Thermodynamic analysis of unsteady cavitation dynamics in liquid hydrogen

This paper presents a numerical study regarding the evolution of cavitation dynamics in liquid hydrogen cavitating flows with special emphasis on the shedding process and thermodynamic characteristics. The liquid hydrogen cavitating flows around an ogive body in different thermal cavitation modes (the quasi-isothermal mode, the transition mode, and the thermo-sensitive mode) were numerically investigated. Both 2-D and 3-D computations were compared and validated. The results show that the thermal transition of cavitation dynamics is mainly affected by the combined effects of thermodynamic effects and Reynolds number. Lagrangian methods were utilized to investigate the shedding process. When cavitation dynamics changes from the quasi-isothermal mode to the thermo-sensitive mode, the distribution of Lagrangian Coherent Structure (LCS) is closer to the ogive surface. Several vortexes exist between the LCS and the ogive surface. The free-stream liquid flows into the attached cavity because of the smaller vapor volume fraction, and the impact of the re-entrant jet on attached cavity becomes slight and finally disappears. The thermodynamic characteristics of liquid hydrogen cavitating flows were further investigated by the entropy transport equation. The analysis indicates that the distribution of entropy production rate caused by direct viscous dissipation S_pro.D becomes mushy and gets closer to ogive surface while the distribution of the entropy production rate caused by heat transfer S_pro.C is always along the liquid-vapor interphase with the increasing temperature.