Characterization of efficient tilting pad journal bearings and pivots through advanced models and experiments for design enhancement

The new generation of compressor systems for sustainable development demands from the bearings increasingly challenging operating conditions, including high peripheral speed. Tilting pad journal bearings are commonly used in turbomachinery due to their stability at high speed and low loads. An accurate characterization of the bearings is therefore of vital importance for the design of turbomachines. This thesis focused on developing new models and testing methods for the accurate characterization of efficient tilting pad journal bearings and their pivots. The research has investigated new paradigms for the computational analysis of tilting pad journal bearings, with particular emphasis on the effect of assembly and machining tolerances and of measurement uncertainties. The research has also explored the turbulent lubrication typical of high peripheral speed, formulating new criteria for the analysis of turbulent oil-lubricated tilting pad journal bearings. Central to the working principle of tilting pad journal bearings is the tilting degree of freedom given by the pad pivot. In this thesis, new theoretical models were developed to account for the effect of pivot conformity, introducing the novel concept of effective rotational stiffness for the Rocker Back pivot and a novel analytical-empirical model for the stiffness of quasi-conformal Ball and Socket pivots. Finally, new experimental results have been produced for the identification of bearing dynamic coefficients.