The cryogenic liquid fuel launch vehicles always encounter longitudinal unstable vibration during flight as serious threat to the normal operation of the rocket. It shows typical low-frequency characteristics and often occurs in the jet condensation process of cryogenic liquid oxygen in propellant pipelines. To solve this problem from the source

the characteristics of jet condensation oscillation and flow pattern transition must be investigated. Based on the height function method

a modified mass transfer model was used to capture the interfacial curvature dynamically. The relationship between the condensation pulsation frequency and two-phase interfacial curvature was established and the frequency of pressure oscillation was found to be 9.8~10.6 Hz. The results show that there are three typical types of jet condensation oscillation: stable pulsation

gas plume oscillation and suck-back flow. The pressure amplitude of suck-back and oscillation flow is up to 130 kPa

while that of stable pulsation is only 1 ~ 3 kPa. By the dimensional analysis

the transition threshold of flow pattern is Jc* = 7.3 when the dimensionless structure parameter L* = 2.2. When Jc* > 7.3

the suck-back oscillating flow pattern will appear. The dimensionless criterion can predict the condensation flow pattern precisely. It provides theoretical basis and technical support for the design of cryogenic liquid fuel rocket.