| Parallel plate-type fuel assemblies were used in some advanced research reactors and military reactors because of its high power density and good heat transportation characteristics. Coolant flow through narrow rectangular channel, which between two adjacent fuel plates, may induce severe fluid-structure interaction (FSI) between the flowing fluid and the vibrating plates. Such FSI phenomena could threaten the operation safety of nuclear reactors. For any fuel plate of parallel flat plate-type fuel assemblies could be considered as a flexible plate in a rectangular channel. Therefore, it is of great importance to perform deep research on FIV mechanism of flat plate in a rigid rectangular channel. Characteristics of the large amplitude and narrow-band vibration of a flexible flat plate, which is foursquare-supported in a rigid rectangular channel, were investigated by numerical and experimental methods. In the simulation, vortex shedding characteristics of a rigid flat plate, which was double-edges fixed and exposed to an axial flow within a rigid rectangular channel, was calculated by changing the width of the channel, and the around flow problems were classified into three classifications which with broad channel, mild channel and narrow channel according to the results of the simulation investigation. In terms of the characteristics of the three types issues, the designing of the FSI experiments was initially set to be a around flow issue with broad channel, therefore, structure dimensions of the test plate and test section were confirmed. In the FIV experiments, self-designed test section and test plate were used, the flexible test plate was foursquare-supported within the rectangular test section and exposed to an axial water flow, and the laser sensor technology was used to measure the vibration displacement. The narrow-band vibration phenomenon with large amplitude was observed firstly in home and abroad by changing the flow rate of the fluid within the test section. And also, narrow-band vibration with large amplitude experiments were performed in case of flexible flat plate had different thicknesses, while the natural vibration characteristics of the test plates in air were measured and the natural vibration frequencies of the test plates in static water were calculated according to added mass theory of column. As a result, it was concluded that the flowing fluid and the vibrating plate resonated and induced the large-amplitude and narrow-band vibration phenomenon. Further more, the occurring condition and some important narrow-band vibrations characteristics of a foursquare-supported flexible flat plat were investigated, which afford theoretic basis for FSI mechanism research of parallel-plate type assemblies in future. The narrow-band vibration phenomenon with large amplitude is a new FSI mechanism which can lead to the plate-type assemblies' fatigue and damage. And the new find will provide a powerful theory regulation and could be a new guide of the nuclear engineering designing for avoiding fluid-structure interaction problems of plate-type fuel assemblies. |
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