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Fluid-Structure Interaction for a Cantilever Rod in Axial Flow: An Experimental Study
[Thesis]. Manchester, UK: The University of Manchester; 2018.
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Abstract
The phenomenon of fluid-structure interaction is present in many industrial applications, such as bridge cables, transmission wires, drilling risers in petroleum production, biomedical engineering, etc. In the nuclear industry, fluid-structure interactions have also been identified, one form of which is Flow-Induced Vibrations (FIVs) of the fuel rods in a typical pressurized nuclear water reactor core. As a result, the vibrating fuel rods may have contact with the neighbouring structures, such as spacer grids which are technically a structure for preventing the fuel rods from excessive movement, and concurrently initializing fretting on the fuel rod surfaces, called grid-to-rod fretting. Thus, for safety concerns, the characteristics of the flow-induced rod vibrations in such a system are required to be understood, and accordingly monitoring the wear-through failure using a prediction tool. In the present study, an experimental approach is proposed to advance our understanding of these phenomena and extend the range of available correlations. In the present experiment, a flow-induced structural vibration system has been designed, in which the geometry is prototypical of pressurized water nuclear reactor core and the flow parameters replicate the flow conditions during its full power operation. Following a validation of the methodology, a series of tests on a cantilever rod in pipe flows directed from the rod free end towards the fixed end has been carried out, in which the rod features either a blunt or a tapered free-end shape, and has been filled internally with either air or lead (for mimicking the fuel pellets in a real nuclear fuel rod). Through analysis of the resulting data, it has been found that the vibrating amplitude of a cantilever rod is more sensitive to the free-end shape of the rod, while the vibrating frequency is mostly influenced by the internal loading material. These findings give an insight into the future design of relevant structures in nuclear reactor cores, the fluid-structure interaction community will also benefit from the availability of such data to fine-tune relevant numerical codes.