Identifying the causes of excessive vibration in gas turbine engines in the course of their rig tests

Examples of identifying the causes of high vibration of engines during rig tests based on many years of experience in evaluating the vibration behavior of gas turbine engines are presented in the paper. Defects such as slippage of the outer bearing support, failure to comply with the geometric parameters of the hydrodynamic damper with elastic rings and the conditions of oil feeding, unsatisfactory laying of the engine on the engine frame, rubbing of individual elements of the rotors, their wedging and rotational stall are diagnozed. The practice of using  modern methods of processing and analysis of vibration processes that makes it possible to optimize the amount of subsequent work with the engine is shown, with the above-mentioned defects taken as an example. A standard technique for diagnosing the causes of excessive vibration in gas turbine engines using the most efficient methods of signal processing is proposed on the basis of the experience gained. In case of detecting high vibration by bench vibration measuring apparatus we propose to install additional vibration sensors with the registration of vibration in the frequency range of up to 30 kHz parallel to the standard vibration sensors. This is  followed by sequential data processing with obtaining autospectrums in speed and acceleration, calculation of the cospectrum, the spectrum of highs, the envelope spectrum, cascade demodulation on the basis of highs, multiple iterations of the cascade demodulation procedure. The effectiveness of the proposed method has been confirmed by many years of its practical use and can be applied both in the conditions of the test bench and in operation for the evaluation of the  engines’s health.