Diagnosing turbine engine bearing structures with the aid of FAM-C and FDM-A methods

Abstract

The diagnostic method FDM-A [2], based on the measurement of the pulsation component frequency modulation, and the FAM-C method, making use of the alternating current frequency, were developed in the Air Force Institute of Technology. The essence of their accuracy consists in “natural” synchronisation of the sampling signal with the angular velocity of the observed kinematic links. These methods make it possible to determine the level of wear of a subsystem and its location during normal operation of the power unit. They provide opportunities for determining numerous parameters of bearings, bearing structures, and the rotor unit. Moreover, the FDM-A method makes it possible to detect resonances in particular elements and their parameters - among others, they provide opportunities for assessing the level of the mechanic quality factor of the examined structure, i.e. the time margin of structure operation until the structure reaches the state of resonance. On the other hand, the FAM-C method provides opportunities for defining numerous parameters of the phenomena connected with the rotor unit. The diagnostic system is connected to an arbitrary point of the electric network (electric junction, for instance) supplied with the direct voltage¹ or the alternating voltage² taken from the generators driven by the examined rotating system. The presented experimental material was recorded in operating investigations of the aircraft turbine engine unit, in which the role of “generators – observers” was played by: an aircraft DC generator and a threephase AC rate generator. Generators of this type are also used in rocket cutters with turbine engines, this way the conclusions presented in the article can be easily transferred to those objects. During the measurements, performed on the decks of the examined airplanes and on engine test beds, the ranges and locations of assembly and wear defects were determined. Successive stages of wear of the rolling bearings were also observed.