Supersonic flutter of circular cylindrical shells subjected to internal pressure and axial compression.

Results of recent experiments on the flutter of circular cylindrical shells in the Mach number range 2.5-3.5 are presented. Three shells with radius-to-thickness ratios of 2000 were subjected to radial external pressure loadings and to combinations of axial compressive loading and internal pressurization while in the presence of an external, axially-directed supersonic flow. Small amounts of internal pressurization were very stabilizing with respect to flutter, but moderate amounts reduced stability to the unpressurized level. However, high internal pressures completely stabilized the shells. . The axial compressive loading was slightly destabilizing for moderate amounts of internal pressurization. The flutter modes (which were standing waves in the axial direction with zero, one, or two circumferential nodal lines) contained many waves around the circumference (of the order of 20) that traveled in the circumferential direction. This circumferentially traveling wave phenomenon possibly results from the nonlinear nature of cylindrical shells. Model integrity was not threatened by even the most violent flutter, which occurred just prior to buckling under radial external pressure loading and just after buckling under axial compressive loading. Buckled portions of a shell did not flutter. It appears that the large local curvatures encountered in the buckling of a cylindrical shell tend to stabilize the shell locally. However, it also appears that the localized buckling usually encountered in practice reduces the stability of any unbuckled regions of the shell.