Transient Response Analysis of High-Speed Rotor With Different Bearing Interface and Their Trade-Off

Abstract An aircraft and/or helicopter typically includes an auxiliary power unit (APU). The APU is used to supply electrical power to systems and components while the aircraft is parked on the ground, in flight, and during aircraft taxiing or landing. In some applications, the APU also provides the bleed air to the main engine. The APU is generally comprised of a compressor, which is operatively connected to a generator directly or indirectly via gear box (GB) to drive it. The generator produces the electrical power required to drive the systems and components. In cases where a critical speed of the high-speed rotor is present near to the operating range, it is not desirable to operate at or near this mode due to adverse impacts to the life of bearing, rotor, and APU component vibratory fatigue. There are number of solutions available to change the critical speed. In this paper, the Transient response analysis of high-speed rotor for the APU/GB were performed for the different interface between bearing and housing, which are as follows: (a) Air gap between ball bearing and housing at driving end. (b) Air gap between ball bearing and housing at non driving end, (c) O-ring between ball bearing and housing at both ends, (d) Tolerance Ring between ball bearing and housing at both ends, (e) Wire Mesh Dampers between ball bearing and housing at both ends, and (f) Squeeze film damper at driving end of bearing. The goal of this paper is to provide the Campbell diagram and nonlinear transient response analysis of the above-mentioned interfaces. The final selection of the above interface is based on the margin from the operating speed range and transient response analysis. In addition, sensitivity of stiffness housing was performed to achieve at least +15% critical speed margin away from the operating speed range.