Torsional flutter of bluff bodies

This paper describes the torsional flutter mechanism of 2D rectangular cylinders and 2D H-shaped cylinders based upon unsteady pressure measurements under forced torsional vibration. For some cylinders with certain side ratio (BD, B: chord length, D: cylinder thickness), such as BD = 5 to BD = 12.5, in the high reduced velocity range, that is V/f B> 10 (f: torsional frequency, V: approaching flow velocity), the torsional flutter mechanism is fundamentally identical with that of coupled flutter, however, in the low reduced velocity range, that is roughly V/f B # 8, the torsional flutter would be induced by vortex convection along side-surface of the cylinder, which is evidently different from that of coupled flutter. Furthermore, for bluffer cylinders such as 2D rectangular cylinders with BD = 2 and 2D H-shaped cylinder with BD = 3, torsional flutter shows a particular characteristic of velocity-restricted type, but not divergent type in smooth flow. This flutter is mainly controlled by the phase difference between separated flow from the leading edge and torsional response, which gradually changes with flow velocity, where vortex convection seems to play a less important role in the excitation.