排序方式: 共有154条查询结果,搜索用时 0 毫秒
21.
Current numerical models of gas metal arc welding (GMAW) are trying to combine magnetohydrodynamics (MHD) models of the arc and volume of fluid (VoF) models of metal transfer. They neglect vaporization and assume an argon atmosphere for the arc region, as it is common practice for models of gas tungsten arc welding. These models predict temperatures above 20 000 K and a temperature distribution similar to tungsten inert gas (TIG) arcs. However, current spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to TIG arcs they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapour and which is in a very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the work piece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapour in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2000 to 5000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, and the evaporation rate relative to the wire feed. Finally the model predictions are compared with the measuring results of Zielińska et al. 相似文献
22.
Numerical simulations have been carried out for large scale hydrogen explosions in a refuelling environment and in a model storage room. For the first scenario, a high pressure hydrogen jet released in a congested refuelling environment was ignited and the subsequent explosion analysed. The computational domain mimics the experimental set up for a vertical downwards release in a vehicle refuelling environment experimentally tested by Shirvill et al. [6]. For completeness of the analysis, an analytical model has also been developed to provide the transient pressure conditions at nozzle exit. The numerical study is based on the traditional computational fluid dynamics (CFD) techniques solving Reynolds averaged Navier-Stokes equations. The Pseudo diameter approach is used to bypass the shock-laden flow structure in the immediate vicinity of the nozzle. For combustion, the Turbulent Flame Closure (TFC) model is used while the shear stress transport (SST) model is used for turbulence. In the second scenario, premixed hydrogen-air clouds with different hydrogen concentrations from 15% to 60% in volume were ignited in a model storage room. Analysis was carried out to derive the dependence of overpressure on hydrogen concentrations for safety considerations. 相似文献
23.
运用CFX模拟分解炉模型内的流动、煤粉燃烧、CaCO3的分解过程,对系统进行气体组分质量平衡和热量平衡计算,结果表明:O2的相对误差<3%,CO2的相对误差<9%,热量的相对误差<9%,表明用CFX模拟分解炉时的可靠性达90%以上;当计算参数如CaCO3量或煤粉量变化0.01%时,炉内温度分布、出口温度、CaCO3分解率等变量几乎没有变化,而当计算参数的变化量大于0.01%时,计算结果就看出变化,即CFX的模拟计算结果响应这两个计算参数变化的灵敏度可达到近万分之一。 相似文献
24.
25.
26.
27.
28.
29.
30.
注塑成型中,熔体在模腔内的流动为非牛顿流体在复杂型腔内的非等温、非稳态流动。充填过程的三维数值模拟能更真实地模拟熔体在型腔内的三维流动状态。本文采用有限元分析软件ANSYS CFX进行二次开发,实现注塑成型充填过程的三维模拟,可求解熔体前沿、压力场、温度场等一系列模拟结果。模拟结果与注塑成型软件MOLDFLOW结果进行对比,验证了该方法的有效性。算例分析结果表明,对于薄壁制品,基于中面模型的注塑成型模拟方法是适用的,但对于非薄壁制品,采用三维模拟方法可以得到更合理更全面的信息。 相似文献