基于动态模态分解的缸内流场演变及动能分析

采用高速粒子图像测速技术(particle image velocimetry,PIV)测量了一台直喷式光学发动机的缸内流场,利用动态模态分解(dynamic mode decomposition,DMD)算法,提取了发动机从进气冲程早期到压缩冲程后期中出现的多尺度涡团结构,量化了涡团的比动能在整个冲程阶段的衰减程度。结果表明:从进气冲程早期开始,缸内流场主要由低阶DMD模态表现的大尺度流场结构和高阶DMD模态表现的小尺度涡团结构组成;DMD模态的比动能变化可清楚地反映从大尺度流场结构到小尺度涡团的能量级联和耗散过程。同时还发现,与压缩冲程相比,进气冲程期间的流场可形成更多小尺度的涡团结构,并表现出更快的能量衰减特征,且该阶段流场能量衰减现象对发动机转速更加敏感。

Kinetic Energy Analysis of In-Cylinder Flow Evolution Using Dynamic Mode Decomposition

In this investigation, high-speed particle image velocimetry (PIV) was used to measure the flow fields in a gasoline direct injection optical engine under motoring condition. The dynamic mode decomposition (DMD) algorithm was used to extract the multi-scale flow structures from early intake stroke to late compression stroke. The decay process of specific kinetic energy of modes during both strokes was quantified. The results show that from early stage of intake stroke, the in-cylinder flow fields are mainly composed of large-scale flow structures represented by low-order DMD modes and small-scale vortex structures rep-resented by high-order DMD modes. The variations of specific kinetic energy clearly reflect the energy cascade and dissipation process from large-scale flow structures to small-scale structures. Compared with compression stroke, the flow fields during intake stroke show a faster energy decay process with more small-scale flow structures. The energy decay of the intake stroke is more sensitive to engine speed.