Rotordynamic Analysis for Integrally Geared Air Compressor Using Measured Dynamic Coefficients of Tilting Pad Journal Bearings

Abstract

Dynamic characteristics of a tilting pad bearing strongly depend on the direction of applying load as well as the magnitude. As the bearing load of geared compressor are determined by aerodynamic forces of impellers and mesh forces of helical gears in accordance with operating speed, dynamic coefficient of each bearing also varies with respect to rotor speed. Hence, in order to ensure rotordynamic stability of geared compressor, accurate estimations of bearing loads and corresponding dynamic characteristics of tilting pad bearings in accordance with operating speeds are highly requested. In this study, bearing dynamic test rig was developed based on floating bearing housing design, with speed range from 3000 to 32,000 rpm. In order to precisely estimate lateral critical speeds and the stability of pinion rotor of integrally geared compressor, the experimental investigation has been carried out on five pads tilting-pad journal bearings of 45 mm in diameter. Static eccentricities of the tilting pad bearings were investigated with various load directions and corresponding dynamic characteristics were also obtained. Multi-frequency excitations have been used to evaluate the nature of frequency dependency of the bearing dynamic coefficients. Using experimentally identified dynamic coefficients of rocker-back type tilting pad bearing with respect to rotating speed, rotordynamic analysis of gear-driven pinion rotor was carried out and compared with shaft vibration measurement. The predicted rotor behavior showed good agreement with measured one.