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. © 2020 Journal of Mechanical Engineering.