The three-dimensional study of flow mixing phenomenon in a T-junction area with 90-degree bend upstream

Thermal fatigue of the structure around a T-junction is a technically important issue for the safety of nuclear power plants so for increasing capability and decreasing risk of the future power plant design. Fluid mixing characteristics in a T-junction area with a 90-degree bend upstream were studied by using Particle Image Velocimetry (PIV). The analysing of mixing phenomenon is investigated as two main bases, time series flow field and velocity fluctuation analysis. In the each part, longitudinal and lateral sections are visualized in the four different radial (r/Dm = 0.0, 0.165, 0.33, 0.41) and axial (h/Dm = 0.0, 0.25, 0.5, 1.0) positions. According to the various velocity ratio and main velocity (Vb/Vm = 0.0, 0.44, 0.66, 0.88, 1.0, 1.33, 2.0, 2.66), different branch pipe jets are existed and classified as Impinging jet, Turn jet, Wall jet and Re-attached jet. Time series data prove the appearance of vortices above branch pipe, which have same behaviour as Karman vortex. The fact shows that branch pipe jet is acting like flexible solid bar in the main pipe flow. In the case with lowest main pipe flow and highest branch pipe flow, this phenomenon is becoming clearer look like the Impinging jets. Interaction between main pipe flow and branch pipe jet produce a high intense Teardrop shape area in the mixing part, which has a high intensity of the velocity fluctuation. In the Wall jet conditions; this area is close to the main pipe wall as it touches the wall. Reattached jet divulges some different character in this area by producing a lower velocity fluctuation Bulb shape region in the centre of intense area and touch main pipe wall in the two curve line. Finally, the mixing mechanism is evaluated 3-dimensionally by various branch pipe jets. The results show us the Re-attached and Wall jets have maximum velocity fluctuation near the pipe wall and Turn jet has enormous capability to operation. (author)