Leakage-Flow-Induced Vibrations of an Axisymmetric Body : 4th Report, Theories and Experiments on the Stability of an Axisymmetric Body for One Degree of Freedom of Rotational Motion

We present analytical and experimental studies on the stability of an axisymmetric body which vibrates with one degree of freedom of rotational motion. The leakage types are tested for three divergent passages and one parallel passage. When the flow rate of water is gradually increased or decreased, the damping ratio of the system and Reynolds number at the stability boundary are measured. It is determined that the most influential parameter on the stability of the system is the position of the pivot. When the pivot is situated downstream of the outlet, dynamic instabilities due to negative damping occur in the case of the divergent passages and static instabilities due to negative stiffness occur in the case of the parallel passage. If the pivot is situated upstream of the inlet, the systems become stable for all passages. The Reynolds number at the stability boundary increases linearly with increasing natural frequency. Since the calculated results agree well with the experimental results, we conclude that the theory on the stability of the system is reasonable.