Thermal transition and its evaluation of liquid hydrogen cavitating flow in a wide range of free-stream conditions

The objectives of this paper are to (1) validate the present numerical modeling framework for liquid hydrogen cavitating flow, (2) investigate the dynamic evolution of liquid hydrogen cavitating flows in a wide range of free-stream conditions and (3) propose a thermal parameter to evaluate and predict the transition process of two typical cavitation dynamics in thermo-fluids. The dynamic evolutions of liquid hydrogen cavitating flows in a wide range of free-stream conditions (T_∞ = 14–33 K, U_∞ = 63.9 m/s, 90 m/s, σ_∞ = 0.38, 0.8, 1.2) are numerically investigated. General agreements are obtained between the numerical results and the experimental measurements, including the pressure distribution, temperature drop as well as the cavity structures. The results show that the cavitation behaviors near the triple point are similar to cavitating flows without thermodynamic effects. Two typical cavitation dynamics named the quasi-isothermal mode and the thermo-sensitive mode in liquid hydrogen are observed under the same cavitation number and flow velocity. When the free-stream T_∞ is below 30 K (T_N ≤ 0.85), as the temperature increases, the cavity area increases to the maximum around the thermal transition temperature and then decreases when the cavitation dynamics transits from the quasi-isothermal mode to the thermo-sensitive mode. Further analysis indicates that the thermal transition temperature for liquid hydrogen is approximately at T_∞ = 17 K and the transition temperature slightly increases with the increasing free-stream velocity and cavitation number. When the free-stream T_∞ is above 30 K (T_N > 0.85), the thermodynamic effects significantly decrease due to the suddenly changed physical properties. And then, the cavitation dynamics turns from the thermo-sensitive mode to the quasi-isothermal mode with the increasing temperature. The modified C-factor including both the thermodynamic effects and the effects of turbulent pressure fluctuations proposed in this paper could quantitatively evaluate and predict dynamics transition from the quasi-isothermal mode to the thermo-sensitive mode in thermos-fluids cavitating flows. It could be utilized as a parameter to design the operating conditions for thermos-fluids apparatus or system to avoid the maximum cavitation aggressiveness around the thermal transition temperature.