SYNCHRONOUS ROTOR VIBRATION DRIVEN BY FLUID FORCES FROM A GEOMETRICALLY IMPERFECT LABYRINTH SEAL

The radial force acting on a rotor, due to an asymmetric pressure distribution inside the seal gland, generated from a slightly non-circular single gland labyrinth seal rotating inside a circular outer casing is investigated theoretically. A fluid mechanical lumped parameter model for the flow in and out of the seal as well as the flow around the gland in the seal is developed. The model includes first and second knife imperfections as well as rotating gland depth variations. Knife non-circularity on the rotor may be due to manufacturing tolerances or defects from in service wear damage. An appropriate solution technique for the coupled one-dimensional equations is presented. Results from this model are presented that indicate these fluid induced forces are comparable in magnitude to those generated by a rotating unbalance under some conditions. Considerations for design are given for avoiding synchronous vibration problems due to non-circular labyrinth seals.Copyright © 1995 by ASME