Impact of Foreign Object Damage on an Aero Gas Turbine Engine

This paper details the development of a prototype in-flight foreign object damage (FOD) detection system through various stages, resulting in a system capable of detecting objects as small as one gram (1g) mass. The system comprises an eddy current sensor based tip timing system and acoustic emissions vibration sensors controlled through a digital signal processor (DSP). QinetiQ have developed light weight, contamination-immune eddy current tip timing sensors for use in engine health management. Engine tests confirmed these sensors’ potential for detecting FOD events. FOD detection algorithms were developed and implemented in a prototype DSP that was built and tested on an uninstalled gas turbine engine. The trials showed that the prototype DSP FOD detection system could detect dynamic FOD events at full engine speed. Further work was carried out to enhance the FOD detection system, overcoming limitations in the previous system through the implementation of enhanced algorithms and its extension to accept four eddy current sensor inputs as well as a vibration signal input from an acoustic emissions (AE) sensor. An algorithm that computes engine speed from the tip timing data was also implemented to alleviate the need for a separate 1/rev signal. A number of engine trials were successfully completed in order to validate the system. The speed algorithm has been successfully validated on engine trials and comparisons with a conventional optical based 1/rev showed the DSP-generated 1/rev signals to be almost identical to the conventional system. Typically, the error was in the region of 0.03% speed. The investigations culminated in a test series designed to ascertain the system’s sensitivity to foreign object impacts. These demonstrated that the system was capable of detecting objects down to one gram (1g) mass introduced at low speed into the engine intake.

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Determination of Allowable FOD Defects Sizes on the Surface of Gas-Turbine Engine Stator Parts Based on Stress-Concentration Factors

Volume 7A: Structures and Dynamics ◽

10.1115/gt2014-25019 ◽

2014 ◽

Author(s):

Alexandr Pakhomenkov ◽

Denis Slobodskoy

Keyword(s):

Stress Concentration ◽

Gas Turbine ◽

Gas Turbine Engine ◽

Operational Experience ◽

Foreign Object ◽

Turbine Engine ◽

Periodic Inspection ◽

Concentration Factors ◽

Stress Concentration Factors

Requirements for reliability and safety of modern aircraft engines are constantly growing [1–2]. Among these requirements is periodic inspection of the engine condition and condition of its individual parts during operation, for the purpose of evaluation of the risk to operation. This is to ascertain possible damage to various engine parts in the course of operation and progressive wear. Damage can occur for a variety of reasons: ingestion of foreign matter in the engine gas path, operation in extreme and off-design conditions, wear, etc. To trace the engine parts condition and detect various damage on the engine parts, periodic inspection is provided. In case of any damage or deviations on parts, the question of their performance and possibility to break during operation are addressed. There are two ways of answering this question: 1 – experimental demonstration of the required strength of parts with damage; 2 – computational demonstration of the required strength of parts with damage. The first way requires a good deal of time and money for carrying out the experiments. It is efficient only with enough operational experience in typical parts with various surface damage. While developing a new engine (having no prototypes) it is more reasonable to use computational methods. To determine the allowable damage of gas-turbine engine parts, a special procedure has been developed. Its main principles consist of the following: - classification of the typical parts damage by foreign object ingestion; - determination of the stress concentration factors (Kt) due to damage for various defect sizes; - determination of strength factors of safety and life for various zones of parts without damage; - determination of Kt values with which minimum allowable values of strength safety factor and life are attained; - determination of allowable sizes of various types of damage for all zones of each part based on previously defined Kt dependencies on typical damage sizes. This methodology is proposed for determination of allowable damage on the surface of gas-turbine engines stator parts caused by foreign object ingestion in order to ensure the required reliability and safety; its experimental verification is foreseen for the future.

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