Abstract
A robust approach to investigate a tilting pad journal bearing (TPJB) as a whole tolerance stack-up assembly is presented. Normal component variation within actual design tolerances is considered. The vector loop is expanded via Taylor series for sensitive analysis. The bearing shell and tilting pad machined radiuses for each pad are found to be the more influential dimensional characteristics on the assembled clearance and preload. A leading edge relief (LER) was used to avoid unloaded pads fluttering, while maintaining a satisfactory bearing assembled clearance in the loaded pads throughout the resultant preload variation. Pivot flexibility and preload loss due to pad wear in service life were included in the preload variation assessment. Surface response multivariate multiresponse models were built for a 4-pad TPJB under load between pad (LBP) and load on pad (LOP) configurations. Desirability functions rendered the maximum and minimum rotordynamic coefficient and tribological parameter responses across speed. The LOP configuration showed more variation in the direct rotordynamic coefficients, while the LBP configuration indicated more sensitive cross-coupled coefficients with very strong sign change in some cases. Among the tribological performance parameters, the eccentricity and pad maximum pressure were more affected, followed by the minimum film thickness, and weakly by the power loss, and oil film temperature. The dispersion of the tribology parameters under normal manufacturing variation is found of importance. Four, and seven extreme geometrical state cases were identified for the LBP, and LOP bearing configurations, respectively.
