Development of analytical model for evaluating temperature fluctuation in coolant (IV); Development of analytical model for temperature fluctuation frequency using a direct numerical simulation method

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A thermal striping phenomenon characterized by a random temperature fluctuation occurs in the region immediately above the FBR core due to the temperature difference of the core outlet coolant between subassemblies. In this study, a direct numerical simulation code DINUS-3(Direct NUmerical Simulation using 3rd order upwind scheme) has been developed based on the third order upwind scheme and investigated applicability of the DINUS-3 code to temperature fluctuation analysis. From the analysis of von Karman vortex streak behind a rectangular obstacle, the following results have been obtained: (1)Change of the vortex frequency (the strouhal number St) with increase of the Reynolds number Re can be estimated by the DINUS-3 code. (2)A stationary random turbulence fluctuation including a buffer region between the transition and the turbulent regions can be predicted using the DINUS-3 code. And the followings became clear after the analysis of a nonisothermal parallel jet experiment using water. (1)A temperature fluctuation phenomenon including complicated frequency components can be simulated well using the DINUS-3 code. (2)Calculated dominant frequency has shown good agreement with the experiment. From the analysis, it is concluded that the DINUS-3 code based on the third order upwind sheme has a sufficiently high potential in providing good interpretation of experimental results related to the temperature fluctuation phenomena such as thermal striping.