In order to study the flow characteristics and sealing properties of single phase and two-phase cavitation flows under typical working conditions,the numerical simulation of cryogenic floating ring seals with transitions was carried out,and the features of pressure distribution of rotor face,axial and circumferential direction in the seal clearance were compared and analyzed.The effects of inlet pressure,inlet temperature,eccentricity and speed of rotor on leakage rate,flow loss coefficient,seal force and angle of displacement under single phase and two-phase flow conditions were investigated.The results show that under concentric state,the flow fields of single phase flow and two-phase flow are symmetrical.Under eccentric state,the pressure at larger clearances is lower than that at smaller ones in single phase flow,but greater in the vicinity of seal exit when two-phase is applied,resulting in a lower extent of cavitation near the larger clearance.The leakage rate and seal force both increase as rotor speed decreases or inlet pressure and eccentricity increase,and the characteristic values of two-phase flow are lower than those of single phase flow.The leakage rate and seal force both increase as inlet temperature drops in two-phase flow,while the corresponding values of single phase flow are not affected by the change of temperature.The angle of displacement of single phase flow is little affected by the changes of various parameters,indicating the direction of seal force is always in close proximity to the position of minimum clearance.While the fluctuation of the angle of displacement of two-phase flow is relatively large,and it intends to intensify with the increase of inlet temperature.The inlet flow loss coefficient of single phase flow increases slightly as eccentricity decreases or inlet pressure and rotor speed increase,while the inlet flow loss coefficient of two-phase flow is more sensitive to the changes of various parameters.