液体火箭发动机高速涡轮泵轴端动静结合型机械密封端面液膜受低温、高速、高压等极端工况影响极易产生气液两相流现象；诱发两相流的机制及相变对密封的影响规律尚不明确，亟需发展相关的仿真模型并开展实验验证工作。以某高速涡轮泵用动静结合型螺旋槽机械密封为研究对象，基于Laminar层流及Mixture多相流模型，开展了低温、高速等极端工况下密封间隙内流体的空化相变特性研究；以泄漏量、开启力与内部气相体积占比等性能参数为表征指标，分析了该类密封在液氮介质环境工况参数对两相流动特性和相态转变的影响规律。结果表明随着密封间隙增加将导致两相流在有限约束范围内的体积增大，较弱的动压效应导致内部压力产生较小变化进而使得空化相变能力减小；气相体积占比随着液膜温度的增加而增大，随着密封介质压力的增加而减小。开展了低温实验研究，并验证了仿真模型的正确性，理论与实验结果将有助于深入理解低温高速动静结合型机械密封两相流机理，对可重复高速涡轮泵的运行可靠性和稳定性提升具有重要的实践价值。

The non-contact mechanical seal of high-speed turbopump in the liquid rocket engine operating under harsh conditions such as low-temperature， high-speed， and high-pressure， is easy to produce gas-liquid two-phase flow. The mechanism of inducing two-phase flow and the effect of phase transition on seal performance are still unclear， so it is urgent to develop relevant theoretical models and perform experimental test. Based on Laminar flow and Mixture multiphase flow models， this research， taking a non-contact hydrodynamic spiral groove mechanical seal of high-speed turbopump as the object， studies the cavitation phase transition characteristics of fluid in the seal gap under low temperature high-speed harsh conditions. The main seal performance parameters， such as leakage， opening force and proportion of internal gas phase volume， are obtained， and the influence of the working parameters on the two-phase flow characteristics and the phase transition process with the low temperature liquid nitrogen as the sealed fluid is analyzed. The results show that with the increase of the film thickness， the volume of the fluid in the sealing gap increases， and the dynamic pressure effect decreases，which leads to a small change in the internal pressure， and therefore， reduces the cavitation phase transition possibility. With the increase of the film temperature， the proportion of internal gas phase volume increases， and decreases with the increase of inlet pressure. A series of low-temperature experimental tests are carried out， and the correctness of the theoretical models is verified. The study will help to understand the two-phase flow mechanism of low-temperature high-speed non-contact mechanical seal， which has important engineering value for improving the operational reliability and stability of reusable high-speed turbopump.