Unsteady cloud cavitation mechanisms of liquid nitrogen in convergent-divergent nozzle

摘要

An investigation into the shedding mechanism of cloud cavitation is of great importance to understand the cavitation dynamics for cryogenic liquids. In this study, the dynamic processes of liquid nitrogen cavitating flows in a convergent-divergent (C-D) square nozzle under various operating conditions are experimentally investigated. Simultaneous measurements of cavity dynamics and the velocity variations in the cavitation region are implemented by introducing a high-speed camera and laser Doppler velocimetry (LDV). Several cavitation numbers are realized by changing the inflow velocity and thus the throat velocity. The specific shedding characteristics as well as the mechanism of the re-entrant jet and condensation shock are qualitatively analyzed for each case by examining high-speed photographs. In addition, a three-dimensional numerical model based on the large Eddy simulation (LES) is employed to further explore the re-entrant jet/condensation shock-dominated cavity shedding dynamics. The numerical results are in good agreement with the experimental results by comparing the temporal cavitation regime distributions and the velocity variations at the same positions. The velocity of the re-entrant jet at the end of the cavity is about ?4 to ?5m/s and decreases along the upstream direction. The re-entrant jet and the condensation shock are found to be the dominant mechanism for the shedding of cloud cavitation when σ = 0.497 and σ = 0.386, respectively. The shedding mechanism revealed by the combined experimental and numerical studies offers a deeper understanding of the unsteady shedding of cloud cavitation for cryogenic fluids.