基于大涡模拟的小型转子发动机缸内湍流研究

Investigation on Small Rotary Engine In-cylinder Turbulent Flow Based on Large Eddy Simulation

本文应用大涡模拟的方法对小型转子发动机的缸内流场进行了三维数值分析,分别从拟序结构、湍流脉动和湍动能三个方面研究小型转子发动机缸内的瞬态湍流特征。计算结果表明,大涡模拟结合Q准则可以有效的识别小型转子发动机缸内流场的大尺度拟序结构。进气过程中高强度的涡团主要分布于燃烧室的前部和后部,压缩过程中高强度的涡团分布从燃烧室中部向后部转移。湍流在垂直于转子截面上的法向脉动最为剧烈,其中中部区域的剧烈程度远高于两侧。湍流在平行于前后端面的截面上的法向脉动最弱,没有明显的波动。从进气口打开到压缩上止点期间,缸内亚网格湍动能和平均气流速度出现两次明显的峰值,这分别与进气能量和大尺度涡团的破碎有直接的关系。

In this paper,large eddy simulation(LES) is adopted to investigate the 3D flow characteristics of a small rotary engine,including turbulence fluctuation,turbulent kinetic energy and coherent structure.Three sets of conclusions based on computational results are obtained.First,by using LES coupled with Q-criterion,large scale coherent structures are identified well.It is found that high intensity vortices are distributed in the leading and trailing of the chamber in the intake process and move from the central to the trailing region in the compression process.Second,fluctuating velocities in cross section perpendicular to rotor surface shows drastic fluctuation in normal direction.In these cross sections,fluctuating velocities near the central region are relative higher.Velocities in cross sections parallel to the covers have no obvious fluctuation.Third,at the period from the intake open to top dead center,subgrid turbulent energy and mean gas velocity occurs two obvious peaks,which are related to the intake energy and break of large scale vortices,respectively.