Thermally Induced Whirl of a Rigid Rotor on Hydrodynamic Journal Bearings

An experimental study was conducted on rigid rotors supported on 360° circumferentially grooved journal bearings. The effect of bearing clearance, lubricant inlet temperature, and supply pressure on whirl instability was examined. The experimental results indicate that self-excited whirl exists whenever the lubricant inlet temperature is higher than that of the bearing surface. On the other hand, when the bearing temperature is higher than the lubricant inlet temperature, whirl does not occur even at rotor speeds considerably higher than the instability threshold predicted by isothermal hydrodynamic theory. This thermally-induced whirl phenomenon has not been reported elsewhere and is documented in this paper. While the conditions giving rise to this phenomenon are unlikely to occur in the steady-state operation of high-speed bearings, they can exist under transient conditions. The findings of this study also provide strong evidence of the importance of thermohydrodynamic effects in considerations of stability of journal bearings.