Dynamic flowfield of a close-range impinging jet in a cylindrical pool

— Submerged close-range impinging jets (CRIJs) are widely applied to numerous engineering fields; however, the research on the dynamic flowfield of close-range impinging jets, especially when the impinging distance is very small, is not yet sufficient in the numerical simulation and experiment. In the present study, the time-resolved particle image velocimetry (TR-PIV) is used to measure the dynamic flowfield of an impinging jet with the impinging distance of H / D = 1. Here, H is the nozzle inner diameter and D is the impinging distance. The effects of the Reynolds number Re and the nozzle end-profile (wall constraints) on the vortex generation and migration inside and outside the gap are investigated. The obtained experimental data are further analyzed using the vorticity analysis and the proper orthogonal decomposition (POD) method. It is found that the Reynolds number affects the vortex generation and migration in different ways for nozzles with different end-profiles. The Reynolds number affects only slightly the flow pattern of the basic nozzle (nozzle I). On the contrary, the Reynolds number can strongly affect the flow pattern of the bevel nozzle (nozzle II) and dynamic vortices can appear when the value of Re increases to 1600. The dynamic vortex migration from the gap to the outside exhibits significant periodic characteristics. The vorticity analysis determines the vorticity size and distribution of the time-averaged field. Further, the energy distribution and variation in the vortices outside the gap are revealed based on the distribution of the large-scale structure of the transient field in the POD analysis. The transient pulsating velocity fields of the first four modes illustrate the abrupt and periodic characteristics of the velocity field at the microscopic time-scale.