Nonlinear aeroelastic flutter phenomena of a flexible disk rotating in an unbounded fluid

Aeroelastic flutter in rotating disks is of interest in a number of applications including data storage systems, circular saws and microturbines. This paper presents new experimental results on the nonlinear aeroelastic flutter phenomena of a flexible disk rotating in an unbounded fluid. The experiments are performed on thin steel and paper disks over a wide range of rotation speeds in the post-flutter region with very fine, computer-controlled increments of the rotation speed. The existence of a primary instability of a reflected travelling wave of the disk, followed by a secondary instability, is confirmed. However, at speeds exceeding that at which the secondary bifurcation occurs, complicated, hitherto unrecorded nonlinear response is observed, including several solution branches and bifurcation points, frequency lock-ins over certain rotation speed ranges, presence of higher harmonics of the unstable wave and large frequency and amplitude hysterisis, as the disk speed is ramped up and down across these bifurcations. It is shown that a nonlinear von Kármán plate model for the disk, coupled with a linear aerodynamic load having the form of a rotating damping pressure, is capable of capturing the primary instability branch. However, such a model is inadequate in capturing the secondary bifurcation and the complicated nonlinear response that follows.