THE EFFECT OF TEMPERATURE ON THE FORCED RESPONSE OF A BLISK ROTOR WITH INHERENT MISTUNING

Rotor forced response is a major cause of high-cycle fatigue (HCF) in gas turbine engines. Blade-to-blade variations in natural frequency, known as mistuning, can cause significant variations in the blade-to-blade vibrational response. Individual blade resonant response, primarily the peak frequency, has been used as a 'fingerprint' to identify a rotor blisk, and the change in frequency is widely used as a failure detection technique. The frequency data from a forced response investigation of an embedded rotor in the Purdue 3-stage axial compressor research facility is the focus of this work. The forced response of the embedded rotor was measured with both strain gauge and blade tip timing systems. During a repeatability study of the vibrational response, a notable shift in blade peak response frequency was observed. Despite a shift in the peak frequency, the overall shape of the individual blade resonant response curve remained similar, even with the inherent mistuning of the rotor. Factors affecting the frequency and dynamic response were investigated to address this shift. A major difference between these tests was the ambient temperature, which was different on different days and at different times of the day. Material properties are generally temperature-dependent, which has the potential to change natural frequencies. A cyclic symmetric FEM modal analysis showed a modal frequency shift at different temperatures. An analytical study was conducted based on the Fundamental Mistuning Model, considering the effect of temperature. The analytical results correlate well with the experimental results, showing similar blade peak response shifts without significantly changing the blade resonant response curve for the considered temperature range.