Turbine Engine Health/Maintenance Status Monitoring with Use of Phase-Discrete Method of Blade Vibration Monitoring

Abstract

The intended aim of the paper was to present a short review of more than 15 years of experience of ITWL in the field of applying the signal of actual rotational speed (aperiodic and oscillation components thereof) to the expert diagnosing of aero-engines, including identification of low- and high-cycle fatigue (LCF, HCF) of critical structural members. What has been presented is some essential metrological bearings of the non-contact technique of measuring the engine’s rpm with some flexible key phasors (i.e. vibrating compressor/turbine blades). Also, methods of numerical analysis of measuring signals, in use nowadays, have been discussed. With the jet engine of the SO-3 type (in use on the TS-11 “Iskra” combat trainer) as an example, are discussed algorithms of both the identification of disadvantageous aeromechanical effects (energy state of the engine - i.e. the source of accelerated HCF wear of structural components) and the early detection of symptoms of fatigue failures to compressor blades and the bearing system. The discussed problems have been illustrated with examples selected as to emphasise practicalities of applying a new source of diagnostic information to ‘actively’ control the process of fatigue wear (HCF + LCF) of engine components and to forecast the engine health/maintenance status.

Inductive sensors for blade tip-timing in gas turbines

“…However the method can be used in a monitoring system to track changes of vibration frequency. It is confirmed that the fundamental frequency decreases when a fatigue crack is initiated and developed [11], [13], [17]. …”

“…The following sections discuss analysis methods of TOA signal we use in single or dual sensor systems. Many of presented concepts were implemented in the software of SPL-1b system in mid 1990s' [11], [17].…”

“…It also introduces significant uncertainty into vibration measurement. In some cases it is possible to make it redundant using reference signal derived from tip-timing sensors [11], [18]. Alternatively, TOA data from different tip sensors can be analysed in pairs as differential deflections [20].…”

“…Several tailored designs have been developed for sensing compressor and turbine blades made of ferromagnetic and non-ferromagnetic materials, offering resolution about 20um. They were applied in:  All stages of compressor and turbine of SO-3 turbojet [11][13] [17]  Fan stage of K-15 turbojet  Military turbofan -fan, compressor, HPT, LPT [7]  1st stage of Spey turbofan tested in spin pit in Patuxent River [14]  Industrial fan in the desulphurization system in a convention power plant [16] Inductive sensor is the first choice technology for health monitoring applications due to long life, high reliability and resistance to contamination.…”

Application of Blade-Tip Sensors to Blade-Vibration Monitoring in Gas Turbines

“…They were successfully employed in monitoring system for blade vibration, which was developed in Poland for turbojet training aircrafts (Szczepanik & Witoś, 1998;Witoś & Szczepanik, 2005). It is the first airborne tip-timing system implemented worldwide and is still in use by Polish Air Forces.…”