Determining the effect of bearing clearance and preload uncertainties on tilting pad bearings rotordynamic coefficients

Tilting Pad Journal Bearings (TPJB) are commonly used in high-speed and high-power turbomachines, due to their contributions in avoiding rotor instabilities. Studies related to the estimation of dynamic coefficients have been carried out considering nominal values of the geometric parameters (clearance and preload) for all bearing pads. However, the unavoidable uncertainties on these geometric parameters and, therefore their possible influence on the TPJB rotordynamic coefficients do not seem to have been discussed enough. In a previous work, a numerical study was conducted to examine the influence of preload and bearing clearance variations on a fivepad TPJB rotordynamic coefficient. The current work is an extension of that paper, considering at this time the Design of Experiments framework. By means of a 2k factorial design and ANOVA random effect model, uncertainties on bearing clearance and pad preload values are introduced in a standard numerical model (i.e. finite element model) used to estimate the direct and cross-coupled dynamic stiffnesses of the five pad TPJB. The influence on these dynamic coefficients, due to the variance of the aforementioned geometric parameters, is discussed and presented in graphical form in order to illustrate the sensitivity of the TPJB dynamic coefficients. Results derived from this study show that variations on loaded pads affect the direct dynamic coefficients, and unloaded pads variations influence the cross-coupled dynamic coefficients. This work contributes to the understanding of the sensitivity of TPJB dynamic coefficients to manufacturing tolerances.