An Efficient Iterative Approach for the Analysis of Thermal Instabilities in Rotating Machines

Most of the technological developments achieved in the turbomachinery field during the last years have been obtained through the introduction of fluid dynamic bearings, in particular tilting pad journal bearings (TPJBs). However, even those bearings can be affected by thermal instability phenomena as the Morton effect at high peripheral speeds. In this work, the authors propose a new iterative finite element method (FEM) approach for the analysis of those thermal–structural phenomena: the proposed model, based on the coupling between the rotor dynamic and the thermal behavior of the system, is able to accurately reproduce the onset of thermal instabilities. The authors developed two versions of the model, one in the frequency domain and the other in the time domain; both models are able to assure a good tradeoff between numerical efficiency and accuracy. The computational efficiency is critical when dealing with the typical long times of thermal instability. The research activity has been carried out in cooperation with General Electric Nuovo Pignone SPA, which provided both the technical and experimental data needed for the model development and validation.