Abstract
Test results are presented involving axial rubbing of a test rotor with an overhung disk to investigate test results cited by Den Hartog [1]. Point rubbing was introduced via a rod on the inside (motor-drive side) and outside faces of the overhung disk for multiple operating conditions (running speeds below and above the critical speed) and multiple shaft configurations. For supercritical running speeds, no change in the response spectrum was observed. For subcritical running speeds, a slight increase of response at twice running speed was observed.
“Face” axial rubbing was introduced by forcing a contact between the outside face of the disk and a flat surface. Rubbing at running speeds below the critical speed produced: (i) a small backwards component at the running speed frequency, (ii) a large backward-whirl component at twice running speed, and (iii) a very large, twice-running-speed, forward-whirl component. Rubbing at running speeds well above the critical speed produced a subsynchronous forward component near the critical speed. The large twice-running-speed results due to rubbing at the outside face were comparable to Den Hartog’s. However, point rubbing on the inside face did not produce the subsynchronous backward-whirl response cited by Den Hartog.
Analysis of a nonslipping kinematic whirl condition (comparable to classical dry friction whipping) for the face of an overhung disk against a stationary surface predicts reverse asynchronous whirl; however, testing over a wide range of parameters failed to produce this response. None of the present test results produced the types of very high vibration levels and grave consequences that have been produced in test rigs for conventional, radial dry-friction whirl and whip.
