Ovalling oscillations of cantilevered and clamped-clamped cylindrical shells in cross flow: An experimental study

Abstract

Some experiments on cantilevered, thin cylindrical shells in cross flow are presented, as well as experiments with shells clamped at both ends and spanning the wind tunnel test section. Ovalling oscillations were found to occur mainly in the second, third, fourth and fifth circumferential modes of these shells, in both first and second axial modes, for both types of support condition, the critical mode numbers depending mainly on shell geometry. Contrary to previous tests, it was found that at the onset of ovalling, the vortex shedding frequency was not always an integral sub-multiple of the ovalling frequency of the shell—although an integral relationship (or nearly so) was found to exist more often than not. In the experiments with clamped-clamped shells, careful study was made of the power spectral densities of both the wake signal, measured by a hot wire anemometer, and the shell vibration signal, measured by a non-obtrusive fibre optics probe; the modal damping in various modes of the shell was also measured.