Æolian tones and stall flutter of lengthy objects in fluid flows

We consider theoretically the spontaneous oscillations of an elastic cylinder in a streaming fluid flow. Such oscillations are responsible for stall flutter in e.g. turbine blades and bridges, or Æolian tones when in the acoustic range. The process of vortex separation from the oscillating surface is modelled as a self-excited oscillator. The vortex separation frequency remains synchronized with the oscillations of the cylinder over a great range of frequency mismatches, enabling the amplitudes and frequencies to be calculated. Only when the vortex separation frequency is much less than the cylinder’s natural oscillation frequency does the synchronization break down, and two-frequency oscillations (beats) then occur.