4气门DISI汽油机缸内湍流场POD分析

POD Analysis on In-Cylinder Turbulent Flows in a DISI Gasoline Engine

应用本征正交分解(POD)方法对一台4气门直喷式汽油机(DISI)缸内冷态湍流流场试验测量数据以及大涡模拟计算数据进行了分析,以深入考察该汽油机缸内湍流场拟序结构特性以及湍流场循环变动特性.结果表明,POD方法可以将流场湍流涡团结构按照含能数量进行分解,大尺度拟序结构和小尺度随机脉动涡团可以被有效分离,为研究其各自的形成与演化特征创造了条件.考察各模态的时间系数在不同周期间的统计变化规律,可以了解流场湍流结构的循环变动特性.相比较使用传统相平均方法来研究汽油机循环变动,POD方法可以单独研究不同能量涡团结构的循环变动特点,为进一步深入理解循环变动特性奠定基础.

Proper orthogonal decomposition（POD）method was used to analyze the PIV measurement data and large eddy simulation results of the in-cylinder cold-state turbulent flow in a four valve DISI engine, for deeply understanding the characteristics of in-cylinder turbulence coherent structures and cycle-to-cycle variations （CCV）. Computational results show that POD method can decompose the turbulence flow ac- cording to their energetic behavior, and it can effectively distinguish large scale coherent structures and small scale stochastic vortexes, providing a basis for studying their evolution rules separately. Moreover, by examining the inter-cycle change in the time-dependent coefficients for each spatial mode, CCV characteristics of in-cylinder turbulence structure is captured. Compared with traditional phase average method in analyzing CCV, POD method can provide more detailed information based on the separated vortex structures, which provides the basis for further understanding of CCV.