Analysis of phase transition behavior and optimization of groove structure of mechanical seal for deep-cooling medium in turbopumps

To enhance the sealing performance of the turbopump in aerospace deep-cooling medium thrusters， a phase change model for fluid-solid-thermal coupling based on the modified Reynolds equation was developed. This model comprehensively incorporates the temperature-pressure effect to address the challenges associated with phase change behavior in the non-contact mechanical seal end face medium， while ensuring high service performance. By considering the maximum opening force， minimum leakage， maximum stiffness， and maximum liquid-phase volume rate of the seal as optimization objectives， an overall expectation function was established. A multi-objective optimization analysis was then conducted on the structural parameters of the end shallow groove using the response surface method. The accuracy of the model was verified through experimental validation. Results indicated that the phase change of liquid hydrogen medium inside the seal end face is significant， with the density decreasing from 68.9 kg/m3 at the inlet to 0.19 kg/m3 at the outlet， in which the groove structure of the end face influences the magnitude of the liquid-phase volumetric rate of the medium and the seal performance. The optimal parameter combination for the shallow groove structure of the seal end face was found to be 12 grooves， a 6 μm groove depth， a 14° helix angle， a 0.66 groove width ratio， and a 0.4 groove dam ratio. This configuration reduced the leakage rate by 10.69%， increased the liquid-phase volumetric rate by 11.18%， improved the opening force by 0.58%， and enhanced stiffness by 6.89% compared to the pre-optimization state.