Experimental Investigation of Whirl in Self-Acting Air-Lubricated Journal Bearings

Bearing characteristics influencing the threshold speed at which large-amplitude self-excited whirl occurs in complete, air-lubricated journal bearings were experimentally investigated. Various combinations of rotors having clearance ratios, Ψ = c/r, ranging from 0.268 × 10^?3 to 2.350 × 10^?3 and symmetrical bearing assemblies having slenderness ratios, L ′ = L/D, ranging from ¼ to 1 were tested.

By varying slenderness and clearance ratios and unit load, by opening or closing supply orifices, or by adding imbalance, the whirl threshold speed could be varied between zero and the limit set by the available power.

Experimental methods of identifying the cylindrical and conical modes of synchronous and self-excited whirl are described. The whirl hysteresis region and the nature of whirl at speeds above the threshold are examined. Three methods of avoiding large-amplitude self-excited whirl are discussed.     

Calculated Performance of Non-Newtonian Lubricants in Finite Width Journal Bearings

A numerical procedure has been developed for the calculation of the performance of non-Newtonian, polymer-thickened lubricants in finite width journal bearings. Such oils were found to act as if they had averaged “anisotropic viscosities,” i.e., different viscosities in the circumferential and side leakage directions, even though the viscosity was taken to have one definite value, a function of the resultant shear stress, at each point in the oil film. Overall, polymer oils carried less load at a given eccentricity, gave less friction and a flatter pressure distribution than mineral oils of the same low shear viscosities. By analogy with the previously calculated infinite width case, which gave similar results, it is expected that the flatter viscosity temperature slope of the polymer oils will compensate for their apparent viscosity decrease. The program has also been adapted to “natural” boundary conditions, which improve upon the delineation of the cavitation region on the inlet side of the bearing.     

Externally Pressurized Journal Gas Bearings

Externally pressurized gas-lubricated bearings with multiple orifice feed are investigated. An analytical treatment is developed for a semicylindrical bearing with 9 orifices and for a cylindrical journal bearing with 192 radial and 24 axial orifices.

Experiments are described on models of the two bearing configurations with specially designed fixtures which incorporate pneumatic loading and means for determining pressure profiles, gas flow, and gap height. The correlation between theory and experiment is satisfactory.     

Performance Characteristics of Worn Journal Bearings in Both Laminar and Turbulent Regimes. Part I: Steady-State Characteristics

The effects of geometric change due to wear on the hydrodynamic lubrication of journal bearings are determined theoretically and experimentally in both laminar and turbulent regimes. The steady-state characteristics of the bearings such as film pressure, attitude angle, and Sommerfeld number are analyzed by a semianalytical finite element method for various wear depth parameters, and the theoretical results are compared with the experimental results.

It is found that the geometric change due to wear has significant effects on the steady-state characteristics in both laminar and turbulent regimes. Good agreement is obtained between the theoretical and experimental results.