Flow-Induced Vibration of a Circular Cylindrical Shell. 1st Report. Experiments on the Stability under Leakage Flow through Internal Annular Gap.

Abstract

The unstable region of a circular cylindrical aluminium shell subjected to internal leakage flow was investigated experimentally, changing the gap shape and leakage flow velocity. The changes in the natural frequency, damping ratio, and displacement were also investigated to clarify the type of instability that occurred and to obtain the vibration characteristics needed for predicting instability. Flutter-type instability was observed and for an unstable gap condition, the damping ratio decreased to zero, as is known to occur with flutter-type instability. Moreover, the natural frequency increased with the flow velocity. The change in the natural frequency was small and the damping ratio increased with the leakage flow velocity when the gap shape was stable. The repeability of the flutter occurrence was good. Leakage flow through a straight gap did not cause instability, and the critical ratio of the size of the stepped annular gap for the unstable region was obtained.