TL05 - A Resonance Condition Encountered in a Shop Overspeed Machine Due to Inertia Effects--The Theoretical Basis and Practical Experience

Abstract

This lecture will discuss the dynamic instability theory and resulting vibration characteristics of a high-speed rotor system when the ratio of the polar moment of inertia and transverse moment of inertia approaches a value of one. Impeller overspeed testing is a likely place for these inertia values to converge. An example is provided for a 51-inch (1295 mm) diameter centrifugal impeller operating in an overspeed vacuum pit at 5,780 RPM at a tip speed of 1294 ft/sec [394 m/sec]. After a methodical, stepwise, testing campaign, the problem was corrected by redesigning the rotor system to produce an inertia ratio less than 0.70. This lecture discusses the theoretical basis for this phenomenon, compares the results of the rotor dynamic simulations with overspeed vibration test data and provides an approach for assessing the level of risk for the occurrence of this instability as a function of inertia ratio.