Experimental Analysis of Cracked Turbine Rotor Shaft using Vibration Measurements

The gas turbine rotors are subjected to different types and directions of loading like axial, bending, shear and thermal loading. This loading is changed periodically during the operation which can lead to crack initiation in the rotor shaft. When these cracks propagate to the extreme limit, it will lead to sudden failure of the shaft rotor. Crack existence can be detected by observing the vibration parameters of the rotor, the vibration parameters is changed when the shaft is cracked. The most observable change in these parameters is the natural frequency and the response of vibration. In this study, the vibration of gas turbine rotor is studied with the existence of cracks and without them. The rotor was modelled experimentally. A test rig was built to model the real rotor. During the experiments, the rotor speed range was variated from zero to 10000 rpm. Two crack depths of 0.2 and 0.4 of the shaft radius were modeled in addition to the uncracked shaft. The behavior of the results of the vibration parameters was compared with other previous research and was closely similar. When the rotor was intact, the critical speed is (7900) RPM and the acceleration response is (10.291) m/s2. When a crack is fabricated deeply (0.2R) the critical speed decreases to (7750) RPM and the acceleration response increases to (11.5043) m/s2. When the crack depth increases to (0.4R), the critical speed was less (7500 RPM), and the acceleration response increased more to (12.4429) m/s2.