Reduced-Order Modeling and Wavelet Analysis of Turbofan Engine Structural Response due to Foreign Object Damage (FOD) Events

Abstract

The development of a wavelet-based feature extraction technique specifically targeting FOD-event induced vibration signal changes in gas turbine engines is described. The technique performs wavelet analysis of accelerometer signals from specified locations on the engine and is shown to be robust in the presence of significant process and sensor noise. It is envisioned that the technique will be combined with Kalman filter thermal/health parameter estimation for FOD-event detection via information fusion from these (and perhaps other) sources. Due to the lack of high-frequency FOD-event test data in the open literature, a reduced-order turbofan structural model (ROM) was synthesized from a finite-element model modal analysis to support the investigation. In addition to providing test data for algorithm development, the ROM is used to determine the optimal sensor location for FOD-event detection. In the presence of significant noise, precise location of the FOD event in time was obtained using the developed wavelet-based feature.

A Foreign Object Damage Event Detector Data Fusion System for Turbofan Engines

“…The data fusion process presented in figure 1 was applied to simulated data from a combined-effects gas path/vibration model of a large turbofan engine. 14,33 The event occurs at cruise conditions under multivariable closed-loop control, demonstrating the fusion system's ability to differentiate between conditions resulting purely from the FOD event and those due to the response of the controller. Figures 12 through 14 present the bpa determined by a) the vibration expert, b) the gas path expert, and c) the result of the fusion of the two using Yager's modification to Dempster's rule of combination.…”

“…Also, analytical structural models of aircraft engines, such as Finite Element Models (FEMs), are typically computation-time intensive due to the vast amounts of time-dependant spatial data they produce, and do not lend themselves for direct application to diagnostic system development and testing. 14 imbalance after manufacturing 20 which is also included in the reduced order structural model for a "steady state" response. The FOD-event depicted in figure 4 produces no permanent imbalance (structural damage).…”

“…The exact time of the event is precisely determined using this technique. Indeed, the event is modeled by imposing a pulse whose magnitude is a function the of foreign object impact characteristics presented in Turso, 14 on the fan disk. The two spikes shown in figure 8 result from the rising and descending parts of that pulse "filtered" through the mechanical (i.e., rotor-bearing) system.…”

“…Figure 1 provides an overview of the fusion system. The vibration data-driven portion of the system utilizes a wavelet-based algorithm developed as part of the work presented in Turso et al 14 Selected features are extracted from the gas path analysis and the engine's vibration monitoring system and assessed via two fuzzy inference engines respectively, each providing a "possibility" distribution for FOD event occurrence. The inference engines (or "experts" used in the present context) assign degrees of membership to these features, which are subsequently transformed into basic probability assignments for the gas path and vibration components, and are fused via Dempster's combination algorithm.…”

A Review of Vibration Monitoring as a Diagnostic Tool for Turbine Blade Faults

“…Mechanical and Electrical Technology IV with high sensitivity to the crack depth. James et.al [26] reported that precise locations of the FOD event in time could be achieved using the developed wavelet analysis method. Al-badour et.…”