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Thermal striping caused by the mixing of fluids at different temperatures is one of the most important issues in the design of Sodium cooled Fast Reactors (SFRs), because it may cause high-cycle thermal fatigue in the structure and affect the structural integrity. A numerical simulation code named MUGTHES has been developed to investigate thermal striping phenomena and to estimate high-cycle thermal fatigue in SFRs. In this study, the numerical simulation of the WATLON which was a water experiment of the T-junction piping system conducted by the Japan Atomic Energy Agency (JAEA) was conducted to validate the MUGTHES as a typical problem of thermal striping and to investigate the temperature fluctuation generation mechanism relating to the unsteady motion of large eddy structures. In the numerical simulation, an approach using the large eddy simulation (LES) with the standard Smagorinsky model was employed to simulate large scale eddy motions in the T-pipe. To quantify the uncertainty of the numerical results, the Grid Convergence Index (GCI) estimation was examined using two modified methods from the Roache’s GCI method described in the ASME V&V-20 guideline and the Eça-Hoekstra’s least square version GCI. The modified least square version GCI was named SLS-GCI (Simplified Least Square version GCI estimation method). Three mesh arrangements were employed to estimate the GCI value for uncertainty quantification in the validation process. Through the GCI estimation, it was found that the SLS-GCI method could successfully quantify the uncertainty of the numerical results. The numerical results suggested that the fine mesh arrangement in this study could improve the temperature distribution in the wake and that the thermal mixing phenomena in the T-pipe were caused by the mutual interaction of the necklace-shaped vortex around the wake from the front of the branch jet, the horseshoe-shaped vortex, and Karman’s vortex motions in the wake.

mechanical engineering journal

Numerical simulation of thermal striping phenomena in a T-junction piping system for fundamental validation and uncertainty quantification by GCI estimation