高速水润滑机械密封的两相流热振动现象

处在高速、快速启动、低黏度介质润滑下的低温高速涡轮泵轴端机械密封性能与常规密封的性能发生了显著的变化，主要因素在于高速的振动影响、低黏度介质下的较差润滑性。以水为模拟介质，研究了低黏度介质下高速机械密封的运转性能，特别是气液两相流问题，实验过程中发现了两相流介质诱发的热振动问题，其机理可能在于受压缩有限空间内的流体可压缩性的变化导致。测试结果表明，在水润滑升速工况下，机械密封虽能够保持好的密封性能，但其性能变化规律较为复杂；在接触端面从接触到非接触状态的转变过程以及稳定运转过程中均存在两相流状态，密封端面温升和摩擦力存在明显的低频振荡，温度振荡可达30℃；出现汽化两相流的情况下，理论计算的结果与试验结果在升速时误差可达到50%以上。随着密封闭合力的增加，密封会出现明显的两相流现象，相变引起的温度和摩擦力的振荡可归结为一类流体密封的自激振动现象。

Two-phase flow thermal vibration phenomenon of high-speed water-lubricated mechanical seal

Due to the high-speed vibration and the poor lubricity at low-viscosity, the performance of the mechanical face seal for the next-generation high-speed transient-startup cryogenic turbopump is significantly different from that of the conventional mechanical seal. Using water as the low-viscosity sealed fluid, the performance of the seal is tested, focusing on the gas-liquid two-phase flow. The mechanism of the induced thermal vibration may be ascribed to the transient change of the fluid compressibility within the limited space. The experimental results show that under high-speed water-lubricated condition, while the mechanical seal can maintain a good sealing performance, the pattern of the performance change is more complicated. The two-phase flow phenomena occur in both the transition processes of the seal from the contact to non-contact state and the stable running state,, and the low-frequency oscillations of the temperature and friction of the seal pairs are significant. The amplitude of temperature oscillation can reach 30 ℃. When the vaporized two-phase flow occurs, the error between the theoretical and experimental results even reaches 50%. With the increase of the close force, the two-phase flow phenomenon between the seal gaps appear more significantly. The oscillation of temperature and friction caused by phase transition can be attributed to a self-excited vibration of the mechanical face seal.