Visualization of fluid mixing phenomena in T-junction with 90-degree bend upstream

For Increasing capability and decreasing risk of nuclear power plants in a future design, fluid mixing characteristics in a T-junction area with a 90-degree bend upstream were studied by using Particle Image Velocimetry (PIV). Mixing phenomenon was visualized in two longitudinal and lateral sections. In both sections, different velocity ratios with same mechanical properties were measure. In the longitudinal section of the T-junction area, the flow patterns of jet running out from the branch pipe into the main pipe could be classified Into a stratified flow type, a reattached jet flow type, a turn jet flow type and a impinging jet type, depending on velocity ratio of the branch pipe to the main pipe and main pipe velocity. Furthermore, it was visualized that there were some complicated circulating vortices around the jet, which highly affect on unsteady behavior of jet. For the visualization of lateral flow field above junction, this mixing mechanism was investigated 3-dimentionally. The detailed velocity fluctuation profiles in the case with/without the branch pipe flow were closely discussed for both flow fields. These results gave enforced hints for identifying the complex interaction between unsteady behavior of secondary flow in the decay process after the bend, the circulating vortices and the jet. Finally, unsteady behavior of flow velocity, average velocity distribution and velocity fluctuation intensity in different lateral and longitudinal conditions were compared and discussed.