Investigating the influence of tool shape during FSW of aluminum alloy via CFD analysis

This paper describes the application of the CFD code, Comsol Multiphysics, to modeling the 3-D metal flow in friction stir welding of AA 2024-T3 aluminum alloy in order to investigate the influence of tool shape over the metal flow. Heat transfer and non-Newtonian flow equations were solved simultaneously. The results from the benchmark experiments found in the literature were used for validation purposes. Scrolled shoulders and threaded pins were given as kinematic boundary conditions. This made the computational problem an easy one. A welding engineer can predict the metal flow around the tool with different scrolls and threads under any welding conditions without making expensive experiments. Investigation of the velocity field before actual welding can save a lot of engineering hours.     

基于CFD的新型风幕控尘装置的模拟研究及其应用

针对传统风幕控尘装置设备多、空间小、掘进机移动不便等诸多不足之处,⌒进行了优化设计。为确保新型风幕控尘装置的实际应用效果,指导现场防尘系统设计,确定抽出式风机风筒安设位置,依(山西某矿掘进巷道工作面1:1建立了物理几何模型,并利用计算流体动力学(CFD)进行模拟。根(湍流模型特性及流体运动特点,选取拉格朗日法离散相模型对掘进巷道粉尘浓度分布进行了模拟分析并进行现场实践。结果显示,所选物理几何模型参数设置合理,拟合精度达到预测要求;加装新型风幕控尘装置前后,粉尘浓度下降对比明显;距底板2.1 m处安设抽出式风机风筒时,系统降尘效果显著。     

Erosion coupled dynamic mesh analysis for location of maximum erosion in 90-degree bends for gas-solid flows

The progressive change in the surface geometry of the component due to erosive wear affects the correct estimation of erosive wear performance and service life of the components handling particulate flows. The current study focuses on determining the change in the location of higher erosion on the bend surface during the pneumatic conveying of solids with continuous geometric modification due to erosive wear. Computational fluid dynamics (CFD) based erosion-coupled dynamic mesh methodology is adopted to simulate the time-dependent surface modification of the 90° bend geometry due to erosive wear. Available experimental data are used to validate the numerical results. Further, the erosion distribution and the location of the maximum erosion for different flow velocities, particle sizes, and bend radius ratios with the increase in solid throughput are investigated. It has been found that the modification in the bend geometry due to erosion influences the location of the maximum erosion. The increase in thickness loss due to erosion increases the variation in the location of the maximum erosion. Furthermore, an equation for predicting the location of maximum erosion of bend geometry is obtained based on the bend radius ratio and the thickness loss.     

Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.     

On the effect of wind direction and urban surroundings on natural ventilation of a large semi-enclosed stadium

Natural ventilation of buildings refers to the replacement of indoor air with outdoor air due to pressure differences caused by wind and/or buoyancy. It is often expressed in terms of the air change rate per hour (ACH). The pressure differences created by the wind depend - among others - on the wind speed, the wind direction, the configuration of surrounding buildings and the surrounding topography. Computational Fluid Dynamics (CFD) has been used extensively in natural ventilation research. However, most CFD studies were performed for only a limited number of wind directions and/or without considering the urban surroundings. This paper presents isothermal CFD simulations of coupled urban wind flow and indoor natural ventilation to assess the influence of wind direction and urban surroundings on the ACH of a large semi-enclosed stadium. Simulations are performed for eight wind directions and for a computational model with and without the surrounding buildings. CFD solution verification is conducted by performing a grid-sensitivity analysis. CFD validation is performed with on-site wind velocity measurements. The simulated differences in ACH between wind directions can go up to 75% (without surrounding buildings) and 152% (with surrounding buildings). Furthermore, comparing the simulations with and without surrounding buildings showed that neglecting the surroundings can lead to overestimations of the ACH with up to 96%.     

ZSM5-Y型分子筛催化剂复配体系裂化性能数值研究

采用流动和反应耦合模型模拟ZSM5-Y复配催化剂体系在提升管反应器内的催化裂化过程。结果表明,重油催化裂化反应主要发生在喷嘴附近,该处有45%的重油转化为汽油和柴油。对于ZSM5-Y型复配催化剂体系,ZSM5加入沸石催化剂的显然影响着汽油和液化气的产率,反应产物中柴油馏分及重油馏分的产率基本上不受影响。加入少量择形催化剂便大大降低提升管反应器汽油馏分收率,并提高液化气收率,但汽油与液化气产率显著变化仅发生在择形催化剂加量较小的时候,一旦超过10%以后,对气油和液化气的产率影响反而较小。     

Numerical solutions of unsteady flows with low inlet Mach numbers

This study deals with a numerical solution of a 2D unsteady flow of a compressible viscous fluid in a channel for low inlet airflow velocity. The unsteadiness of the flow is caused by a prescribed periodic motion of a part of the channel wall with large amplitudes, nearly closing the channel during oscillations. The channel is a simplified model of the glottal space in the human vocal tract and the flow can represent a model of airflow coming from the trachea, through the glottal region with periodically vibrating vocal folds, and to the human vocal tract.     

Low temperature co-fired ceramic (LTCC)-based biosensor for continuous glucose monitoring

This article presents design, fabrication and testing of a miniature ceramic-based biosensor which is destined for continuous glucose monitoring. It is fabricated using well known LTCC (low temperature co-fired ceramics) technology. The biosensor consists of a microreaction chamber, three thick-film electrodes and a microdialysis tube. The detection process is based on oxidation of glucose by molecular oxygen in the presence of enzyme - glucose oxidase, GOx. One of the reaction products is a hydrogen peroxide which is detected amperometrically during its oxidation at a working electrode. Computational fluid dynamics (CFD) analysis was used for optimization of the biosensor geometry and considerations of the influence of operating conditions (flow rate) on mass transfer (diffusion) of the glucose within the microreaction chamber. Tests of the developed LTCC-based biosensor indicate its linear response to glucose concentration up to 9 mM with a relatively high sensitivity of about 147 nA/mM. Moreover, the properties of the presented ceramic biosensor are compared with properties of a similar device made in silicon/glass and in Perspex^®.     

风机流场并行数值模拟在集群系统上的应用

介绍集群系统的特点及其软硬件配置环境。利用计算流体力学商用软件Fluent对一种新型垂直轴风力机风轮在曙光天潮超级服务器4000A集群上进行数值模拟及并行计算,得到风轮内外部的三维流场,实现该软件在高性能并行计算机上的应用,为并行有限元分析提供一个基础计算平台。     

SCR脱硝系统静态混合器优化布置数值模拟研究

基于CFD数值模拟技术系统地研究了静态混合器对改善SCR脱硝系统首层催化剂入口截面速度/浓度均匀分布特性的作用规律。数值计算结果表明,针对特定的静态混合器型式,优化前后速度/浓度分布偏差最大改善量分别为8.89%、12.26%,系统整体压损最大升高量约为188 Pa。因此认为静态混合器的优化布置可以显著改善截面内的速度/浓度均匀分布特性,但基于系统压损呈现的变化规律,建议在进行静态混合器设计时需综合权衡速度/浓度分布偏差改善性能与系统整体压损变化特性两方面的因素。