Abstract: Dual plane balance theory of rotor dynamics is introduced, the distributed Alford forces in multilevel seals are done to be equivalent on two end planes of cylinder, and an identification model of dynamic coefficients for multilevel seals is set up. The mixed movement of translation and oscillation occurring on cylinder is considered in this model, and cylinder resonance is used to enlarge the influence of Alford force，thus improving the identification accuracy is accordingly enhanced. An experiment rig for seal dynamic characteristics is constructed to research the influences of inlet/outlet pressure ratio, rotating speed, eccentricity and clearance on dynamic coefficients. Results show that eight stiffness damping coefficients increase obviously with the growth of inlet/outlet pressure ratio, and coupling effects exist in vertical and horizontal directions. The cross-coupled stiffness and direct damping coefficients increase with rotating speed, but the direct stiffness and cross damping coefficients have no obvious change. The cross-coupled stiffness coefficient in eccentric state is greater than that in concentric state, but the direct damping coefficient decreases, which means that the seal-rotor system in eccentric state is easier loss of stability than in concentric state. With the decrease of average clearance of seal, the absolute values of eight dynamic coefficients increase.

Key words: Dynamic coefficients, Seal, Vibration