Flexural vibrations of rotors immersed in dense fluids part I: Theory

Abstract

In this paper, the linear vibrations arising in rotating shafts immersed in a dense annular fluid are analyzed from a theoretical point of view. It is found that even at relatively slow rotating speeds fluid elastic forces induced by the co-rotating flow surrounding the shaft significantly affect the transverse natural modes of vibration of the shaft: each transverse mode related to the shaft at rest gives rise to a forward whirl or direct mode and to a backward whirl or retrograde mode. Linear stability of such modes is also analyzed.