ABSTRACT
In rotating machines, there are a number of small annular clearances, which separate the rotor from the stator. Interstage neck or wearing rings are employed in centrifugal pumps between impellers. A balance drum in pumps or a balance piston in centrifugal compressors counteracts the overall axial thrust. Tip leakage in axial compressors or turbines is considered to generate a cross-stiffness, which may lead to instability. An estimate of the magnitude of the cross-stiffness that can arise is given by Alford [5]:
~ 4 -----------------~~ -· • i ~ 3 c ,~, -------------r.--1 2/ ;;:;; --------
Figure 11 Comparison oflow-frequency forced response and bearing instability in a boiler feed pump.
