On the whirl-precession suppression of overhung rotors by frontal coaxial absorbers

The whirl and precession motions of rotating machines when approaching the critical speeds should be avoided by properly planning the structural layout and the working conditions, though the rotational speed is generally imposed by the machine task and may happen to be necessarily close to some critical speed, especially in an already existing and unmodifiable machine. In this eventuality, the dynamic performance of the system could be conveniently modified by connecting other rotating passive masses that give rise to new patterns of the critical speeds for the compound system. The device that is studied here applies to the overhung rotors of many turbomachines and consists of another smaller cylindrical overhung rotor, coaxial and corotating in front of the main one, whose shaft, radius, height, and mass are properly chosen to modify the Campbell diagrams of the original machine and create the widest non-resonant range around the required working speeds. The analysis, taking into account the translational and rotatory inertia of both rotors, shows how this prefixed goal can be easily achieved. As an example, the absorber effect is studied in the very high speed range of the small turbomachines for automotive applications, finding a very wide non-resonant speed range, which turns out to be very favorable for the widely varying working conditions of these machines.