圆周进气对流掺混流动研究

Study on opposed mixing flow in circumferential intake

为了研究纯径向向心涡轮出口对流撞击掺混流动组织结构,采用大涡模拟对圆周进气的对流掺混流动进行了数值仿真,并用本征正交分解(POD)方法,提取和分析了不同阶模态下的流动结构。结果表明:在水平截面,底部中心形成一个滞止区,两侧壁面附近均存在一个回流区,且流动是近似对称的;在剪切力作用下,沿流动方向,旋涡结构的不稳定性增强,上游三维涡环结构逐渐拉伸、膨胀,破裂为复杂的涡辫或发卡涡结构,这增强了掺混,从而使得流体间的动量和能量交换增强;POD结果中第1阶模态所占的能量权重最高,表明脉动场中的大部分能量主要集中在此模态,此模态中的流动结构为主要流动结构。

For studying the structures of opposed mixing flow at the outlet of radial centripetal turbine,large eddy simulation was used to simulate the convective mixing flow of the circumferential intake. Flow structures in different modes were extracted and analyzed by the proper orthogonal decomposition(POD) method. The results showed that there existed stagnation zone near the bottom center and a recirculation zone near both sides of the wall,and the flow was approximately symmetrical at the horizontal cross section. The instability of the vortex structure was strengthened due to the effect of the shear force along the streamwise direction. Furthermore,the upstream three-dimensional vortex ring structure was stretched and expanded,breaking into a complex vortex braid or hairpin vortex structure,which enhanced the mixing,and also the momentum and energy exchanged between the fluids. The POD results showed that the first mode had the highest energy weight,indicating that most of the energy in the pulsating field was concentrated in this mode,and the flow structure in this mode acted as the main flow structure.