Rotordynamic System-Level Effects of Three-Lobe Journal Bearings Including Manufacturing Variations

This paper examines the impact of pad-to-pad manufacturing variations in three-lobe journal bearings on system-level rotordynamics. Two sources of non-uniform clearance were studied: dissimilar pad clearance and preload. Both were varied independently within standard manufacturing tolerances. The results show that the conventional assumption that all pads having equal clearances at tolerance extremes does not capture worst-case conditions. Instead, specific non-uniform pad combinations caused the most significant amplification factors and the lowest stability margin. By applying a Surface Response Design of Experiments (SRDOE) method, surrogate models were developed to represent the nonlinear influence of the pads’ dissimilarity. The models identified the most critical combinations of pad and journal variables, revealing that industry-standard practice does not provide the most adverse system behavior. Worst-case conditions arise from non-uniform pad geometry: SRDOE models predict critical combinations, while uniform assumptions of industry-based standards underestimate risk. Incorporating realistic manufacturing variability in rotordynamic models provides a more reliable basis for turbomachinery design.