Unsteady characteristics of liquid nitrogen cavitating flows in different thermal cavitation mode

摘要

Two kinds of thermal cavitation dynamics in varying temperature liquid nitrogen, namely the inertial mode and the thermal mode were identified in our previous work [17]. The aim of this work is to investigate the unsteady cavitation characteristics and shedding dynamics of liquid nitrogen cavitating flows in different thermal cavitation mode based on an in-house process code and the Hilbert-Huang Transform method. The experimental results show that the unsteady characteristics of different mode are significantly different. For the inertial mode, the vortex inside the cavity is significant. The attached cavity collapses immediately after detachment. For the transitional mode, the strength of vortex inside the cavity becomes slighter. The strength of the re-entrant jet becomes slighter. For the thermal mode, the attached cavity is much shorter and thinner. The re-entrant jet no longer triggers the detachment, and all the attached cavities shedding from the same position. This shedding mechanism becomes a kind of diffusion and dissipation process without obvious vortex, the cavitation process becomes significantly stable. Generally, as the temperature increases, the shedding frequency and the number of co-existing shedding processes monotonically increases; the characteristic frequencies of one single shedding process and the quasi-cycle decrease and then increase.