Study on Mechanism for Unstable Vibrations of an Axisymmetric Body in a Cavitating Leakage Flow

Author(s):  
Masaaki Arai

An axisymmetric body in a cavitating narrow annular parallel passage attains the self-excited vibrations when the apparent passage formed by the cavitation bubbles becomes certain conditions. This paper presents experimental and analytical studies on the mechanism for such unstable vibrations. In order to examine the apparent passage, the cross-sections of the leakage flow containing the cavitation are observed in the one-dimensional leakage model. When the self-excited vibrations occur, the cavitation bubbles disappear in the vicinity of the exit. Relating these apparent passages to the annular passage, the fluid-dynamic forces acting on an axisymmetric body are investigated theoretically. The theoretical results show that the fluid-dynamic damping is negative when the unstable vibrations occur experimentally.

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1675-1678
Author(s):  
TAKAHIRO YASUDA ◽  
YASUNARI TAKANO

When a thin flat pate is released in the still air, the plate may fall aslant and automatically set into a rotational motion. This phenomenon is called autorotation. In this state, the unsteady fluid-dynamic forces act on the plate due to the vortex shedding and the rotation of the body. In this study, we focused on the auto-rotating phenomenon of an elliptic cylinder and investigated the effect of the cylinder rotation on the unsteady fluid-dynamic forces by the comparison between the result of the complex velocity potential theory and the one of numerical simulation. It was found that the low drag occurring at -160 degree phase and the high lift at zero degree phase are caused by the cylinder rotation.


2014 ◽  
Vol 92 (12) ◽  
pp. 1676-1680 ◽  
Author(s):  
Murat Yavuz ◽  
Nimet Isik ◽  
Zehra Nur Ozer ◽  
Melike Ulu ◽  
Mevlut Dogan ◽  
...  

For the first time in the literature, the angular distribution of the double-differential cross section of a methane molecule is measured and calculated at 300 and 350 eV electron impact energies. Experiments were carried out with a conventional electron spectrometer. The theoretical results were obtained using the first Born approximation and the one-Coulomb wave model corrected by the Gamow factor to take into account the post-collision interaction between the outgoing electrons. The agreement between experiment and theory indicates that the one-Coulomb wave model is a reliable theoretical approach to describe electron–methane interactions.


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