Analysis & Interpretation of Nonsynchronous Whirling in Turbomachinery. J. Vance/J. D. Tison, ASME Paper 78-PET-26, 1978.

Nonsynchronous whirling is sometimes evident in the complex vibration signatures produced by high speed, highly loaded turbomachinery. Rotor dynamics analysis based on linear stability theory would indicate that nonsynchronous whirling is almost always unstable. Field experience has shown that the actual whirling motions are often bounded, thus raising certain practical questions about a proper definition of stability. This paper shows that linear stability theory can be used to predict the onset of the nonsynchronous whirling, but that the amplitudes of the bounded whirling motions are governed by the nonlinear equations, thus reconciling the mathematical models with field observations. It is also shown that the load-dependence of some nonsynchronous instabilities can be predicted by improved mathematical models.