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Analysis of Flow Induced by an Oscillating Fuel Bundle Open Access

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Data from an experimental campaign to understand the effects of seismic loading on a fuel bundle has been analyzed. The data considered consists of cases with initially stagnant flow. Data for the analysis has been acquired by implementing a comprehensive set of cameras, light sources and other sensors that have been operated in a synchronized manner. These acquisition tools are coupled with custom post-processing codes to obtain measurements such as structural displacement and fluid velocity fields.A proposed mechanism for the generation of flow induced by the oscillation of a bundle is presented along with characterization of the expected instabilities. Results are presented separately for pre and post instability cases.For cases prior to the generation of flow instabilities, three cases with the same nominal input conditions are analyzed to check repeatability and gain confidence in understanding the system. Structural displacement and fluid velocity measurements are presented along with displacement of the shake table. The resulting data from the different cases revealed inconsistencies, some of which are the result of changes in initial conditions of the bundle between different days of testing. Other inconsistencies indicate the importance of studying the overall bundle dynamics in a more comprehensive manner to understand the phenomenon. Such work is determined to be beyond the scope of this thesis and is reserved for the future.For cases where flow instabilities appear, a continuous wavelet transform based post-processing tool has been used to classify the nature of the induced flow into three types: no vortex shedding, repeatable vortex shedding and random vortex shedding. Representative data for the three cases along with a classification of more cases are presented. In agreement with literature, a threshold region is identified that marks the initiation of vortex shedding. This transition is believed to be important in explaining changes in damping behavior seen in real bundles.

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