PREDICTION OF ROTORDYNAMIC FORCES GENERATED BY LABYRINTH SEAL CLEARANCE FLOW (WHIRL, FINITE-ELEMENT, DESTABILIZING)

Labyrinth seals have been investigated to quantify the flow-induced forces generated by them in typical turbomachinery applications. The seal flow governing equations proposed in the literature have been modified to consider the seal configuration where the rotor center is at a finite eccentricity with respect to the seal center. The seal flow model accounts for the circumferentially varying flow coefficients and the kinetic energy recovery factor of the annular orifice flow across the seal fins. The continuity and momentum equations for the steady seal flow have been discretized and solved employing the Newton-Raphson's iterations to get the steady state nodal pressures and velocities. The seal cavity pressure distributions are integrated over the rotor surface to yield the radial and tangential seal forces which act along and normal to the line passing through the seal and rotor centers.; For a perturbation motion of the rotor center about an arbitrary eccentricity position, the time dependent seal flow governing equations are linearized, assuming small changes in the cavity pressures and velocities about their steady state values. The resulting linear partial differential equations have been solved to get the perturbation pressures that are proportional to the rotor center motion along two orthogonal coordinate directions which when integrated over the rotor surface yield the seal stiffness and damping coefficients. The stiffness coefficients have been verified by comparing with the seal force versus eccentricity ratio results of the seal steady flow analysis.; In addition to comparing with the published experimental results, the analytical results have been validated by carrying out expemental investigations on a model labyrinth seal test rig. Additional confirmation on the seal cavity circumferential pressure distribution has been obtained by finite element investigations of the labyrinth seal flow where the flow continuity and Navier-Stokes equations in the three orthogonal coordinate directions have been solved. In conclusion, the research presented point out the need to control the cavity circumferential flow induced by the seal inlet swirl velocity and the rotor rotation, in order to reduce the rotor whirl producing tangential force component.