Vibration and aeroelastic stability of a disk rotating in a fluid.

摘要

This dissertation investigates the vibration of a supercritical speed disk spinning in a fluid. It first shows that friction-generated radial traction at the clamping collar affects strongly the disk natural frequencies. The discrepancy between idealized theories and experiment grows with speed, exceeding 13% at high supercritical speed. Subsequent start/stop cycles of rotation show hysteresis of the natural frequencies. Friction, stiction, and slippage of the disk between the collars cause the discrepancies between experiment and idealized theories, which do not model friction. By superposing the stress field by an empirically determined friction radial traction with centrifugal stresses predicted by an idealized model, predicted frequencies agree with experiment at all speeds for most modes.;A linear aeroelastic stability analysis shows that the disk experiences traveling wave flutter. It models the system as a classical plate spinning in an inviscid, compressible fluid. A finite Hankel transform technique determines the fluid motion as a function of the vibration, and the spectral Galerkin method reduces the continuous system to a discrete system. Incompressible flow is then assumed. The analysis predicts the flutter mode. Prediction of flutter frequency as a function of flutter speed agrees qualitatively with experiment.;Experiments then describe the aerodynamically excited supercritical disk vibration. For most fluid densities, a single supercritical backward wave becomes unstable. At pre-flutter speeds, the disk vibrates at its natural frequencies because of excitation from unsteady fluid pressure, but at the flutter speed and at higher speeds the fluid and the disk are strongly coupled. Coupling can be so strong that the post-flutter frequency becomes nearly independent of rotation speed, even though the disk stiffens with increasing speed. Frequency and amplitude measurements when the fluid is at sub-atmospheric pressure show how the flutter speed, frequency, and mode depend on the ratio of the fluid density to the disk density. They also show that disk flutter occurs in subsonic and often in incompressible flow.