Blades in a turbine rotor synchronize their individual vibrations after a certain period of time. Each blade has a slightly different natural frequency due to manufacturing errors, and it responds individually to external excitations. Nevertheless, after a period of time the blades synchronize and vibrate at the same frequency due to weak interactions between them. In this work, experiments are reported that identify blade synchronization. Individual blade vibrations were measured simultaneously under different conditions. Measurements were made with accelerometers attached to the tip of each blade which were very light in comparison with the mass of the blade. The blades were first excited by an impact force and the natural frequencies were identified. Then, the blades were excited by airflow and individual blade-tip vibrations were recorded at several subsequent time intervals. Synchronization is analyzed through the correlation between the time responses of every blade. The correlation was calculated at each of these intervals and the results were plotted in maps. It was found that the synchronization evolves as a function of time; it is high after a medium time period and reduced at longer time periods. Thus blade synchronization presents a long wave variation that could be a source of a very low frequency vibration. It was also possible to say that synchronization is dominated by the structure of the rotor.

This content is only available via PDF.
You do not currently have access to this content.