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Report No.

Study on convective mixing for thermal striping phenomena; Thermal-Hydraulic analyses on mixing process in parallel triple-jet and comparisons between numerical methods

Kimura, Nobuyuki; Miyake, Yasuhiro*; not registered; Kamide, Hideki 

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing among jets imposes thermal fatigue on structural components, js of importance for reactor safety. ln the present study, a water experiment was performed on parallel triple-jet: cold jet at the center and hot jets in both sides. Three kinds of numerical analyses based on the finite difference method were carried out to compare the similarity with the experiment by use of respective different handling of turbulence such as a k-$$varepsilon$$ two equation turbulence model (k-$$varepsilon$$ Mode1), a low Reynolds number stress and heat flux equation model (LRSFM) and a direct numerical simulation (DNS). ln the experiment, the jets were mainly mixed due to the coherent oscillation. The numerical result using k-$$varepsilon$$ Model could not reproduce the coherent oscillating motion of jets due to rolling-up fluid. The oscillations of the jets predicted by LRSFM and DNS were in good agreements with the experiment. The comparison between the coherent and random components in experimental temperature fluctuation obtained by using the phase-averaging shows that k-$$varepsilon$$ Model and LRSFM overestimated the random component and the coherent component respectively. The ratios of coherent to random components in total temperature fluctuation obtained from DNS were in good agreements with the experiment. The numerical analysis using DNS can reproduce the coherent oscillation of the jets and the coherent / random components in temperature fluctuation. The analysis using LRSFM could simulate the mixing process of the jets with the low frequency.



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