An experimental investigation of wind-induced ovalling oscillations of thin, circular cylindrical shells

A series of wind-tunnel tests have been conducted on the ovalling oscillations of closed-ended, thin cylindrical shells such as silos. Variations of the ovalling frequency and amplitude with increasing flow were measured with a variety of elastic cylinders. The threshold flow velocities at which ovalling oscillations abruptly occurred were examined with respect to the circumferential mode numbers of oscillations. Cross spectral analysis of the pressure fluctuations on a rigid cylinder revealed a convective nature of the pressure field. On this basis, a mechanism for the onset of ovalling oscillations in relatively higher circumferential modes was proposed; the possibility of the mechanism was confirmed by experimental results on the threshold of ovalling oscillations. Furthermore, it was found that the occurrence of ovalling oscillation alters the characteristics of the pressure fluctuations on the cylinder to a great extent, even if the amplitude is quite small.