Numerical and Experimental Investigation of Gas Turbine Rotor for Early Fault Detection

Rotodynamic analysis is a key analysis for turbomachinery for investigating the health and integrity of equipment. Most of the analyses are performed at the design stage, while the actual machine behavior is different due to imperfections like unbalance, misalignment, cracks, and so forth. In this paper, a representative CAD model of a gas turbine rotor is developed to get the actual rotodynamic response of a rotor. Vibration data of the rotor is compared with that of the developed numerical model. The reference model representation of the actual machine in terms of critical speed and vibration value is found to be 99.7% and 99.1%, respectively. Rotodynamic analyses of numerical models are performed for early identification of faults under various scenarios of unbalance, crack, and crack with unbalance. For these scenarios, modal analysis and harmonic analysis are performed. Natural frequencies and vibration behavior are utilized to capture the variation that indicates the presence of a fault. This way, early identification of faults is made to save the machine from damage. Within the unbalance range of ${1.0\times 10}^{-9}$ to 0.5 kg, a direct relation between change in unbalance mass and vibration amplitude is observed in the case of unbalance and unbalance with crack. Similarly, for cracks (of 1–3 mm thickness and depth up to 372 mm), a shift in maximum vibration amplitude frequency to first critical speed from second critical speed is noted. Hilbert transform is utilized to track the nonlinearity especially up to an operating speed of 3000 rpm (50 Hz). These key outcomes can be used to reduce rotary machine downtime by not only highlighting the problem at a very early stage but also swiftly identifying its root cause for the smooth working of rotary equipment in the industry.