Master thesis and internship[BR]- Master's thesis : Performance of cantilevered beam foil bearings for high speed turbomachinery application[BR]- Internship

Abstract

This thesis investigates the performance of cantilevered beam foil bearings for high-speed turbomachinery. The study provides critical insights into the rotor's dynamic behavior by utilizing a finite element-based rotor dynamics analysis tool, with experimental tests to investigate the static properties of the bearing and validate the dynamics simulation results. The research highlights the importance of selecting appropriate bearing configurations based on dynamic properties to achieve optimal rotor performance. \\

Significant findings from this research underscore the unique contribution of this thesis. The study reveals the profound impact of stiffness and damping coefficients on the rotor's natural frequencies and excitation amplitudes. The increasing dynamic stiffness, for instance, not only increases the damped natural frequencies of the rotor but also amplifies the excitation amplitude at these frequencies, leading to an earlier onset of instability in the rotor and larger vibration amplitudes. In contrast, dynamic damping generally exerts an opposing effect on rotor dynamics. However, the numerical simulation could not predict nonlinear phenomena in the rotor response, which affected the quantitative results. \

Moreover, static tests revealed that all the bearings exhibited nonlinear deflection properties relative to the applied load and were asymmetrical. It was found that there is no apparent correlation between the under-spring compliance variation and the beam's matrix density variation. The compliance depends on other factors, too. In terms of stiffness and mechanical energy dissipation, the bearing with configuration F under-spring had the least structural stiffness and highest damping coefficients.\\

While the experimental dynamic test showed good correlations with the numerical simulations to some extent, it's important to note the limitations of this research. The tests showed that the optimal design for this application was the configuration F under-spring, with its good rotor dynamics performance linked to its mechanical energy dissipation obtained in the static tests. However, further research is needed to fully understand the implications of these findings and their potential for practical application.\\

The study also proposes comprehensive guidelines for designing optimal under-spring configurations and suggests future research directions. The results underscore the significance of the gyroscopic effect and its implications for the stability and behavior of high-speed rotating machinery. This work contributes valuable knowledge to the field of aerospace engineering, particularly in the design and analysis of high-speed rotors and bearings.