Instability of an over-hung rigid centrifuge rotor partially filled with fluid

The objective of this paper is to experimentally investigate the instability of an over-hung rigid centrifuge rotor partially filled with fluid. Specific attention is paid to the developing process of rotor instability, the dynamical behaviour of rotor system while the instability occurs, and the whirling frequency and direction of rotor system within the unstable region. The effects of the fluid fill ratio on the whirling frequency, the unstable region and the rotor imbalance are also studied. The results clarify some issues and show many new phenomena about the instability of the rotor partially filled with fluid for the first time. The phenomena include the sub-synchronous frequency that does not result in the instability of rotor system and which disappears in the unstable region at the large fluid fill ratios; different whirling frequencies existing in the unstable region between the slowly increasing and decreasing rotational speed operations, hysteresis phenomenon in the upper side of the unstable region and the breaking-down phenomenon of the fluid free surface.