喷油器瞬态两相流动的建模方法

为了研究柴油机喷油器内部的气穴现象,采用一种新的方法建模并进行瞬态两相流动的数值模拟. 首先求解针阀开启时刻的稳态流场,然后导入自编的程序进行瞬态流场的计算. 自编程序是基于Fluent提供的用户自定义函数,用于控制模型边界条件,分析针阀受力情况和计算其运动速度. 初始计算条件来自稳态流场,每一步瞬态计算都依赖之前流场的计算结果. 这种建模方法保证了数值模拟的连贯性和真实性,确定喷油器初始条件就可以完整地计算喷油过程,得到每一时刻喷油器内部的压力分布和两相流分布等数据. 研究结果表明,这种新的建模方法是可行和有效的,其数值模拟结果和实验结果相吻合,并能揭示出喷油器喷嘴入口处气穴现象的产生、发展和消失过程,是进一步深入开展柴油喷油系统两相流动特性研究的一种新的途径.

Method of modeling transient two-phase flow in injector

A new method was applied in modeling and numerical simulation in transient two-phase flow inside a diesel injector for cavitation study. The simulation was started in steady flow when the needle valve was just about to be lifted and then contined to compute unsteady flow with self-made program. User define function(UDF) provided by Fluent was used in definition of boundary condition, force analysis of needle valve and computation of its speed. The initial condition was from steady flow field then every unsteady computation was decided by former flow field. This method assured numerical simulation consistent and authentic. It is possible to simulate the whole fuel injection with injector's initial condition and get statistics of pressure and phase volume fraction distribution at any time inside an injector. Simulation results are close to experiment results and it evidences that this new modeling method is valid and reliable. Cavitation commencement, expansion and disappearance are revealed during fuel injection. This modeling method provides a new way to further study two-phase flow inside diesel injection system.