Gas Turbine Diagnostics: Signal Processing and Fault Isolation

Abstract

Diagnostics of gas turbine engines is important because of the high cost of engine failure and the possible loss of human life. In this book, we will focus on aircraft or jet engines, which are a special class of gas turbine engines. Typically, physical faults in a gas turbine engine include problems such as erosion, corrosion, fouling, built-up dirt, foreign object damage (FOD), worn seals, burned or bowed blades, etc. These physical faults can occur individually or in combination and cause changes in performance characteristics of the compressors, and in their expansion and compression efficiencies. In addition, the faults cause changes in the turbine and exhaust system nozzle areas. These changes in the performance of the gas turbine components result in changes in the measurement parameters, which are therefore dependent variables. This chapter introduces some basic concepts that are necessary for an understanding of gas turbine diagnostics. First, the importance of signal processing in noise removal from measurements is highlighted. Next, the typical gas turbine diagnostic process is explained. The widely used linear filters and the median filter are then introduced. This is followed by an outline of the least-squares approach and the Kalman filter. Finally, the role of influence coefficients and the basics of vibration-based diagnostics are highlighted.