Effects of Sr-modification and melt cleanliness on melt hydrogen absorption of 319 aluminium alloy

The effect of Sr-modification on hydrogen content of commercial 319 aluminium alloy melts has been quantified, by using HYSCAN instrument at 685°C and 735°C. In addition, the effect of melt cleanliness on the hydrogen content of the melt has been studied. It has been found that the melt cleanliness has a significant effect on the reduction of hydrogen content of the melt. The hydrogen contents of Sr-modified cleaned melts were significantly lower (30-45%) than uncleaned melts (melts containing surface oxide layers) at both temperatures. Sr-modification had no marked effect on the hydrogen content of the melt at both temperatures, when measurements were carried out in a cleaned melt. Hydrogen content of strontium modified, uncleaned melts has been increased, particularly at 685°C. In order to study the melt hydrogen absorption susceptibility in Sr-modified alloys, the formation of different hydrogen containing compounds such as hydrides and hydroxide of modifiers and other alloying elements in Al-Si melts has been evaluated thermodynamically. It has been found that there is no hydrogen containing compound, which can form in aluminium melts, and if these compounds are introduced into the melt they will dissociated to release hydrogen.     

Kinetic parameters of interaction between hydrogen and structural defects in steel

We use the method of hydrogen permeation to study hydrogen permeation currents in 65GKh steel as functions of time under various polarization conditions. On the basis of experimental data, we find kinetic parameters of the interaction of hydrogen with defects (traps) in the metal. Experimental curves of hydrogen permeation currents are in good agreement with the theoretical curve plotted according to the general model of hydrogen trapping in the metal.Dnepropetrovsk Institute of Chemical Technology, Dnepropetrovsk. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 61–64, January–February, 1994.