<p>The study of coolant flow behavior in rod bundles is of relevance to the design of nuclear reactors. Although laminar and turbulent flows have been researched extensively, there are still gaps&nbsp;in understanding the process of laminar-turbulent&nbsp;transition. Such process may involve the formation of a gap vortex street and a related linear instability. Therefore, it is necessary to quantify under what conditions it occurs.</p><p>In the present work, a parametric study was performed to analyze the fluid instability during the laminar turbulent-transient&nbsp;flow in two square arrayed rod bundle subchannels. A three-dimensional geometric model was built in a&nbsp;finite-element mesh generator, with pitch-to-diameter ratios ranging from 1.05 to 1.25 and a length of 100 diameters. Additionally, the following premises were imposed: periodic boundary conditions at the lateral, no-slip condition at the wall, and a uniform velocity at the inlet. Then, to investigate where the transition occurred, the Reynolds number was varied from 250 to 3000. The simulations were carried out using the spectral-element code Nek5000, with a Direct Numerical Simulation (DNS) approach. Data were analyzed to examine the process of laminar-turbulent transition in this Spatio-temporal developing instability. In particular, we evaluate the location of onset and spatial growth of the instability.</p>

Study on Laminar Turbulent Transition in Square Arrayed Rod Bundles

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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