A Methodology for Dynamic Coefficients and Nonlinear Response of Multi-Lobe Journal Bearings

Abstract

A methodology for prediction of dynamic coefficients and nonlinear simulation of multi lobe bearings is developed. This simple formulation that is an extension of Reason and Narang (1982) approach. An easy to implement finite perturbation method is used to evaluate stiffness and damping coefficients. In order to obtain the fluid film forces, the oil film pressure generated in the bearing is solved using a semi analytical pressure model. Four multi lobe journal bearings, namely: two-axial groove, elliptical, three-lobe and offset bearings are studied in terms of non dimensional stiffness and damping coefficients. The parameters are: L/D ratios of 0.5 and 1.0, pre-load factor of 0.5 and offset factor of 0.5; except for the offset bearing, for which the offset factor is 1.0. The results are provided in graphical form and compared with existing numerical techniques. All the coefficients show the influence of Sommerfeld (long) bearing solution at high eccentricity ratios. Results also indicate the applicable range of reciprocal relationship combining the Ocvirk (short) and Sommerfeld bearing solutions for all multi lobe bearing configurations. The journal center trajectories obtained are compared with numerical results and the effect of stability on rotor bearing system is studied for both balanced and unbalanced rotor. It is concluded that the approximate bearing solutions which are predominantly applied to cylindrical bearing configuration, can also be successfully implemented for noncircular profiles.