Abstract: A dynamic analysis model for cylinder-seal system is set up, and a new identification method for fluid-induced forces and stiffness coefficients in seals is presented. The pressure distribution and the generation mechanism of tangential fluid-induced forces are analyzed based on the two-control-volume model in eccentric seals. The theoretical studies show that the pressure distribution is sinusoidal approximately, and the angle of high pressure points deviation from the minimum clearance is increasing along the axis. The system stability decreases with the increasing cross-coupled stiffness in a certain range. Beyond this range, the system will be destabilized. Influences of rotating speed, inlet pressure, eccentricity and clearance on fluid-induced force are tested in the rig. It is found that a large tangential fluid-induced force is produced in the direction perpendicular to the eccentric displacement of rotor. The differences between the tangential and radial fluid-induced forces become larger and larger with increasing rotating speeds. Under the action of the forces, the logarithmic decrement of the cylinder descends with increasing rotating speeds, and the system stability decreases.

Key words: Flow-induced vibration, Fluid-induced force, Seal, Stiffness coefficients, Two-control-volume