近距离淹没冲击射流动态流场特性

近距离下淹没冲击射流具有重要的应用前景，但有关其动态流场特性的研究尚不充分。利用粒子图像测速技术（Particle image velocimetry，PIV）对冲击距离为H/D=1时的动态流场特性进行测量，研究雷诺数Re和喷嘴端面轮廓（壁面约束）对间隙内旋涡生成的影响，并对试验数据进行涡量分析与本征正交分解方法（Proper orthogonal decomposition，POD）分析。结果表明，雷诺数Re对不同喷嘴端面轮廓（壁面约束）的旋涡生成和迁移影响规律不同。雷诺数对直角型喷嘴的双涡环模式流态影响较小，但对圆角型喷嘴卷吸流态影响较大，且随雷诺数的增大流场出现动态对称涡旋，该对称涡旋逐渐向间隙外迁移且呈现出明显的周期性变化特征。涡量分析得到时均场的涡量大小与分布情况，通过与POD分析中瞬态场的含能大尺度结构分布相结合，揭示间隙外涡旋能量的来源与变化规律。通过前4阶瞬态脉动速度场重构，可以从微观时间尺度进一步说明瞬态速度场的突变性与周期性。研究成果将有助于加深对冲击射流本质的理解。

Dynamic Flow-field Characteristics of Close-range Submerged Impinging Jet

Submerged impact jet at close range has important application in many fields,but the research on the dynamic flow-field characteristics is not yet sufficient. Particle image velocimetry(PIV) is used to measure the dynamic flow-field characteristics of impinging jet when the impact distance is H/D=1. The effects of Reynolds number Re and the nozzle end-profile (wall constraints) on the vortex generation and migration inside and outside the gap are studied. The experimental data are analyzed by vorticity analysis and proper orthogonal decomposition(POD) method. The results show that the Reynolds number has different effects on the vortex generation and migration of different nozzle end profile (wall constraint). The Reynolds number has little effect on the flow pattern of the double vortex ring mode of the right-angle nozzle,but has a greater influence on the flow pattern of the round angle nozzle,and the dynamic symmetric vortex appears with the increase of the Reynolds number. The symmetrical vortex gradually migrated out of the gap and exhibited obvious periodic variation characteristics. The vorticity analysis obtains the vorticity size and distribution of the time-averaged field. By combining with the distribution of the energetic large-scale structure of the transient field in the POD analysis,the source and variation of the vortex energy outside the gap are revealed. By the reconstruction of the first four orders transient pulsating velocity field,the abrupt change and periodicity of the transient velocity field can be further explained based on the microscopic time scale. This result is helpful to deepen the understanding of impingement jets.