Experimental and theoretical analysis of a rigid rotor supported by air foil bearings

Abstract

-The popularity of compressors utilizing foil bearings is increasing. Their mechanical design is challenging, and an accurate prediction of the bearing coefficients is important. A mathematical model taking into account the foil structure, and the detailed geometry of a three pad foil bearing are presented. The steady state solution and dynamic coefficients are obtained through zeroth and first order perturbed equations respectively. Analysis of the foil structure reveals the importance of distinguishing between a static foil stiffness for the zeroth order equation and a dynamic stiffness for the first order equation. Calculated bearing coefficients are compared to experimental results obtained from a dedicated test rig. Generally, good agreement is observed and minor discrepancies for the damping coefficients are discussed.

Stability of rigid rotors supported by air foil bearings: Comparison of two fundamental approaches

“…The comparison between the two methods, described in this work, clearly and surprisingly indicates significant discrepancies in the prediction of the OSI. This is an important finding because the linearised frequency analysis is generally considered to be valid in terms of predicting both the linearised bearing stiffness and damping properties as well as the OSI [31][32][33][35][36][37][38][39][40][41][42]. That is, the perturbation technique proposed by Lund [28] is generally regarded to be sufficiently accurate.…”

“…In order to predict lateral vibration response and stability of rotors supported by bump foil gas bearings, linear [31][32][33][35][36][37][38][39][40][41][42] and nonlinear analyses [34,[43][44][45][46] can be carried out. In the linear analysis, the gas film forces are represented by equivalent springs and dampers.…”

A fully coupled air foil bearing model considering friction – Theory & experiment

“…The modelled test rig has previously been presented by the authors [37] and comprises a hollow shaft supported by two identical three-pad AFBs as illustrated in Fig. 1.…”

“…The excitation force amplitude was chosen to give a maximum displacement amplitude of 8 µm in both the vertical and horizontal directions, as this provided an operable signal-to-noise ratio, while the behaviour remained reasonably linear. The experimental procedure is further described in [37], while the current results are given from [55].…”

Investigation of dynamic properties of the microturbine with a maximum rotational speed of 120 krpm – predictions and experimental tests

“…Foil bearings are one of the solutions adopted in modern bearing systems for the purposes of supporting high-speed rotors [23]. Such bearings do not require an external lubrication system; air or another substance that is present in their immediate vicinity can be used as a lubricating medium.…”