三元催化转化器内部流场的数值模拟

Numerical simulation for the internal flow of the three-way catalytic converter

随着计算机技术的发展,数值模拟已经成为研究三元催化转化器的重要手段。本文在考虑冷态流场分布及将尾气看作空气做湍流的基本假设下,运用数值模拟软件FLUENT,采用四面体混合型网格,选取k-￡模型、多孔介质模型和质量入口等边界条件,建立了三元催化转化器的物理与数学模型,对三元催化转化器内部流场进行了数值模拟研究,获得了其内部压力场、湍动能及速度场的分布状况。研究结果表明,在扩压管附近、收缩管内壁和衬垫外壁之间均形成涡流区;三元催化转化器出口处速度场急剧变化,造成能量较大损失,因此要注重三元催化转化器扩压管与收缩管锥角的设计。随后运用所建立的模型对不同扩压管与收缩管长度下的三元催化转化器内部流场进行模拟,得出该工况下最优的三元催化转化器尺寸为收缩管长21 mm,扩压管长33 mm,并验证该尺寸下三元催化转化器工作状态较优。

With the development of computer technology,numerical simulation has been an important means of researching three-way catalytic converter.Under the hypothesizes of considering cold flow field and recognizing exhaust as air,a numerical simulation model and a physical model of the three-way catalytic converter were built with the help of FLUENT.The internal flow of three-way catalytic converter was simulated by selecting tetrahedral hybrid grid,k-ε model,porous media model and boundary conditions such as mess-flow-inlet.The distribution of resulting pressure field,turbulence kinetic energy and velocity field in the three-way catalytic converter show that eddy current regions are formed nearby the diffuser tube and between in wall of the collapsible tube and outside wall of the gasket.Velocity field dramatically changes at the outlet of the three-way catalytic converter,which results in large energy loss.Consequently,it should be paid special attention to the cone angle design of diffuser tube and shrink tube for the three-way catalytic converter.Given different lengths of the diffuser tube and the shrink tube,internal flow field of three-way catalytic converter were simulated.The optimal structure of the three-way catalytic converter was obtained.The optimal length of shrink tube and diffuser tube were 21 mm and 33 mm,and the comparatively better working condition of the designed sizes was verified.