Experimental data are presented for the threshold of whirl instability for a rigid rotor supported in externally pressurized air-lubricated journal bearings.
One of the most severe difficulties encountered in the application of air-lubricated journal bearings is their tendency to be unstable or to produce instability of systems in which they are components.
The effects of supply pressures from 1 Kgf/㎠ to 5 Kgf/㎠ and radial loads from 0.83 Kgf to 2.83 Kgf with constant rotor mass on the threshold of whirl instability are discussed for three type of bearing configurations, circular, 3-lobe and 4-lobe.
Radial loads were applied to the rotor by electromagnet. Circular bearing has inside diameter of 40 mm and is 40 mm long. Noncircular bearings have length of 40 mm and are Length/Diameter = 1. Rotor has length of 190 mm.
We show that the bearings are more stable with increasing load at constant supply pressure, and that there is a region where the bearing stability is increased with decreasing supply pressure at constant load.
In this experiment the modes of all of the self-excited whirl are not always the same mode, and whirl instability threshold speed of noncircular bearings are not always high that of circular bearing. At high supply pressure circular bearing is more stable than noncircular bearings. Whirl ratio is increased with increasing load.
