Effect of bump structural friction on the performance of bump foil bearing and rotor dynamic behavior: Experimental study

Air foil bearings are a kind of self-acting lubricated bearing, which have potential applications in high-speed turbomachinery. Air foil journal bearings have simple structure that consists of top foil, bump foil, and bearing sleeve, and use gas as working fluid. However, the relative motion of top foil and bump foil, bump foil and bearing sleeve occurs when dynamic pressure is generated as long as there is spinning of shaft. Thus, the friction between each part of bearing should be considered when modeling. Many papers have theoretically shown the effect of Coulomb friction between top foil and top foil, bump foil and bearing sleeve on the static and dynamic performances of air foil journal bearing by developing many bump foil structural models. The results show that this foil structural Coulomb friction can significantly make bump foil stiffer. However, the improvement of the Coulomb friction effect through experiments is quite difficult and there is no study regarding this so far. The purpose of this paper is to certify the Coulomb effect on bearing performance by using experimental method. Two bump foil journal bearings are manufactured with different bearing sleeve surface roughnesses. Foil structure stiffness, bearing lift-off speed, and rotor dynamic behavior supported by two sets of bearings are measured and compared.