Study on convective mixing for thermal striping phenomena; Evaluation on Similarity of DNS for turbulence characteristics of mixing among jets

Kimura, Nobuyuki; Miyake, Yasuhiro*; Nagasawa, Kazuyoshi*; not registered; Kamide, Hideki ; Hishida, Koichi

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes high cycle thermal fatigue in structural components, is of importance for reactor safety. In this study, we carried out the velocity/temperature measurement using thermocouples and the particle image velocimetry in a water experiment, which had a parallel tripl-jet configuration, and a direct numerical simulation (DNS) was performed using DINUS-3 code and compared with the experimental result. As for the experimental condition, the discharged velocities of three jets were equally 0.5 m/s and the discharged temperature difference was 5C. The time-averaged temperature/velocity fields obtained from the DNS calculation were in good agreements with the experimental results including the vortex structures between the jets. The DNS calculation overestimated the turbulent quantities in the experiment. The calculated profiles of the probability density function in the velocity fluctuating components, however, were in good agreements with those in the experiment. The predicted joint probability density function between the horizontal and vertical velocity fluctuating components was close to the experimental one. It was shown that the DNS calculation well simulated the convective mixing processes between the jets from the point of view of the turbulent quantities.