Test Results for Sawtooth-Pattern Damper Seals: Leakage and Rotordynamic Coefficients

Abstract

Test results consisting of direct and transverse force coefficients are presented for eleven, sawtooth-pattern, damper-seal configurations. The designation “damper” seal refers to a seal which uses a deliberately roughened stator and smooth rotor, as suggested by von Pragenau [1], to increase the net seal damping force. The designation “sawtooth-pattern” refers to a stator-roughness pattern whose cross section normal to the axis of the seal resembles saw teeth with the teeth direction opposing fluid motion in the direction of shaft rotation. The sawtooth pattern yields axial grooves in the stator which are interrupted by spacer elements which act as flow constrictions or “dams.” Sawtooth-pattern seals had more damping than smooth seals but less than the round-hole-pattern seals tested previously. Stiffness of sawtooth and round-hole-pattern seals were comparable. Leakage of maximum-damping configurations was greater for sawtooth-pattern than for round-hole-pattern seals; both types of seals leaked substantially less than did smooth seals. If damping is sacrificed, sawtooth-pattern seals can be designed to leak less than round-hole-pattern seals.