Journal Misalignment Research Articles

The Effect of Journal Misalignment on the Oil-Film Forces Generated in a Squeeze Film Damper

Squeeze film damper performance is usually assessed on the assumption that the axis of the journal is parallel to that of the bearing housing. For many practical cases, for example that of the overhung fan shaft in an aero gas turbine, these two elements are unlikely to be parallel, even when self-aligning bearings are used. In this theoretical study an attempt has been made to evaluate the effect of misalignment on the magnitude of the oil-film forces produced in a squeeze film damper bearing, and to this end a computational procedure has been established. From the results reported in this paper, it has been clearly shown that the effect of misalignment in a two-land, squeeze film damper can lead to a significant increase in the transmission of unbalance force through the oil film, As an example, data from a previously reported investigation into the performance of a simple two-bearing model with a single centrally supported disk have been used in a typical calculation. The results from this computation indicated that the oil-film forces generated, could have been several times greater than those calculated on the assumption that the journal and bearing housing were parallel. Unfortunately, there do not appear to be any clear guidelines to lay down to the designers of squeeze film dampers at this moment, in relation to journal misalignment. In general, the effect of misalignment is strongest when the ratio of land-length to radial clearance is greatest, when large unbalance is being accommodated, and when the orbit size is large. In our own analytical studies, the effect of misalignment is allowed for whenever the angle of misalignment is greater than 0.0005 radians.

Performance Characteristics of Flared Bearings

The paper offers an analysis of finite journal bearings having an axially variable clearance. Such bearings are encountered either as a consequence of manufacturing errors and wear, or as configurations specifically designed to accommodate journal misalignment. The Reynolds equation is solved for the appropriate boundary conditions and film geometry by finite difference methods. Tables of computer solutions and a number of graphs provide the performance characteristics of misaligned bearings for a wide range of parameters. The results show that striking advantages can be achieved by the use of flared bearings for cases of moderate and severe journal misalignment.

Paper 5: The Effect of Journal Misalignment on the Performance of a Journal Bearing under Steady Running Conditions

A method of solution is described in which the governing equation is modified to account for variations in the oil-film thickness in the axial direction owing to journal misalignment. The position of the journal is specified by means of its eccentricity at its mid-length and by two parameters defining the extent and direction of the misalignment. The pressure distribution is evaluated numerically, and the direct load, friction torque, oil flow, and couple arising from the misalignment of the journal are obtained by numerical integration. A full range of journal misalignment conditions is examined for two length-diameter ratios. Results are presented in the form of non-dimensionalized graphs, showing the variation of direct load and misalignment couple with the journal misalignment parameters described. The angle between the line of action of the misalignment couple and the load line is evaluated in each instance, and graphs are presented to show the variation of the performance parameters for a particular degree of misalignment with the direction of application of the couple. Results for the particular instances in which the couple is in line with or at right angles to the load line are extracted, and these are compared with published experimental results of other workers. Good agreement is obtained, and moreover it is shown that, in general, these are not the two extremes of misalignment. For these two conditions design charts are presented, whereby, from knowledge of the applied couple and direct load, the degree of misalignment and the resultant peak pressure parameter may be determined. Charts which illustrate the reduction in load capacity for a particular journal misalignment in the plane of the load are also presented. General validity is claimed for this method of exploring a relatively unexamined subject, and the results are considered by the authors to be a useful improvement on those obtained by previous analytical workers.

A Solution for the Finite Journal Bearing and its Application to Analysis and Design: II

This second in a series of papers is a continuation of the work described in Part I. Performance curves for β = 360°, 180°, 120° and 60° bearings are given for L/D values of 1/2 and 1/4 thereby extending the solutions to encompass both the L/D ratios and bearing arcs most widely used in practice. A problem illustrating the effect of L/D ratio on journal misalignment shows that the shortest bearing is not necessarily the one most capable of tolerating the maximum misalignment.