Numerical investigation on thermal striping conditions for a tee junction of LMFBR coolant pipes. 6. Numerical evaluations of arched-vortex characteristics in non-isothermal fields

Numerical analyses for turbulence thermal mixing, the aim of which is to evaluate relationship between hydrodynamics and temperature distribution of an arched-vortex, were carried out using the direct numerical simulation code DINUS-3. From the analyses, the following results have been obtained: (1) Transportation period of the arched-vortex and distance between the arched-vortices were kept constant in isothermal and non-isothermal conditions. (2) The transportation period of arched-vortex was decreased with increasing Reynolds number under the condition of the constant flow velocity ratio between both coolant pipes. (3) One of the main reasons for this behavior was considered that the motion of the cold fluid flowing out of the branch pipe was restricted by the difference of fluid density between the branch and the main pipes. The amplitudes of the cross flow velocity fluctuation in the leg region of the arched-vortex were larger than those under isothermal condition. (4) It was confirmed that the arched-vortex consists of two kinds of vortexes, i.e., a longitudinal vortex generated by a shear motion at the top of the arched-vortex, and a horizontal vortex by shedding motion at both sides of the branch jet flow. (author)