Component failures due to excessive flow-induced vibration in reactor cores and steam generators affect the performance and reliability of nuclear power stations around the world. Numerous investigations on the axial flow within tube bundles have identified the presence of potentially damaging low frequency, large-scale co- herent patterns. This Thesis reports a first detailed investigation into the effect of a streamwise separation between each pair of consecutive rod bundles on the flow structure. Turbulent flow in an annular channel with a sudden expansion between the inner cylinders is studied numerically. The calculations are performed using wall-resolved Large Eddy Simulation (LES) for which the generation of turbulent inlet conditions is achieved through the development and evaluation of the precur- sor and recycling inlet methods in the framework of Code Saturne. Results are presented for a fully concentric configuration in which three streamwise separation lengths based on the inner rod diameter, Drod, are considered, namely 2 × Drod (‘2Dc' case), 4×Drod (‘4Dc' case) and 6×Drod (‘6Dc' case). It is shown that the flow structure in the inter-rod spacing is highly dependent on the length of the streamwise gap. The characteristic flow features discerned in the narrow ‘2Dc' case suggest a striking similarity with flow over d-type rib-roughness, whereas the larger gap lengths in the ‘4Dc' and ‘6Dc' configurations lead to flow patterns comparable to those in k-type roughness. The effect of downstream eccentricity is examined for configurations with a streamwise gap length of 2 × Drod (‘2De' case) and 6 × Drod (‘6De' case). The results reveal that the misalignment of the downstream rod with respect to the upstream cylinder has a significant impact on the flow behaviour in the narrow ‘2De' case, whilst the ‘6De' case presents reasonable agreement with its concentric counterpart.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:629400 |
| Date | January 2014 |
| Creators | Newlands, Kristin |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=214845 |
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