Numerical investigation on local heat transfer under large scale eddy motion

Temperature fluctuation caused by the turbulence mixing of different temperature fluids gives thermal fatigue to structure according its amplitude and frequency. This phenomenon is significant as safety issue in liquid metal cooled fast reactor (LMFBR). In Japan Nuclear Cycle Development Institute (JNC), experimental and numerical investigations have been carried out to clarify the turbulence mixing phenomena and to establish an evaluation rule for the thermal fatigue in LMFBR. Large-scale eddy motion in turbulence mixing causes the temperature fluctuation with large amplitude and low frequency component. In the estimation of thermal fatigue, heat transfer coefficient under large-scale eddy motion and such a temperature fluctuation are important factors for accurate prediction of thermal stress in the structure. In this study, numerical simulation was carried out to investigate the local heat transfer mechanism under large-scale eddy motion and the treatment of heat transfer coefficient in the transient phenomena was discussed in relation to the thermal fatigue estimation. (authors)