Large eddy simulation of non-isothermal turbulent flow past a circular cylinder
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Copyright (2015) by American Nuclear Society All rights reserved. Understanding the thermal mixing of coolant jets in the lower plenum of High Temperature Gas-Cooled Reactors (HTGR) is very important to address certain design and safety issues. As a step towards developing an experimentally validated computational model for the lower plenum flow, turbulent flow and heat transfer around a circular cylinder is computed using large eddy simulation (LES) at three different Reynolds numbers (3000, 5900, 7400). In the range of the Reynolds number considered in this study, flow undergoes a rapid structural change with Reynolds number which significantly affects the heat transfer characteristics. The major difficulty of predicting turbulent heat transfer around a circular cylinder comes from turbulence modeling. To overcome this issue, a finite-volume solver with compressible flow formulations are used for the simulation. A sub-grid stress (SGS) model is chosen in such a way that LES can predict the physical characteristics of the flow and heat transfer. The LES results are found to be in good agreement with well-known experimental studies available in the literature. The main features of turbulent heat transfer in the subcritical regime are closely captured by LES, namely the thermal boundary layer and the sharp increase in both the mean and the r.m.s. Nusselt number in separation region. The dependence of these quantities on Reynolds number is also captured. The numerical results also confirm that the heat transfer characteristics is closely consistent with the structural change in the flow and is dependent on the Reynolds number. This research lays the groundwork needed to develop a high-fidelity experimentally validated computational model of the complex thermal mixing flow in the HTGR lower plenum.