Numerical investigation of thermo-sensitive cavitating flows in a wide range of free-stream temperatures and velocities in fluoroketone

Abstract

The objectives of this paper are to validate an existing numerical modeling framework for fluoroketone and investigate the dynamic evolution of thermo-sensitive cavitating flows. The cavitating flows around a NACA0015 hydrofoil with chord length Co=50.8mm and angle of attack α0=10deg in a wide range of temperatures and velocities in fluoroketone are numerically investigated. Three thermal parameters, including nominal temperature drop ΔT∗, thermodynamic parameter Σ and C-factor, are applied to assess the thermodynamic characteristic of fluoroketone. It is found the thermodynamic effects on cavitating flows for fluoroketone at 373K and nitrogen at 83.06K are similar under the same reference cavitation number and Reynolds number. It indicates thermal parameters C-factor could accurately predict the extent of thermodynamic effects. General agreements are obtained between the numerical results and the experimental measurements, including the pressure distribution and cavity structures. The numerical results show that there are two typical cavitation dynamics in varying temperature fluoroketone under the same free-stream velocity and cavitation number. As the free-stream temperature increases, cavity area increases to the maximum at the transition temperature and then decreases, the dominant frequency significantly increases when the temperature reaches its transition point. Further analysis indicate that the liquid/vapor density ratio D dominates the change of the cavitation dynamics when temperature is below the transition temperature, and the cavity tends to be mushier and longer with the increasing temperature during this temperature range. However, the thermodynamic effects, which could suppress the development of the cavitating flow, dominate the change of the cavitation dynamics when temperature is above the transition temperature. For free-stream velocity U∞=9.6m/s, which has been experimentally investigated in the reference experiment, the transition temperature for thermo-sensitive cavitation is 318K (±2K) and the maximum temperature drop ΔTmax is approximately 0.82K under this condition. For varying free-stream velocity, the increasing velocity could suppress the thermodynamic effects, and hence the transition temperature increases with the increasing velocity under the same flow conditions.