A published history of rotordynamic instability problems with centrifugal compressors is documented from the literature. Established theory for computerized stability analysis is reviewed, and the use of cross-coupled stiffness and damping coefficients to represent destabilizing forces is explained. A derivation of cross-coupled stiffness coefficients for torquewhirl is presented. Experimental measurements made on a simple test rig with a radial-vaned impeller are described, which show that a working fluid can exert destabilizing forces on such an impeller. These forces must be considered, in addition to journal bearing and internal hysteresis excitations, if accurate predictions of rotordynamic instability thresholds are to be made. Several classifications of these forces are hypothesized.

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