Abstract
The structure of the gas flow in cross-flow tube banks is an important factor in analyzing vibration problems including the gas column resonance, the Karman vortex excitation, and the fluid-elastic mechanism. In this paper, the structure of gas flow is investigated by means of the visualization technique and the hot wire anemometer from the viewpoint that the flow in tube banks can be treated as a complex Karman vortex flow. The results obtained by this experiment are as follows;
1. The strouhal number is strongly dependent on the size of the vortex formation region and therefore varies widely with tube spacings.
2. Several flow patterns, such as that in which the Karman vortices are not formed in tube banks, and that in which the gas flow deflects due to the Coanda effect, were identified and explained.
By using the Strouhal number obtained here, the result of a survey on the actual exhaust economizers in Diesel ships was analyzed. It was found that the present day practice is not immune from the danger of the gas column vibration.
Experiments were also carried out on the fluid-elastic vibration of tubes in a single row tube banks. It was found by this experiment that the fluid-elastic vibration has its own field of danger. The relation between the critical velocity and the tube spacing was obtained.
