Calculating the critical flutter speed of the fan blade

Igor Voytenko, Valentin Chygryn, Yuriy Torba

Abstract


The tendency to create modern gas turbine engines requires shortening the development time, which includes: design, manufacturing, and finalization. Developers strive to reduce the cost of finalization, which involves changes in design and associated refinement costs. Special attention is given to the major engine design elements, such as the fan, compressor, and turbine. There is a tendency to develop algorithms to predict phenomena that exclude the resonant and unstable modes of operation of engine design elements at the design stage. This can significantly reduce the cost and time of conducting and reduce the work on strain gauging, including: dissection, purchase, and connection of special equipment, such as the current collector of strain gauge signals. Consequently, it can also reduce the time and cost of conducting engine field tests, with potential repetitions after the anticipated design modifications. In this article, some developments are suggested, assuming the development of this type of prediction during the design stage. According to the numerical modeling results, the natural frequencies of the bending and torsional vibrations of the bandaged fan blade above the bandage flange were determined. The obtained results correlate well with the modeling results for the vibrations of the blade ring assembled with the disk. In addition, the natural frequencies were confirmed by the results of acoustic testing, and the occurrence of increased stresses on them was demonstrated by strain gauging and the use of alternative methods in full-scale engine tests. By calculating the critical flutter speed of the fan blade and its dependence on the relative flow velocity of the peripheral section of the blade profile and the relative velocity at the radius of the bandage flange, the possibility of self-oscillations of the blade feather section above the bandage flange of the bending-torsional flutter type at any external perturbations in the operating mode was determined.

Keywords


self-oscillation; turbofan engine; critical flutter speed; natural frequencies

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DOI: https://doi.org/10.32620/aktt.2024.4sup1.15