Research Papers: Gas Turbines: Structures and Dynamics

Pre-emptive Rotor Blade Damage Identification by Blade Tip Timing Method

[+] Author and Article Information
Siddhartha S. Guru

Gas Turbine Research Establishment (GTRE),
Defence Research & Development
Organization (DRDO),
Bengaluru, India
e-mail: siddharthaguru@gtre.drdo.in

S. Shylaja

Bengaluru, India
e-mail: shylaja@gtre.drdo.in

Sunil Kumar

Bengaluru, India
e-mail: sunilkumar@gtre.drdo.in

Ramesh Murthy

Bengaluru, India
e-mail: rameshmurthy@gtre.drdo.in

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 13, 2014; final manuscript received February 3, 2014; published online February 27, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(7), 072503 (Feb 27, 2014) (4 pages) Paper No: GTP-14-1026; doi: 10.1115/1.4026802 History: Received January 13, 2014; Revised February 03, 2014

The blade tip timing (BTT) method uses the differential arrival timings of the blades at case-mounted sensors to effectively characterize the vibrations of all blades in a rotor. This paper studies the use of the BTT method for pre-emptive prediction of rotor blade damage; through a careful monitoring of blade natural frequencies in conjunction with the blade tip position during an engine test. In the current study, the low pressure turbine stage of a developmental aero engine is instrumented with a combination of eddy current and optical sensors located circumferentially on the casing. This instrumentation effectively captures the engine order resonances of interest for the blade bending mode. During one of the normal engine tests, one of the blades in the LPT stage suddenly showed a drop in natural frequency beyond the allowable scatter and an abrupt change in the blade tip position. As the engine test was continued further, this drop in blade natural frequency and change in blade tip position progressively increased towards blade failure limits. Suspecting a propagating crack in the particular blade, the test was aborted and the engine was withdrawn for detailed inspection. Inspection of the rotor blades confirmed the presence of significant aerofoil crack in the suspect blade.

Copyright © 2014 by ASME
Topics: Engines , Blades , Rotors
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Fig. 1

Sensor location looking from the engine aft

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Fig. 2

Lean at different rpm in a single run

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Fig. 3

Lean at idle rpm for various runs of a healthy rotor

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Fig. 4

Individual response seen by different sensors

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Fig. 5

Normalized scatter in blade frequencies

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Fig. 6

Monotonic change in blade lean for blade no. 67

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Fig. 7

Campbell diagram for blade no. 67




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